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Author name code: christensen-dalsgaard
ADS astronomy entries on 2022-09-14
author:"Christensen-Dalsgaard, Jorgen"
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Title: Evolution of dipolar mixed-mode coupling factor in red giant
stars: impact of buoyancy spike
Authors: Jiang, C.; Cunha, M.; Christensen-Dalsgaard, J.; Zhang,
Q. S.; Gizon, L.
2022MNRAS.515.3853J Altcode: 2022arXiv220709878J; 2022MNRAS.tmp.1954J
Mixed modes observed in red giants allow for investigation of the
stellar interior structures. One important feature in these structures
is the buoyancy spike caused by the discontinuity of the chemical
gradient left behind during the first dredge-up. The buoyancy spike
emerges at the base of the convective zone in low-luminosity red
giants and later becomes a glitch when the g-mode cavity expands
to encompass the spike. Here, we study the impact of the buoyancy
spike on the dipolar mixed modes using stellar models with different
properties. We find that the applicability of the asymptotic formalisms
for the coupling factor, q, varies depending on the location of the
evanescent zone, relative to the position of the spike. Significant
deviations between the value of q inferred from fitting the oscillation
frequencies and either of the formalisms proposed in the literature are
found in models with a large frequency separation in the interval 5-15
μHz, with evanescent zones located in a transition region that may be
thin or thick. However, it is still possible to reconcile q with the
predictions from the asymptotic formalisms, by choosing which formalism
to use according to the value of q. For stars approaching the luminosity
bump, the buoyancy spike becomes a glitch and strongly affects the mode
frequencies. Fitting the frequencies without accounting for the glitch
leads to unphysical variations in the inferred q, but we show that this
is corrected when properly accounting for the glitch in the fitting.
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Title: Towards solar measurements of nuclear reaction rates
Authors: Bellinger, Earl Patrick; Christensen-Dalsgaard, Jørgen
2022arXiv220613570B Altcode:
Nuclear reaction rates are a fundamental yet uncertain ingredient in
stellar evolution models. The astrophysical S-factor pertaining to
the initial reaction in the proton-proton chain is uncertain at the
1% level, which contributes a systematic but generally unpropagated
error of similar order in the theoretical ages of stars. In this work,
we study the prospect of improving the measurement of this and other
reaction rates in the pp chain and CNO cycle using helioseismology
and solar neutrinos. We show that when other aspects of the solar
model are improved, then it shall be possible using current solar
data to improve the precision of this measurement by nearly an order
of magnitude, and hence the corresponding uncertainty on the ages of
low-mass stars by a similar amount.
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Title: Core overshoot constrained by the absence of a solar convective
core and some solar-like stars
Authors: Zhang, Qian-Sheng; Christensen-Dalsgaard, Jørgen; Li, Yan
2022MNRAS.512.4852Z Altcode: 2022arXiv220308686Z; 2022MNRAS.tmp..742Z
Convective-core overshoot mixing is a significant uncertainty in stellar
evolution. Because numerical simulations and turbulent convection
models predict exponentially decreasing radial rms turbulent velocity,
a popular treatment for overshoot mixing is to apply a diffusion
process with an exponentially decreasing diffusion coefficient. It is
important to investigate the parameters of the diffusion coefficient
because they determine the efficiency of the mixing in the overshoot
region. In this paper, we have investigated the effects of the core
overshoot mixing on the properties of the core in solar models. We have
constrained the parameters of the overshoot model by using helioseismic
inferences and the observation of the solar <SUP>8</SUP>B neutrino
flux. For solar-mass stars, the core overshoot mixing helps to prolong
the lifetime of the convective core developed at the zero-age main
sequence. If the strength of the mixing is sufficiently high, then the
convective core in a solar model could survive until the present solar
age, leading to large deviations of the sound speed and density profiles
compared with the helioseismic inferences. The <SUP>8</SUP>B neutrino
flux also favours a radiative solar core. These observations provide
a constraint on the parameters of the exponential diffusion model of
the convective overshoot mixing. A limited asteroseismic investigation
of 13 Kepler low-mass stars with 1.0 < M/M<SUB>⊙</SUB> < 1.5
shows a mass-dependent range of the overshoot parameter. The overshoot
mixing processes for different elements are analysed in detail. It is
found that the exponential diffusion overshoot model leads to different
effective overshoot mixing lengths for elements with different nuclear
equilibrium time-scales.
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Title: ET White Paper: To Find the First Earth 2.0
Authors: Ge, Jian; Zhang, Hui; Zang, Weicheng; Deng, Hongping; Mao,
Shude; Xie, Ji-Wei; Liu, Hui-Gen; Zhou, Ji-Lin; Willis, Kevin; Huang,
Chelsea; Howell, Steve B.; Feng, Fabo; Zhu, Jiapeng; Yao, Xinyu; Liu,
Beibei; Aizawa, Masataka; Zhu, Wei; Li, Ya-Ping; Ma, Bo; Ye, Quanzhi;
Yu, Jie; Xiang, Maosheng; Yu, Cong; Liu, Shangfei; Yang, Ming; Wang,
Mu-Tian; Shi, Xian; Fang, Tong; Zong, Weikai; Liu, Jinzhong; Zhang, Yu;
Zhang, Liyun; El-Badry, Kareem; Shen, Rongfeng; Tam, Pak-Hin Thomas;
Hu, Zhecheng; Yang, Yanlv; Zou, Yuan-Chuan; Wu, Jia-Li; Lei, Wei-Hua;
Wei, Jun-Jie; Wu, Xue-Feng; Sun, Tian-Rui; Wang, Fa-Yin; Zhang,
Bin-Bin; Xu, Dong; Yang, Yuan-Pei; Li, Wen-Xiong; Xiang, Dan-Feng;
Wang, Xiaofeng; Wang, Tinggui; Zhang, Bing; Jia, Peng; Yuan, Haibo;
Zhang, Jinghua; Xuesong Wang, Sharon; Gan, Tianjun; Wang, Wei; Zhao,
Yinan; Liu, Yujuan; Wei, Chuanxin; Kang, Yanwu; Yang, Baoyu; Qi, Chao;
Liu, Xiaohua; Zhang, Quan; Zhu, Yuji; Zhou, Dan; Zhang, Congcong;
Yu, Yong; Zhang, Yongshuai; Li, Yan; Tang, Zhenghong; Wang, Chaoyan;
Wang, Fengtao; Li, Wei; Cheng, Pengfei; Shen, Chao; Li, Baopeng; Pan,
Yue; Yang, Sen; Gao, Wei; Song, Zongxi; Wang, Jian; Zhang, Hongfei;
Chen, Cheng; Wang, Hui; Zhang, Jun; Wang, Zhiyue; Zeng, Feng; Zheng,
Zhenhao; Zhu, Jie; Guo, Yingfan; Zhang, Yihao; Li, Yudong; Wen, Lin;
Feng, Jie; Chen, Wen; Chen, Kun; Han, Xingbo; Yang, Yingquan; Wang,
Haoyu; Duan, Xuliang; Huang, Jiangjiang; Liang, Hong; Bi, Shaolan; Gai,
Ning; Ge, Zhishuai; Guo, Zhao; Huang, Yang; Li, Gang; Li, Haining;
Li, Tanda; Yuxi; Lu; Rix, Hans-Walter; Shi, Jianrong; Song, Fen;
Tang, Yanke; Ting, Yuan-Sen; Wu, Tao; Wu, Yaqian; Yang, Taozhi; Yin,
Qing-Zhu; Gould, Andrew; Lee, Chung-Uk; Dong, Subo; Yee, Jennifer C.;
Shvartzvald, Yossi; Yang, Hongjing; Kuang, Renkun; Zhang, Jiyuan;
Liao, Shilong; Qi, Zhaoxiang; Yang, Jun; Zhang, Ruisheng; Jiang, Chen;
Ou, Jian-Wen; Li, Yaguang; Beck, Paul; Bedding, Timothy R.; Campante,
Tiago L.; Chaplin, William J.; Christensen-Dalsgaard, Jørgen; García,
Rafael A.; Gaulme, Patrick; Gizon, Laurent; Hekker, Saskia; Huber,
Daniel; Khanna, Shourya; Li, Yan; Mathur, Savita; Miglio, Andrea;
Mosser, Benoît; Ong, J. M. Joel; Santos, Ângela R. G.; Stello,
Dennis; Bowman, Dominic M.; Lares-Martiz, Mariel; Murphy, Simon; Niu,
Jia-Shu; Ma, Xiao-Yu; Molnár, László; Fu, Jian-Ning; De Cat, Peter;
Su, Jie; consortium, the ET
2022arXiv220606693G Altcode:
We propose to develop a wide-field and ultra-high-precision photometric
survey mission, temporarily named "Earth 2.0 (ET)". This mission is
designed to measure, for the first time, the occurrence rate and the
orbital distributions of Earth-sized planets. ET consists of seven
30cm telescopes, to be launched to the Earth-Sun's L2 point. Six
of these are transit telescopes with a field of view of 500 square
degrees. Staring in the direction that encompasses the original Kepler
field for four continuous years, this monitoring will return tens of
thousands of transiting planets, including the elusive Earth twins
orbiting solar-type stars. The seventh telescope is a 30cm microlensing
telescope that will monitor an area of 4 square degrees toward the
galactic bulge. This, combined with simultaneous ground-based KMTNet
observations, will measure masses for hundreds of long-period and
free-floating planets. Together, the transit and the microlensing
telescopes will revolutionize our understandings of terrestrial
planets across a large swath of orbital distances and free space. In
addition, the survey data will also facilitate studies in the fields
of asteroseismology, Galactic archeology, time-domain sciences, and
black holes in binaries.
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Title: Searching for dark energy with the Sun
Authors: Saltas, Ippocratis D.; Christensen-Dalsgaard, Jørgen
2022arXiv220514134S Altcode:
General extensions of General Relativity (GR) based on bona fide
degrees of freedom predict a fifth force which operates within massive
objects, opening up an exciting opportunity to perform precision tests
of gravity at stellar scales. Here, focusing on general scalar-tensor
theories for dark energy, we utilize the Sun as our laboratory and
search for imprints of the fifth-force effect on the solar equilibrium
structure. With analytic results and numerical simulations, we
explain how the different solar regions offer powerful ways to test
gravity. Accounting for the delicate interplay between fifth force
and solar microphysics such as opacity, diffusion, equation of state
and metallicity, we demonstrate that the fifth force still leaves
a sharp signature on the solar sound speed, in a region where simple
estimates of input physics uncertainties become negligible. For general
scalar-field extensions of GR, known as (U-)DHOST, based solely on the
observational helioseismic errors, our analysis at the equilibrium level
allows to place an approximate constraint on the fifth-force coupling
strength of $-10^{-3} \lesssim \mathcal{Y} \lesssim 5\cdot 10^{-4}$
at $2\sigma$. This result improves previous stellar constraints by
$\sim 3$ orders of magnitude, and should be confirmed and improved
by future helioseismic inversions in modified gravity combined with
an elaborate accounting of theoretical uncertainties. Our analysis
can be applied to a wide set of theories beyond GR, and also paves
the way for helioseismic analyses in this context. In this regard,
we discuss how the solar radiative and convective zone can be employed
as promising laboratories to test generic theories of gravity.
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Title: VizieR Online Data Catalog: LCs of RR Lyrae stars from TESS
(Molnar+, 2022)
Authors: Molnar, L.; Bodi, A.; Pal, A.; Bhardwaj, A.; Hambsch,
F. -J.; Benko, J. M.; Derekas, A.; Ebadi, M.; Joyce, M.; Hasanzadeh,
A.; Kolenberg, K.; Lund, M. B.; Nemec, J. M.; Netzel, H.; Ngeow,
C. -C.; Pepper, J.; Plachy, E.; Prudil, Z.; Siverd, R. J.; Skarka,
M.; Smolec, R.; Sodor, A.; Sylla, S.; Szabo, P.; Szabo, R.; Kjeldsen,
H.; Christensen-Dalsgaard, J.; Ricker, G. R.
2022yCat..22580008M Altcode:
In this paper we studied an initial selection of 126 known or candidate
bright RR Lyrae stars within Sectors 1 and 2 of the Transiting
Exoplanet Survey Satellite (TESS) mission, 118 of which turned out to
be real pulsators. <P />Sectors 1 and 2 lasted for 27.9 and 27.4 days,
with 1.13 and 1.44day long mid-sector gaps, respectively. During each
sector, the entire field of view is recorded as full-frame images (FFI)
at a 30 minute cadence, while selected targets are measured with 2
minute cadence. <P />In Sectors 1 and 2, three targets were observed
as 2 minute cadence targets, part of the TESS Asteroseismic Science
Consortium (TASC) target list (ST Pic in both sectors, BV Aqr in S1,
and RU Scl in S2). The rest of the RR Lyrae stars were FFI targets. See
Section 2. <P />(11 data files).
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Title: No swan song for Sun-as-a-star helioseismology: Performances
of the Solar-SONG prototype for individual mode characterisation
Authors: Breton, S. N.; Pallé, P. L.; García, R. A.; Fredslund
Andersen, M.; Grundahl, F.; Christensen-Dalsgaard, J.; Kjeldsen, H.;
Mathur, S.
2022A&A...658A..27B Altcode: 2021arXiv211012698B
The GOLF instrument on board SoHO has been in operation for almost 25
years, but the ageing of the instrument has now strongly affected its
performance, especially in the low-frequency pressure-mode (p-mode)
region. At the end of the SoHO mission, the ground-based network
BiSON will remain the only facility able to perform Sun-integrated
helioseismic observations. Therefore, we want to assess the helioseismic
performances of an échelle spectrograph such as SONG. The high
precision of such an instrument and the quality of the data acquired
for asteroseismic purposes call for an evaluation of the instrument's
ability to perform global radial-velocity measurements of the solar
disk. Data acquired during the Solar-SONG 2018 observation campaign
at the Teide Observatory are used to study mid- and low-frequency
p modes. A Solar-SONG time series of 30 days in duration is reduced
with a combination of the traditional IDL iSONG pipeline and a new
Python pipeline described in this paper. A mode fitting method built
around a Bayesian approach is then performed on the Solar-SONG and
contemporaneous GOLF, BiSON, and HMI data. For this contemporaneous time
series, Solar-SONG is able to characterise p modes at a lower frequency
than BiSON or GOLF (1750 μHz versus 1946 and 2157 μHz, respectively),
while for HMI it is possible to characterise a mode at 1686 μHz. The
decrease in GOLF sensitivity is then evaluated through the evolution
of its low-frequency p-mode characterisation abilities over the years:
a set of 30-day-long GOLF time series, considered at the same period
of the year from 1996 to 2017, is analysed. We show that it is more
difficult to accurately characterise p modes in the range 1680 to 2160
μHz when considering the most recent time series. By comparing the
global power level of different frequency regions, we also observe that
the Solar-SONG noise level in the 1000 to 1500 μHz region is lower
than for any GOLF subseries considered in this work. While the global
p-mode power-level ratio is larger for GOLF during the first years
of the mission, this ratio decreases over the years and is bested by
Solar-SONG for every time series after 2000. All these observations
strongly suggest that efforts should be made towards deploying more
Solar-SONG nodes in order to acquire longer time series with better
duty cycles.
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Title: A 20 Second Cadence View of Solar-type Stars and Their Planets
with TESS: Asteroseismology of Solar Analogs and a Recharacterization
of π Men c
Authors: Huber, Daniel; White, Timothy R.; Metcalfe, Travis S.;
Chontos, Ashley; Fausnaugh, Michael M.; Ho, Cynthia S. K.; Van Eylen,
Vincent; Ball, Warrick H.; Basu, Sarbani; Bedding, Timothy R.; Benomar,
Othman; Bossini, Diego; Breton, Sylvain; Buzasi, Derek L.; Campante,
Tiago L.; Chaplin, William J.; Christensen-Dalsgaard, Jørgen; Cunha,
Margarida S.; Deal, Morgan; García, Rafael A.; García Muñoz,
Antonio; Gehan, Charlotte; González-Cuesta, Lucía; Jiang, Chen;
Kayhan, Cenk; Kjeldsen, Hans; Lundkvist, Mia S.; Mathis, Stéphane;
Mathur, Savita; Monteiro, Mário J. P. F. G.; Nsamba, Benard; Ong,
Jia Mian Joel; Pakštienė, Erika; Serenelli, Aldo M.; Silva Aguirre,
Victor; Stassun, Keivan G.; Stello, Dennis; Norgaard Stilling,
Sissel; Lykke Winther, Mark; Wu, Tao; Barclay, Thomas; Daylan, Tansu;
Günther, Maximilian N.; Hermes, J. J.; Jenkins, Jon M.; Latham,
David W.; Levine, Alan M.; Ricker, George R.; Seager, Sara; Shporer,
Avi; Twicken, Joseph D.; Vanderspek, Roland K.; Winn, Joshua N.
2022AJ....163...79H Altcode: 2021arXiv210809109H
We present an analysis of the first 20 second cadence light curves
obtained by the TESS space telescope during its extended mission. We
find improved precision of 20 second data compared to 2 minute data for
bright stars when binned to the same cadence (≍10%-25% better for T
≲ 8 mag, reaching equal precision at T ≍ 13 mag), consistent with
pre-flight expectations based on differences in cosmic-ray mitigation
algorithms. We present two results enabled by this improvement. First,
we use 20 second data to detect oscillations in three solar analogs
(γ Pav, ζ Tuc, and π Men) and use asteroseismology to measure their
radii, masses, densities, and ages to ≍1%, ≍3%, ≍1%, and ≍20%
respectively, including systematic errors. Combining our asteroseismic
ages with chromospheric activity measurements, we find evidence that the
spread in the activity-age relation is linked to stellar mass and thus
the depth of the convection zone. Second, we combine 20 second data and
published radial velocities to recharacterize π Men c, which is now the
closest transiting exoplanet for which detailed asteroseismology of the
host star is possible. We show that π Men c is located at the upper
edge of the planet radius valley for its orbital period, confirming
that it has likely retained a volatile atmosphere and that the
"asteroseismic radius valley" remains devoid of planets. Our analysis
favors a low eccentricity for π Men c (<0.1 at 68% confidence),
suggesting efficient tidal dissipation (Q/k <SUB>2,1</SUB> ≲ 2400)
if it formed via high-eccentricity migration. Combined, these early
results demonstrate the strong potential of TESS 20 second cadence
data for stellar astrophysics and exoplanet science.
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Title: First Results on RR Lyrae Stars with the TESS Space Telescope:
Untangling the Connections between Mode Content, Colors, and Distances
Authors: Molnár, L.; Bódi, A.; Pál, A.; Bhardwaj, A.; Hambsch,
F. -J.; Benkő, J. M.; Derekas, A.; Ebadi, M.; Joyce, M.; Hasanzadeh,
A.; Kolenberg, K.; Lund, M. B.; Nemec, J. M.; Netzel, H.; Ngeow,
C. -C.; Pepper, J.; Plachy, E.; Prudil, Z.; Siverd, R. J.; Skarka, M.;
Smolec, R.; Sódor, Á.; Sylla, S.; Szabó, P.; Szabó, R.; Kjeldsen,
H.; Christensen-Dalsgaard, J.; Ricker, G. R.
2022ApJS..258....8M Altcode: 2021arXiv210907329M
The Transiting Exoplanet Survey Satellite (TESS) space telescope is
collecting continuous, high-precision optical photometry of stars
throughout the sky, including thousands of RR Lyrae stars. In this
paper, we present results for an initial sample of 118 nearby RR Lyrae
stars observed in TESS Sectors 1 and 2. We use differential image
photometry to generate light curves and analyze their mode content
and modulation properties. We combine accurate light-curve parameters
from TESS with parallax and color information from the Gaia mission
to create a comprehensive classification scheme. We build a clean
sample, preserving RR Lyrae stars with unusual light-curve shapes,
while separating other types of pulsating stars. We find that a large
fraction of RR Lyrae stars exhibit various low-amplitude modes, but
the distribution of those modes is markedly different from those of the
bulge stars. This suggests that differences in physical parameters have
an observable effect on the excitation of extra modes, potentially
offering a way to uncover the origins of these signals. However,
mode identification is hindered by uncertainties when identifying
the true pulsation frequencies of the extra modes. We compare mode
amplitude ratios in classical double-mode stars to stars with extra
modes at low amplitudes and find that they separate into two distinct
groups. Finally, we find a high percentage of modulated stars among the
fundamental mode pulsators, but also find that at least 28% of them
do not exhibit modulation, confirming that a significant fraction of
stars lack the Blazhko effect.
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Title: The BAyesian STellar algorithm (BASTA): a fitting tool
for stellar studies, asteroseismology, exoplanets, and Galactic
archaeology
Authors: Aguirre Børsen-Koch, V.; Rørsted, J. L.; Justesen, A. B.;
Stokholm, A.; Verma, K.; Winther, M. L.; Knudstrup, E.; Nielsen,
K. B.; Sahlholdt, C.; Larsen, J. R.; Cassisi, S.; Serenelli, A. M.;
Casagrande, L.; Christensen-Dalsgaard, J.; Davies, G. R.; Ferguson,
J. W.; Lund, M. N.; Weiss, A.; White, T. R.
2022MNRAS.509.4344A Altcode: 2021arXiv210914622A; 2021MNRAS.tmp.2660B
We introduce the public version of the BAyesian STellar Algorithm
(BASTA), an open-source code written in PYTHON to determine stellar
properties based on a set of astrophysical observables. BASTA has
been specifically designed to robustly combine large data sets that
include asteroseismology, spectroscopy, photometry, and astrometry. We
describe the large number of asteroseismic observations that can be fit
by the code and how these can be combined with atmospheric properties
(as well as parallaxes and apparent magnitudes), making it the most
complete analysis pipeline available for oscillating main-sequence,
subgiant, and red giant stars. BASTA relies on a set of pre-built
stellar isochrones or a custom-designed library of stellar tracks, which
can be further refined using our interpolation method (both along and
across stellar tracks or isochrones). We perform recovery tests with
simulated data that reveal levels of accuracy at the few percent level
for radii, masses, and ages when individual oscillation frequencies
are considered, and show that asteroseismic ages with statistical
uncertainties below 10 per cent are within reach if our stellar models
are reliable representations of stars. BASTAis extensively documented
and includes a suite of examples to support easy adoption and further
development by new users.
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Title: Solar structure and evolution
Authors: Christensen-Dalsgaard, Jørgen
2021LRSP...18....2C Altcode: 2020arXiv200706488C
The Sun provides a critical benchmark for the general study of stellar
structure and evolution. Also, knowledge about the internal properties
of the Sun is important for the understanding of solar atmospheric
phenomena, including the solar magnetic cycle. Here I provide a brief
overview of the theory of stellar structure and evolution, including the
physical processes and parameters that are involved. This is followed
by a discussion of solar evolution, extending from the birth to the
latest stages. As a background for the interpretation of observations
related to the solar interior I provide a rather extensive analysis of
the sensitivity of solar models to the assumptions underlying their
calculation. I then discuss the detailed information about the solar
interior that has become available through helioseismic investigations
and the detection of solar neutrinos, with further constraints provided
by the observed abundances of the lightest elements. Revisions in the
determination of the solar surface abundances have led to increased
discrepancies, discussed in some detail, between the observational
inferences and solar models. I finally briefly address the relation
of the Sun to other similar stars and the prospects for asteroseismic
investigations of stellar structure and evolution.
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Title: PLATO hare-and-hounds exercise: asteroseismic model fitting
of main-sequence solar-like pulsators
Authors: Cunha, M. S.; Roxburgh, I. W.; Aguirre Børsen-Koch, V.;
Ball, W. H.; Basu, S.; Chaplin, W. J.; Goupil, M. -J.; Nsamba,
B.; Ong, J.; Reese, D. R.; Verma, K.; Belkacem, K.; Campante, T.;
Christensen-Dalsgaard, J.; Clara, M. T.; Deheuvels, S.; Monteiro,
M. J. P. F. G.; Noll, A.; Ouazzani, R. M.; Rørsted, J. L.; Stokholm,
A.; Winther, M. L.
2021MNRAS.508.5864C Altcode: 2021MNRAS.tmp.2643C; 2021arXiv211003332C
Asteroseismology is a powerful tool to infer fundamental stellar
properties. The use of these asteroseismic-inferred properties in a
growing number of astrophysical contexts makes it vital to understand
their accuracy. Consequently, we performed a hare-and-hounds exercise
where the hares simulated data for six artificial main-sequence stars
and the hounds inferred their properties based on different inference
procedures. To mimic a pipeline such as that planned for the PLATO
mission, all hounds used the same model grid. Some stars were simulated
using the physics adopted in the grid, others a different one. The
maximum relative differences found (in absolute value) between the
inferred and true values of the mass, radius, and age were 4.32, 1.33,
and 11.25 per cent, respectively. The largest systematic differences in
radius and age were found for a star simulated assuming gravitational
settling, not accounted for in the model grid, with biases of -0.88
per cent (radius) and 8.66 per cent (age). For the mass, the most
significant bias (-3.16 per cent) was found for a star with a helium
enrichment ratio outside the grid range. Moreover, an ~7 per cent
dispersion in age was found when adopting different prescriptions
for the surface corrections or shifting the classical observations
by ±1σ. The choice of the relative weight given to the classical
and seismic constraints also impacted significantly the accuracy and
precision of the results. Interestingly, only a few frequencies were
required to achieve accurate results on the mass and radius. For the
age the same was true when at least one l = 2 mode was considered.
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Title: The TESS Mission Target Selection Procedure
Authors: Fausnaugh, Michael; Morgan, Ed; Vanderspek, Roland; Pepper,
Joshua; Burke, Christopher J.; Levine, Alan M.; Rudat, Alexander;
Villaseñor, Jesus Noel S.; Vezie, Michael; Goeke, Robert F.; Ricker,
George R.; Latham, David W.; Seager, S.; Winn, Joshua N.; Jenkins,
Jon M.; Bakos, G. Á.; Barclay, Thomas; Berta-Thompson, Zachory K.;
Bouma, Luke G.; Boyd, Patricia T.; Brasseur, C. E.; Burt, Jennifer;
Caldwell, Douglas A.; Charbonneau, David; Christensen-Dalsgaard, J.;
Clampin, Mark; Collins, Karen A.; Colón, Knicole D.; De Lee, Nathan;
Dunham, Edward; Fleming, Scott W.; Fong, William; Garcia Soto, Aylin;
Scott Gaudi, B.; Guerrero, Natalia M.; Hesse, Katharine; Holman,
Matthew J.; Huang, Chelsea X.; Kaltenegger, Lisa; Lissauer, Jack J.;
McDermott, Scott; McLean, Brian; Mireles, Ismael; Mullally, Susan E.;
Oelkers, Ryan J.; Paegert, Martin; Pál, András; Quintana, Elisa V.;
Rinehart, S. A.; Rodriguez, David R.; Rose, Mark; Sasselov, Dimitar D.;
Schlieder, Joshua E.; Sha, Lizhou; Shporer, Avi; Smith, Jeffrey C.;
Stassun, Keivan G.; Tenenbaum, Peter; Ting, Eric B.; Torres, Guillermo;
Twicken, Joseph D.; Vanderburg, Andrew; Wohler, Bill; Yu, Liang
2021PASP..133i5002F Altcode: 2021arXiv210902665F
We describe the target selection procedure by which stars are selected
for 2 minute and 20 s observations by TESS. We first list the technical
requirements of the TESS instrument and ground systems processing that
limit the total number of target slots. We then describe algorithms
used by the TESS Payload Operation Center (POC) to merge candidate
targets requested by the various TESS mission elements (the Target
Selection Working Group, TESS Asteroseismic Science Consortium, and
Guest Investigator office). Lastly, we summarize the properties of
the observed TESS targets over the two-year primary TESS mission. We
find that the POC target selection algorithm results in 2.1-3.4 times
as many observed targets as target slots allocated for each mission
element. We also find that the sky distribution of observed targets
is different from the sky distributions of candidate targets due to
technical constraints that require a relatively even distribution of
targets across the TESS fields of view. We caution researchers exploring
statistical analyses of TESS planet-host stars that the population of
observed targets cannot be characterized by any simple set of criteria
applied to the properties of the input Candidate Target Lists.
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Title: Asteroseismic Inference of the Central Structure in a
Subgiant Star
Authors: Bellinger, Earl P.; Basu, Sarbani; Hekker, Saskia;
Christensen-Dalsgaard, Jørgen; Ball, Warrick H.
2021ApJ...915..100B Altcode: 2021arXiv210504564B
Asteroseismic measurements enable inferences of the underlying stellar
structure, such as the density and the speed of sound at various points
within the interior of the star. This provides an opportunity to test
stellar evolution theory by assessing whether the predicted structure
of a star agrees with the measured structure. Thus far, this kind of
inverse analysis has only been applied to the Sun and three solar-like
main-sequence stars. Here we extend the technique to stars on the
subgiant branch, and apply it to one of the best-characterized subgiants
of the Kepler mission, HR 7322. The observation of mixed oscillation
modes in this star facilitates inferences of the conditions of its inert
helium core, nuclear-burning hydrogen shell, and the deeper parts of
its radiative envelope. We find that despite significant differences
in the mode frequencies, the structure near to the center of this star
does not differ significantly from the predicted structure.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Oscillations in red giants from
TESS data (Silva+, 2020)
Authors: Silva Aguirre, V.; Stello, D.; Stokholm, A.; Mosumgaard,
J. R.; Ball, W. H.; Basu, S.; Bossini, D.; Bugnet, L.; Buzasi, D.;
Campante, T. L.; Carboneau, L.; Chaplin, W. J.; Corsaro, E.; Davies,
G. R.; Elsworth, Y.; Garcia, R. A.; Gaulme, P.; Hall, O. J.; Handberg,
R.; Hon, M.; Kallinger, T.; Kang, L.; Lund, M. N.; Mathur, S.; Mints,
A.; Mosser, B.; Celik Orhan, Z.; Rodrigues, T. S.; Vrard, M.; Yildiz,
M.; Zinn, J. C.; Ortel, S.; Beck, P. G.; Bell, K. J.; Guo, Z.; Jiang,
C.; Kuszlewicz, J. S.; Kuehn, C. A.; Li, T.; Lundkvist, M. S.;
Pinsonneault, M.; Tayar, J.; Cunha, M. S.; Hekker, S.; Huber, D.;
Miglio, A.; Monteiro, M. J. P. F. G.; Slumstrup, D.; Winther, M. L.;
Angelou, G.; Benomar, O.; Bodi, A.; de Moura, B. L.; Deheuvels, S.;
Derekas, A.; di Mauro, M. P.; Dupret, M. -A.; Jimenez, A.; Lebreton,
Y.; Matthews, J.; Nardetto, N.; Do Nascimento, J. D.; Pereira, F.;
Rodriguez Diaz, L. F.; Serenelli, A. M.; Spitoni, E.; Stonkute, E.;
Suarez, J. C.; Szabo, R.; van Eylen, V.; Ventura, R.; Verma, K.;
Weiss, A.; Wu, T.; Barclay, T.; Christensen-Dalsgaard, J.; Jenkins,
J. M.; Kjeldsen, H.; Ricker, G. R.; Seager, S.; Vanderspek, R.
2021yCat..18899034S Altcode:
Since the onset of the "space revolution" of high-precision high-cadence
photometry, asteroseismology has been demonstrated as a powerful tool
for informing Galactic archeology investigations. The launch of the
NASA Transiting Exoplanet Survey Satellite (TESS) mission has enabled
seismic-based inferences to go full sky-providing a clear advantage for
large ensemble studies of the different Milky Way components. Here we
demonstrate its potential for investigating the Galaxy by carrying out
the first asteroseismic ensemble study of red giant stars observed by
TESS. We use a sample of 25 stars for which we measure their global
asteroseimic observables and estimate their fundamental stellar
properties, such as radius, mass, and age. Significant improvements
are seen in the uncertainties of our estimates when combining seismic
observables from TESS with astrometric measurements from the Gaia
mission compared to when the seismology and astrometry are applied
separately. Specifically, when combined we show that stellar radii can
be determined to a precision of a few percent, masses to 5%-10%, and
ages to the 20% level. This is comparable to the precision typically
obtained using end-of-mission Kepler data. <P />(1 data file).
---------------------------------------------------------
Title: A comprehensive look at RR Lyrae stars through high-precision
photometry and astrometry
Authors: Molnár, László; Bódi, Attila; Pál, András; Bhardwaj,
Anupam; Hambsch, Franz-Josef; Benkő, József; Derekas, Aliz; Ebadi,
Mohammad; Joyce, Meridith; Hasanzadeh, Amir; Kolenberg, Katrien; Lund,
Michael B.; Nemec, James N.; Netzel, Henryka; Ngeow, Chow-Choong;
Pepper, Joshua; Plachy, Emese; Prudil, Zdenek; Siverd, Robert J.;
Skarka, Marek; Smolec, Radek; Sódor, Ádám; Sylla, Salma; Szabó,
Pál; Szabó, Róbert; Kjeldsen, Hans; Christensen-Dalsgaard, Jørgen;
Ricker, George R.
2021tsc2.confE..41M Altcode:
The TESS and Gaia missions are both collecting data of exquisite
quality for RR Lyrae-type pulsating stars. We combine light curve
shape information from TESS with distances and brightnesses from Gaia
to build a detailed classification scheme that is able to filter out
intrinsically fainter binaries and rotational variables as well as
short-period Cepheids that otherwise have light curves very similar
to that of RR Lyrae stars, while preserving targets with unusual
light curve shapes. We build a clean sample from the RR Lyrae stars
in the vicinity of the Sun, out to 5-10 kpc distances. Based on the
TESS light curves we find that a large fraction of RR Lyrae stars
exhibit various additional low-amplitude modes. The distribution of
extra modes in period is markedly different from that of stars within
the bulge and globular clusters, signaling a metallicity dependence in
the mode periods and excitation mechanisms. We also detect a possible
dependence of extra modes from color and hence effective temperatures
in overtone RRc stars. While these new results have brought us closer
to true asteroseismic analysis of RR Lyrae stars, we show through new
échelle-type diagrams that mode identification is still hindered by
the strong influence of the radial mode(s) dominating the pulsation.
---------------------------------------------------------
Title: VizieR Online Data Catalog: TESS observations of Cepheid stars
(Plachy+, 2021)
Authors: Plachy, E.; Pal, A.; Bodi, A.; Szabo, P.; Molnar, L.;
Szabados, L.; Benko, J. M.; Anderson, R. I.; Bellinger, E. P.;
Bhardwaj, A.; Ebadi, M.; Gazeas, K.; Hambsch, F. -J.; Hasanzadeh,
A.; Jurkovic, M. I.; Kalaee, M. J.; Kervella, P.; Kolenberg, K.;
Mikolajczyk, P.; Nardetto, N.; Nemec, J. M.; Netzel, H.; Ngeow, C. -C.;
Ozuyar, D.; Pascual-Granado, J.; Pilecki, B.; Ripepi, V.; Skarka, M.;
Smolec, R.; Sodor, A.; Szabo, R.; Christensen-Dalsgaard, J.; Jenkins,
J. M.; Kjeldsen, H.; Ricker, G. R.; Vanderspek, R.
2021yCat..22530011P Altcode:
The NASA Transiting Exoplanet Survey Satellite (TESS) observations
consist of ~27 day long measurements with constant pointing to a
24°x96° field of view, called a "sector". In this paper, we present
the first results on Cepheid stars observed with TESS, covering the
first five out of 26 sectors of its primary 2yr near all-sky mission
(2018-2019). <P />(3 data files).
---------------------------------------------------------
Title: VizieR Online Data Catalog: 117 exoplanets in habitable zone
with Kepler DR25 (Bryson+, 2021)
Authors: Bryson, S.; Kunimoto, M.; Kopparapu, R. K.; Coughlin, J. L.;
Borucki, W. J.; Koch, D.; Aguirre, V. S.; Allen, C.; Barentsen, G.;
Batalha, N. M.; Berger, T.; Boss, A.; Buchhave, L. A.; Burke, C. J.;
Caldwell, D. A.; Campbell, J. R.; Catanzarite, J.; Chandrasekaran,
H.; Chaplin, W. J.; Christiansen, J. L.; Christensen-Dalsgaard,
J.; Ciardi, D. R.; Clarke, B. D.; Cochran, W. D.; Dotson, J. L.;
Doyle, L. R.; Duarte, E. S.; Dunham, E. W.; Dupree, A. K.; Endl, M.;
Fanson, J. L.; Ford, E. B.; Fujieh, M.; Gautier, T. N., III; Geary,
J. C.; Gilliland, R. L.; Girouard, F. R.; Gould, A.; Haas, M. R.;
Henze, C. E.; Holman, M. J.; Howard, A. W.; Howell, S. B.; Huber,
D.; Hunter, R. C.; Jenkins, J. M.; Kjeldsen, H.; Kolodziejczak, J.;
Larson, K.; Latham, D. W.; Li, J.; Mathur, S.; Meibom, S.; Middour,
C.; Morris, R. L.; Morton, T. D.; Mullally, F.; Mullally, S. E.;
Pletcher, D.; Prsa, A.; Quinn, S. N.; Quintana, E. V.; Ragozzine,
D.; Ramirez, S. V.; Sanderfer, D. T.; Sasselov, D.; Seader, S. E.;
Shabram, M.; Shporer, A.; Smith, J. C.; Steffen, J. H.; Still, M.;
Torres, G.; Troeltzsch, J.; Twicken, J. D.; Uddin, A. K.; van Cleve,
J. E.; Voss, J.; Weiss, L. M.; Welsh, W. F.; Wohler, B.; Zamudio, K. A.
2021yCat..51610036B Altcode:
We present the occurrence rates for rocky planets in the habitable
zones (HZs) of main-sequence dwarf stars based on the Kepler DR25
planet candidate catalog and Gaia-based stellar properties. We
provide the first analysis in terms of star-dependent instellation
flux, which allows us to track HZ planets. We define {eta}{Earth}
as the HZ occurrence of planets with radii between 0.5 and 1.5
R{Earth} orbiting stars with effective temperatures between 4800
and 6300K. We find that {eta}{Earth} for the conservative HZ is
between 0.37<SUB>-0.21</SUB><SUP>+0.48</SUP> (errors reflect 68%
credible intervals) and 0.60<SUB>-0.36</SUB><SUP>+0.90</SUP>
planets per star, while the optimistic HZ occurrence
is between 0.58<SUB>-0.33</SUB><SUP>+0.73</SUP> and
0.88<SUB>-0.51</SUB><SUP>+1.28</SUP> planets per star. These
bounds reflect two extreme assumptions about the extrapolation of
completeness beyond orbital periods where DR25 completeness data are
available. The large uncertainties are due to the small number of
detected small HZ planets. We find similar occurrence rates between
using Poisson likelihood Bayesian analysis and using Approximate
Bayesian Computation. Our results are corrected for catalog completeness
and reliability. Both completeness and the planet occurrence rate are
dependent on stellar effective temperature. We also present occurrence
rates for various stellar populations and planet size ranges. We
estimate with 95% confidence that, on average, the nearest HZ planet
around G and K dwarfs is ~6pc away and there are ~4 HZ rocky planets
around G and K dwarfs within 10pc of the Sun. <P />(1 data file).
---------------------------------------------------------
Title: TESS Observations of Cepheid Stars: First Light Results
Authors: Plachy, E.; Pál, A.; Bódi, A.; Szabó, P.; Molnár, L.;
Szabados, L.; Benkő, J. M.; Anderson, R. I.; Bellinger, E. P.;
Bhardwaj, A.; Ebadi, M.; Gazeas, K.; Hambsch, F. -J.; Hasanzadeh,
A.; Jurkovic, M. I.; Kalaee, M. J.; Kervella, P.; Kolenberg, K.;
Mikołajczyk, P.; Nardetto, N.; Nemec, J. M.; Netzel, H.; Ngeow,
C. -C.; Ozuyar, D.; Pascual-Granado, J.; Pilecki, B.; Ripepi, V.;
Skarka, M.; Smolec, R.; Sódor, Á.; Szabó, R.; Christensen-Dalsgaard,
J.; Jenkins, J. M.; Kjeldsen, H.; Ricker, G. R.; Vanderspek, R.
2021ApJS..253...11P Altcode: 2020arXiv201209709P
We present the first analysis of Cepheid stars observed by the TESS
space mission in Sectors 1-5. Our sample consists of 25 pulsators:
ten fundamental mode, three overtone and two double-mode classical
Cepheids, plus three type II and seven anomalous Cepheids. The targets
were chosen from fields with different stellar densities, both from
the Galactic field and from the Magellanic System. Three targets have 2
minutes cadence light curves available by the TESS Science Processing
Operations Center: for the rest, we prepared custom light curves
from the full-frame images with our own differential photometric FITSH
pipeline. Our main goal was to explore the potential and the limitations
of TESS concerning the various subtypes of Cepheids. We detected many
low-amplitude features: weak modulation, period jitter, and timing
variations due to light-time effect. We also report signs of nonradial
modes and the first discovery of such a mode in an anomalous Cepheid,
the overtone star XZ Cet, which we then confirmed with ground-based
multicolor photometric measurements. We prepared a custom photometric
solution to minimize saturation effects in the bright fundamental-mode
classical Cepheid, β Dor with the lightkurve software, and we revealed
strong evidence of cycle-to-cycle variations in the star. In several
cases, however, fluctuations in the pulsation could not be distinguished
from instrumental effects, such as contamination from nearby sources,
which also varies between sectors. Finally, we discuss how precise
light-curve shapes will be crucial not only for classification purposes
but also to determine physical properties of these stars.
---------------------------------------------------------
Title: The Occurrence of Rocky Habitable-zone Planets around
Solar-like Stars from Kepler Data
Authors: Bryson, Steve; Kunimoto, Michelle; Kopparapu, Ravi K.;
Coughlin, Jeffrey L.; Borucki, William J.; Koch, David; Aguirre,
Victor Silva; Allen, Christopher; Barentsen, Geert; Batalha, Natalie
M.; Berger, Travis; Boss, Alan; Buchhave, Lars A.; Burke, Christopher
J.; Caldwell, Douglas A.; Campbell, Jennifer R.; Catanzarite, Joseph;
Chandrasekaran, Hema; Chaplin, William J.; Christiansen, Jessie L.;
Christensen-Dalsgaard, Jørgen; Ciardi, David R.; Clarke, Bruce D.;
Cochran, William D.; Dotson, Jessie L.; Doyle, Laurance R.; Duarte,
Eduardo Seperuelo; Dunham, Edward W.; Dupree, Andrea K.; Endl, Michael;
Fanson, James L.; Ford, Eric B.; Fujieh, Maura; Gautier, Thomas N.,
III; Geary, John C.; Gilliland, Ronald L.; Girouard, Forrest R.; Gould,
Alan; Haas, Michael R.; Henze, Christopher E.; Holman, Matthew J.;
Howard, Andrew W.; Howell, Steve B.; Huber, Daniel; Hunter, Roger C.;
Jenkins, Jon M.; Kjeldsen, Hans; Kolodziejczak, Jeffery; Larson,
Kipp; Latham, David W.; Li, Jie; Mathur, Savita; Meibom, Søren;
Middour, Chris; Morris, Robert L.; Morton, Timothy D.; Mullally,
Fergal; Mullally, Susan E.; Pletcher, David; Prsa, Andrej; Quinn,
Samuel N.; Quintana, Elisa V.; Ragozzine, Darin; Ramirez, Solange V.;
Sanderfer, Dwight T.; Sasselov, Dimitar; Seader, Shawn E.; Shabram,
Megan; Shporer, Avi; Smith, Jeffrey C.; Steffen, Jason H.; Still,
Martin; Torres, Guillermo; Troeltzsch, John; Twicken, Joseph D.;
Uddin, Akm Kamal; Van Cleve, Jeffrey E.; Voss, Janice; Weiss, Lauren
M.; Welsh, William F.; Wohler, Bill; Zamudio, Khadeejah A.
2021AJ....161...36B Altcode: 2020arXiv201014812B
We present the occurrence rates for rocky planets in the habitable
zones (HZs) of main-sequence dwarf stars based on the Kepler DR25
planet candidate catalog and Gaia-based stellar properties. We provide
the first analysis in terms of star-dependent instellation flux,
which allows us to track HZ planets. We define η<SUB>⊕</SUB>
as the HZ occurrence of planets with radii between 0.5 and 1.5
R<SUB>⊕</SUB> orbiting stars with effective temperatures between
4800 and 6300 K. We find that η<SUB>⊕</SUB> for the conservative
HZ is between ${0.37}_{-0.21}^{+0.48}$ (errors reflect 68% credible
intervals) and ${0.60}_{-0.36}^{+0.90}$ planets per star, while the
optimistic HZ occurrence is between ${0.58}_{-0.33}^{+0.73}$ and
${0.88}_{-0.51}^{+1.28}$ planets per star. These bounds reflect two
extreme assumptions about the extrapolation of completeness beyond
orbital periods where DR25 completeness data are available. The
large uncertainties are due to the small number of detected
small HZ planets. We find similar occurrence rates between using
Poisson likelihood Bayesian analysis and using Approximate Bayesian
Computation. Our results are corrected for catalog completeness and
reliability. Both completeness and the planet occurrence rate are
dependent on stellar effective temperature. We also present occurrence
rates for various stellar populations and planet size ranges. We
estimate with 95% confidence that, on average, the nearest HZ planet
around G and K dwarfs is ∼6 pc away and there are ∼4 HZ rocky
planets around G and K dwarfs within 10 pc of the Sun.
---------------------------------------------------------
Title: Seismic solar models from Ledoux discriminant inversions
Authors: Buldgen, G.; Eggenberger, P.; Baturin, V. A.; Corbard, T.;
Christensen-Dalsgaard, J.; Salmon, S. J. A. J.; Noels, A.; Oreshina,
A. V.; Scuflaire, R.
2020A&A...642A..36B Altcode: 2020arXiv200710222B
Context. The Sun constitutes an excellent laboratory of fundamental
physics. With the advent of helioseismology, we were able to probe its
internal layers with unprecendented precision and thoroughness. However,
the current state of solar modelling is still stained by tedious
issues. One of these central problems is related to the disagreement
between models computed with recent photospheric abundances and
helioseismic constraints. The observed discrepancies raise questions
on some fundamental ingredients entering the computation of solar and
stellar evolution models. <BR /> Aims: We used solar evolutionary models
as initial conditions for reintegrating their structure using Ledoux
discriminant inversions. The resulting models are defined as seismic
solar models, satisfying the equations of hydrostatic equilibrium. These
seismic models will allow us to better constrain the internal structure
of the Sun and provide complementary information to that of calibrated
standard and non-standard models. <BR /> Methods: We used inversions of
the Ledoux discriminant to reintegrate seismic solar models satisfying
the equations of hydrostatic equilibrium. These seismic models were
computed using various reference models with different equations of
state, abundances, and opacity tables. We checked the robustness of
our approach by confirming the good agreement of our seismic models in
terms of sound speed, density, and entropy proxy inversions, as well
as frequency-separation ratios of low-degree pressure modes. <BR />
Results: Our method allows us to determine the Ledoux discriminant
profile of the Sun with an excellent accuracy and compute full profiles
of this quantity. Our seismic models show an agreement with seismic
data of ≈0.1% in sound speed, density, and entropy proxy after seven
iterations in addition to an excellent agreement with the observed
frequency-separation ratios. They surpass all standard and non-standard
evolutionary models including ad hoc modifications of their physical
ingredients that aim to reproduce helioseismic constraints. <BR />
Conclusions: The obtained seismic Ledoux discriminant profile, as
well as the full consistent structure obtained from our reconstruction
procedure paves the way for renewed attempts at constraining the solar
modelling problem and the missing physical processes acting in the solar
interior by breaking free from the hypotheses of evolutionary models.
---------------------------------------------------------
Title: Erratum: Variations of the mixing character of dipolar mixed
modes in red giant stars
Authors: Jiang, C.; Cunha, M.; Christensen-Dalsgaard, J.; Zhang, Q. S.
2020MNRAS.497..167J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: High-precision abundances of elements in solar-type
stars. Evidence of two distinct sequences in abundance-age relations
Authors: Nissen, P. E.; Christensen-Dalsgaard, J.; Mosumgaard, J. R.;
Silva Aguirre, V.; Spitoni, E.; Verma, K.
2020A&A...640A..81N Altcode: 2020arXiv200606013N
<BR /> Aims: Previous high-precision studies of abundances of elements
in solar twin stars are extended to a wider metallicity range to see how
the trends of element ratios with stellar age depend on [Fe/H]. <BR />
Methods: HARPS spectra with signal-to-noise ratios S/N ≳ 600 at λ
∼ 6000 Å were analysed with MARCS model atmospheres to obtain 1D
LTE abundances of C, O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Sr, and Y
for 72 nearby solar-type stars with metallicities in the range of -0.3
≲ [Fe/H] ≲ +0.3 and ASTEC stellar models were used to determine
stellar ages from effective temperatures, luminosities obtained via
Gaia DR2 parallaxes, and heavy element abundances. <BR /> Results:
The age-metallicity distribution appears to consist of the following
two distinct populations: a sequence of old stars with a steep rise of
[Fe/H] to ∼ + 0.3 dex at an age of ∼7 Gyr and a younger sequence
with [Fe/H] increasing from about -0.3 dex to ∼ + 0.2 dex over
the last 6 Gyr. Furthermore, the trends of several abundance ratios,
[O/Fe], [Na/Fe], [Ca/Fe], and [Ni/Fe], as a function of stellar age,
split into two corresponding sequences. The [Y/Mg]-age relation, on
the other hand, shows no offset between the two age sequences and has
no significant dependence on [Fe/H], but the components of a visual
binary star, ζ Reticuli, have a large and puzzling deviation. <BR
/> Conclusions: The split of the age-metallicity distribution into
two sequences may be interpreted as evidence of two episodes of
accretion of gas onto the Galactic disk with a quenching of star
formation in between. Some of the [X/Fe]-age relations support this
scenario but other relations are not so easy to explain, which calls
for a deeper study of systematic errors in the derived abundances
as a function of [Fe/H], in particular 3D non-LTE effects. <P />Full
Tables 1 and 2 are only available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/640/A81">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/640/A81</A>
---------------------------------------------------------
Title: Asteroseismology of 36 Kepler subgiants - II. Determining
ages from detailed modelling
Authors: Li, Tanda; Bedding, Timothy R.; Christensen-Dalsgaard,
Jørgen; Stello, Dennis; Li, Yaguang; Keen, Matthew A.
2020MNRAS.495.3431L Altcode: 2020arXiv200600901L; 2020MNRAS.tmp.1467L
Detailed modelling of stellar oscillations is able to give precise
estimates for stellar ages, but the inferred results typically depend on
the adopted model parameters used for the age inference. High-quality
asteroseismic data with precise measurements of mixed modes are
available for 36 Kepler subgiants. To obtain a handle on the robustness
of the ages for these stars, we first study the dependencies of
seismic ages on three model input parameters. We find that inferred
ages do not change systematically with the helium fraction (Y) or
the mixing-length parameter (α<SUB>MLT</SUB>) but depend strongly on
the metallicity ([M/H]) of the model. The results indicate that age
estimates of subgiants have less model dependence and hence are more
reliable than those of main-sequence stars or red giants. We then model
individual oscillation frequencies of the same 36 Kepler subgiants,
using observed metallicities, and obtain their ages with an average
precision of ∼15 per cent. The comparison with previous age estimates
with different stellar codes or input physics shows good agreement
(mostly within 2σ). We hence suggest that seismology-determined ages
of subgiants are not greatly model dependent.
---------------------------------------------------------
Title: Variations of the mixing character of dipolar mixed modes in
red giant stars
Authors: Jiang, C.; Cunha, M.; Christensen-Dalsgaard, J.; Zhang, QS
2020MNRAS.495..621J Altcode: 2020MNRAS.tmp.1405J; 2020arXiv200501464J
Because of the high-quality data of space missions, the detection of
mixed modes has become possible in numerous stars. In this work, we
investigate how the mixing character of dipolar mixed modes changes
with stellar evolution, as well as with frequency within each stellar
model. This is achieved by monitoring the variations in the coupling
strength and the period spacing of dipolar mixed modes in red-giant
models. These parameters are measured by fitting the asymptotic
expansion of mixed modes to the model frequencies of a grid of
red-giant models with masses between 1.0 and 2.0 M<SUB>⊙</SUB>
and three different chemical abundances. The coupling strength and
the period spacing decrease with stellar evolution. We find that the
slopes of their decreasing trends depend on the radial order of the
pressure mode component. A non-negligible increase of the coupling
strength with frequency by up to around 40 per cent is found in the
observable frequency range for a set of red-giant models. On the
contrary, no significant changes of the period spacing with frequency
are found. The changes in the mixing character of the modes are in most
cases affected by the model mass and metallicity. Buoyancy glitches
also have an impact on the mixing character. Significant fluctuations
in the estimated coupling strength and period spacing are found for
models approaching the luminosity bump, if the glitch impact of the
frequencies is not considered in the applied asymptotic expansion.
---------------------------------------------------------
Title: TESS Asteroseismic Analysis of the Known Exoplanet Host Star
HD 222076
Authors: Jiang, Chen; Bedding, Timothy R.; Stassun, Keivan G.; Veras,
Dimitri; Corsaro, Enrico; Buzasi, Derek L.; Mikołajczyk, Przemysław;
Zhang, Qian-sheng; Ou, Jian-wen; Campante, Tiago L.; Rodrigues,
Thaíise S.; Nsamba, Benard; Bossini, Diego; Kane, Stephen R.; Ong,
Jia Mian Joel; Yıldız, Mutlu; Çelik Orhan, Zeynep; Örtel, Sibel;
Wu, Tao; Zhang, Xinyi; Li, Tanda; Basu, Sarbani; Cunha, Margarida S.;
Christensen-Dalsgaard, Jørgen; Chaplin, William J.
2020ApJ...896...65J Altcode: 2020arXiv200500272J
The Transiting Exoplanet Survey Satellite (TESS) is an all-sky
survey mission aiming to search for exoplanets that transit bright
stars. The high-quality photometric data of TESS are excellent
for the asteroseismic study of solar-like stars. In this work, we
present an asteroseismic analysis of the red-giant star HD 222076
hosting a long-period (2.4 yr) giant planet discovered through radial
velocities. Solar-like oscillations of HD 222076 are detected around
203 μHz by TESS for the first time. Asteroseismic modeling, using
global asteroseismic parameters as inputs, yields a determination
of the stellar mass ( ${M}_{\star }=1.12\pm 0.12\,{M}_{\odot }$ ),
radius ( ${R}_{\star }=4.34\pm 0.21\,{R}_{\odot }$ ), and age (7.4 ±
2.7 Gyr), with precisions greatly improved from previous studies. The
period spacing of the dipolar mixed modes extracted from the observed
power spectrum reveals that the star is on the red-giant branch burning
hydrogen in a shell surrounding the core. We find that the planet will
not escape the tidal pull of the star and will be engulfed into it
within about 800 Myr, before the tip of the red-giant branch is reached.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Abundances of 72 solar-type stars
(Nissen+, 2020)
Authors: Nissen, P. E.; Christensen-Dalsgaard, J.; Mosumgaard, J. R.;
Silva Aguirre, V.; Spitoni, E.; Verma, K.
2020yCat..36400081N Altcode:
Stellar parameters are given in Table 1 and abundance ratios with
respect to Fe in Table 2. <P />(2 data files).
---------------------------------------------------------
Title: Doppler Imaging and Differential Rotation of σ<SUP>2</SUP>
Coronae Borealis Using SONG
Authors: Xiang, Yue; Gu, Shenghong; Cameron, A. Collier; Barnes, J. R.;
Christensen-Dalsgaard, J.; Grundahl, F.; Antoci, V.; Andersen, M. F.;
Pallé, P. L.
2020ApJ...893..164X Altcode: 2020arXiv200502592X
We present new Doppler images of both components of the double-lined
binary σ<SUP>2</SUP> CrB, based on the high-resolution spectroscopic
data collected during 11 nights in 2015 March-April. The observed
spectra form two independent data sets with sufficient phase
coverage. We apply the least-squares deconvolution to all observed
spectra to obtain high signal-to-noise mean profiles, from which
we derive the Doppler images of both components of σ<SUP>2</SUP>
CrB simultaneously. The surfaces of both F9 and G0 components are
dominated by pronounced polar spots. The F9 component exhibits a weak
spot at latitude 30° and its mid-to-low latitudes are relatively
featureless. The G0 star shows an extended spot structure at latitude
30°, and its surface spot coverage is larger than that of the F9
star, which suggests a higher level of magnetic activity. With the
cross-correlation method, we derive a solar-like surface differential
rotation on the G0 star of σ<SUP>2</SUP> CrB for the first time, and
the surface shear rate is ΔΩ = 0.180 ± 0.004 rad days<SUP>-1</SUP>
and α = ΔΩ/Ω<SUB>eq</SUB> = 0.032 ± 0.001. We do not obtain a clear
surface shear law for the F9 star due to the lack of mid-to-low latitude
features, but detect a systematic longitude shift of high-latitude
spots, which indicates a slower rotation with respect to the corotating
frame.
---------------------------------------------------------
Title: The Aarhus red giants challenge. I. Stellar structures in
the red giant branch phase
Authors: Silva Aguirre, V.; Christensen-Dalsgaard, J.; Cassisi, S.;
Miller Bertolami, M.; Serenelli, A.; Stello, D.; Weiss, A.; Angelou,
G.; Jiang, C.; Lebreton, Y.; Spada, F.; Bellinger, E. P.; Deheuvels,
S.; Ouazzani, R. M.; Pietrinferni, A.; Mosumgaard, J. R.; Townsend,
R. H. D.; Battich, T.; Bossini, D.; Constantino, T.; Eggenberger,
P.; Hekker, S.; Mazumdar, A.; Miglio, A.; Nielsen, K. B.; Salaris, M.
2020A&A...635A.164S Altcode: 2019arXiv191204909S
Context. With the advent of space-based asteroseismology, determining
accurate properties of red-giant stars using their observed oscillations
has become the focus of many investigations due to their implications
in a variety of fields in astrophysics. Stellar models are fundamental
in predicting quantities such as stellar age, and their reliability
critically depends on the numerical implementation of the physics at
play in this evolutionary phase. <BR /> Aims: We introduce the Aarhus
red giants challenge, a series of detailed comparisons between widely
used stellar evolution and oscillation codes that aim to establish
the minimum level of uncertainties in properties of red giants
arising solely from numerical implementations. We present the first
set of results focusing on stellar evolution tracks and structures
in the red-giant-branch (RGB) phase. <BR /> Methods: Using nine
state-of-the-art stellar evolution codes, we defined a set of input
physics and physical constants for our calculations and calibrated
the convective efficiency to a specific point on the main sequence. We
produced evolutionary tracks and stellar structure models at a fixed
radius along the red-giant branch for masses of 1.0 M<SUB>⊙</SUB>,
1.5 M<SUB>⊙</SUB>, 2.0 M<SUB>⊙</SUB>, and 2.5 M<SUB>⊙</SUB>, and
compared the predicted stellar properties. <BR /> Results: Once models
have been calibrated on the main sequence, we find a residual spread
in the predicted effective temperatures across all codes of ∼20 K at
solar radius and ∼30-40 K in the RGB regardless of the considered
stellar mass. The predicted ages show variations of 2-5% (increasing
with stellar mass), which we attribute to differences in the numerical
implementation of energy generation. The luminosity of the RGB-bump
shows a spread of about 10% for the considered codes, which translates
into magnitude differences of ∼0.1 mag in the optical V-band. We also
compare the predicted [C/N] abundance ratio and find a spread of 0.1 dex
or more for all considered masses. <BR /> Conclusions: Our comparisons
show that differences at the level of a few percent still remain in
evolutionary calculations of red giants branch stars despite the use
of the same input physics. These are mostly due to differences in the
energy generation routines and interpolation across opacities, and they
call for further investigation on these matters in the context of using
properties of red giants as benchmarks for astrophysical studies. <P
/>All our evolutionary calculations and models are available at <A
href="https://github.com/vsilvagui/aarhus_RG_challenge">https://github.com/vsilvagui/aarhus_RG_challenge</A>
---------------------------------------------------------
Title: The Aarhus red giants challenge. II. Stellar oscillations in
the red giant branch phase
Authors: Christensen-Dalsgaard, J.; Silva Aguirre, V.; Cassisi, S.;
Miller Bertolami, M.; Serenelli, A.; Stello, D.; Weiss, A.; Angelou,
G.; Jiang, C.; Lebreton, Y.; Spada, F.; Bellinger, E. P.; Deheuvels,
S.; Ouazzani, R. M.; Pietrinferni, A.; Mosumgaard, J. R.; Townsend,
R. H. D.; Battich, T.; Bossini, D.; Constantino, T.; Eggenberger,
P.; Hekker, S.; Mazumdar, A.; Miglio, A.; Nielsen, K. B.; Salaris, M.
2020A&A...635A.165C Altcode: 2020arXiv200202816C
Contact. The large quantity of high-quality asteroseismic data that have
been obtained from space-based photometric missions and the accuracy
of the resulting frequencies motivate a careful consideration of the
accuracy of computed oscillation frequencies of stellar models, when
applied as diagnostics of the model properties. <BR /> Aims: Based
on models of red-giant stars that have been independently calculated
using different stellar evolution codes, we investigate the extent
to which the differences in the model calculation affect the model
oscillation frequencies and other asteroseismic diagnostics. <BR />
Methods: For each of the models, which cover four different masses and
different evolution stages on the red-giant branch, we computed full
sets of low-degree oscillation frequencies using a single pulsation
code and, from these frequencies, typical asteroseismic diagnostics. In
addition, we carried out preliminary analyses to relate differences in
the oscillation properties to the corresponding model differences. <BR
/> Results: In general, the differences in asteroseismic properties
between the different models greatly exceed the observational precision
of these properties. This is particularly true for the nonradial modes
whose mixed acoustic and gravity-wave character makes them sensitive
to the structure of the deep stellar interior and, hence, to details
of their evolution. In some cases, identifying these differences led
to improvements in the final models presented here and in Paper I;
here we illustrate particular examples of this. <BR /> Conclusions:
Further improvements in stellar modelling are required in order fully
to utilise the observational accuracy to probe intrinsic limitations
in the modelling and improve our understanding of stellar internal
physics. However, our analysis of the frequency differences and their
relation to stellar internal properties provides a striking illustration
of the potential, in particular, of the mixed modes of red-giant stars
for the diagnostics of stellar interiors.
---------------------------------------------------------
Title: Detection and Characterization of Oscillating Red Giants:
First Results from the TESS Satellite
Authors: Silva Aguirre, Víctor; Stello, Dennis; Stokholm, Amalie;
Mosumgaard, Jakob R.; Ball, Warrick H.; Basu, Sarbani; Bossini, Diego;
Bugnet, Lisa; Buzasi, Derek; Campante, Tiago L.; Carboneau, Lindsey;
Chaplin, William J.; Corsaro, Enrico; Davies, Guy R.; Elsworth, Yvonne;
García, Rafael A.; Gaulme, Patrick; Hall, Oliver J.; Handberg,
Rasmus; Hon, Marc; Kallinger, Thomas; Kang, Liu; Lund, Mikkel N.;
Mathur, Savita; Mints, Alexey; Mosser, Benoit; Çelik Orhan, Zeynep;
Rodrigues, Thaíse S.; Vrard, Mathieu; Yıldız, Mutlu; Zinn, Joel C.;
Örtel, Sibel; Beck, Paul G.; Bell, Keaton J.; Guo, Zhao; Jiang, Chen;
Kuszlewicz, James S.; Kuehn, Charles A.; Li, Tanda; Lundkvist, Mia S.;
Pinsonneault, Marc; Tayar, Jamie; Cunha, Margarida S.; Hekker, Saskia;
Huber, Daniel; Miglio, Andrea; F. G. Monteiro, Mario J. P.; Slumstrup,
Ditte; Winther, Mark L.; Angelou, George; Benomar, Othman; Bódi,
Attila; De Moura, Bruno L.; Deheuvels, Sébastien; Derekas, Aliz; Di
Mauro, Maria Pia; Dupret, Marc-Antoine; Jiménez, Antonio; Lebreton,
Yveline; Matthews, Jaymie; Nardetto, Nicolas; do Nascimento, Jose D.,
Jr.; Pereira, Filipe; Rodríguez Díaz, Luisa F.; Serenelli, Aldo M.;
Spitoni, Emanuele; Stonkutė, Edita; Suárez, Juan Carlos; Szabó,
Robert; Van Eylen, Vincent; Ventura, Rita; Verma, Kuldeep; Weiss,
Achim; Wu, Tao; Barclay, Thomas; Christensen-Dalsgaard, Jørgen;
Jenkins, Jon M.; Kjeldsen, Hans; Ricker, George R.; Seager, Sara;
Vanderspek, Roland
2020ApJ...889L..34S Altcode: 2019arXiv191207604S; 2020ApJ...889L..34A
Since the onset of the "space revolution" of high-precision high-cadence
photometry, asteroseismology has been demonstrated as a powerful tool
for informing Galactic archeology investigations. The launch of the
NASA Transiting Exoplanet Survey Satellite (TESS) mission has enabled
seismic-based inferences to go full sky—providing a clear advantage
for large ensemble studies of the different Milky Way components. Here
we demonstrate its potential for investigating the Galaxy by carrying
out the first asteroseismic ensemble study of red giant stars observed
by TESS. We use a sample of 25 stars for which we measure their
global asteroseimic observables and estimate their fundamental stellar
properties, such as radius, mass, and age. Significant improvements
are seen in the uncertainties of our estimates when combining seismic
observables from TESS with astrometric measurements from the Gaia
mission compared to when the seismology and astrometry are applied
separately. Specifically, when combined we show that stellar radii can
be determined to a precision of a few percent, masses to 5%-10%, and
ages to the 20% level. This is comparable to the precision typically
obtained using end-of-mission Kepler data.
---------------------------------------------------------
Title: Dynamics of the Sun and Stars; Honoring the Life and Work of
Michael J. Thompson
Authors: Monteiro, Mário J. P. F. G.; García, Rafael A.;
Christensen-Dalsgaard, Jørgen; McIntosh, Scott W.
2020ASSP...57.....M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Open Discussion
Authors: García, R. A.; Mathur, S.; Monteiro, M. J. P. F. G.;
Christensen-Dalsgaard, J.; McIntosh, S. W.
2020ASSP...57..329G Altcode:
During the last morning of the conference, a one-hour open discussion
allowed the participants to debate some of the "hot" topics presented
all along the meeting as well as on some of the key issues in the field
mostly related with the work Prof. Michael J. Thompson studied during
his carrier. The discussion covered theory and methods, current and
future modeling efforts, observations, and future instrumentation. At
the end, Dr. Robin Thompson discussed about the use of inversion
methods in his current research, of particular interest these days,
about the control of infectious disease outbreaks.
---------------------------------------------------------
Title: Coupling 1D stellar evolution with 3D-hydrodynamical
simulations on-the-fly II: stellar evolution and asteroseismic
applications
Authors: Mosumgaard, Jakob Rørsted; Jørgensen, Andreas Christ
Sølvsten; Weiss, Achim; Silva Aguirre, Víctor; Christensen-Dalsgaard,
Jørgen
2020MNRAS.491.1160M Altcode: 2019arXiv191010163M; 2019arXiv191010163R; 2019MNRAS.tmp.2585M
Models of stellar structure and evolution are an indispensable tool
in astrophysics, yet they are known to incorrectly reproduce the
outer convective layers of stars. In the first paper of this series,
we presented a novel procedure to include the mean structure of 3D
hydrodynamical simulations on-the-fly in stellar models, and found
it to significantly improve the outer stratification and oscillation
frequencies of a standard solar model. In this work, we extend the
analysis of the method; specifically how the transition point between
envelope and interior affects the models. We confirm the versatility
of our method by successfully repeating the entire procedure for a
different grid of 3D hydrosimulations. Furthermore, the applicability of
the procedure was investigated across the HR diagram and an accuracy
comparable to the solar case was found. Moreover, we explored the
implications on stellar evolution and find that the red-giant branch
is shifted about 40 K to higher effective temperatures. Finally,
we present for the first time an asteroseismic analysis based on
stellar models fully utilizing the stratification of 3D simulations
on-the-fly. These new models significantly reduce the asteroseismic
surface term for the two selected stars in the Kepler field. We extend
the analysis to red giants and characterize the shape of the surface
effect in this regime. Lastly, we stress that the interpolation required
by our method would benefit from new 3D simulations, resulting in a
finer sampling of the grid.
---------------------------------------------------------
Title: Contemplating the Future
Authors: Christensen-Dalsgaard, Jørgen
2020ASSP...57..335C Altcode:
The prospects for the further development of stellar astrophysics remain
golden. Much can still be done based on the Kepler data, the TESS
mission is providing data over most of the sky, at a 10 min cadence
in the extended phase, PLATO will provide data comparable with those
of Kepler for relatively near-by stars, ground-based observations
yield data of even higher quality for selected stars, and Gaia is
revolutionizing the determination of global stellar properties. On the
modelling side ever more realistic simulations are becoming possible
of dynamic phenomena in stellar interiors, and new techniques, known
as artificial intelligence or deep learning, are helping the analysis
of the huge amounts of data that are becoming available. Much of this
effort is aimed at applications of stellar physics in other areas
of astrophysics, such as exoplanets or Galactic archaeology. In the
excitement of these developments, in the spirit of Michael we should
not forget the basic goal of improving our physical understanding of
stars, combining human intelligence and intuition with mathematical
analysis and modelling, observations, and data interpretation. This
should be kept in mind in our work and, even more importantly, in the
education of coming generations of stellar astrophysicists.
---------------------------------------------------------
Title: A solution to the “solar abundance” problem
Authors: Zhang, Q. -S.; Li, Y.; Christensen-Dalsgaard, J.
2020svos.conf..303Z Altcode:
We report a solution to the long-standing “solar abundance”
problem. Solar models that include three extra physical processes
(convective overshoot, solar wind and PMS accretion) which are missing
from standard solar models are shown to be consistent simultaneously
with helioseismic inferences (the depth and helium abundance of the
convection zone and profiles of sound speed and density), the observed
solar Li abundance, and solar neutrino fluxes.
---------------------------------------------------------
Title: Asteroseismic signatures of the helium core flash
Authors: Miller Bertolami, M. M.; Battich, T.; Córsico, A. H.;
Christensen-Dalsgaard, J.; Althaus, L. G.
2020NatAs...4...67M Altcode: 2019NatAs.tmp..452M; 2020arXiv200502070M
All evolved stars of up to 2 solar masses undergo a helium core flash at
the end of their first stage as a giant star. Although theoretically
predicted more than 50 years ago<SUP>1,2</SUP>, this core flash
phase has yet to be observationally probed. We show here that gravity
modes stochastically excited by helium-flash-driven convection are
able to reach the stellar surface and induce periodic photometric
variabilities in hot subdwarf stars with amplitudes of the order of a
few thousandths of a magnitude. As such, they can now be detected by
space-based photometry with the Transiting Exoplanet Survey Satellite
in relatively bright stars (for example, Johnson-Cousins magnitudes of
I<SUB>C</SUB> ≲ 13 mag)<SUP>3</SUP>. The range of predicted periods
spans from a few thousand seconds to tens of thousands of seconds,
depending on the details of the excitation region. In addition, we find
that stochastically excited pulsations reproduce the pulsations observed
in a few helium-rich hot subdwarf stars. These stars, particularly
the future Transiting Exoplanet Survey Satellite target Feige 46,
are the most promising candidates to probe the helium core flash for
the first time.
---------------------------------------------------------
Title: Age dating of an early Milky Way merger via asteroseismology
of the naked-eye star ν Indi
Authors: Chaplin, William J.; Serenelli, Aldo M.; Miglio, Andrea;
Morel, Thierry; Mackereth, J. Ted; Vincenzo, Fiorenzo; Kjeldsen, Hans;
Basu, Sarbani; Ball, Warrick H.; Stokholm, Amalie; Verma, Kuldeep;
Mosumgaard, Jakob Rørsted; Silva Aguirre, Victor; Mazumdar, Anwesh;
Ranadive, Pritesh; Antia, H. M.; Lebreton, Yveline; Ong, Joel;
Appourchaux, Thierry; Bedding, Timothy R.; Christensen-Dalsgaard,
Jørgen; Creevey, Orlagh; García, Rafael A.; Handberg, Rasmus; Huber,
Daniel; Kawaler, Steven D.; Lund, Mikkel N.; Metcalfe, Travis S.;
Stassun, Keivan G.; Bazot, Michäel; Beck, Paul G.; Bell, Keaton J.;
Bergemann, Maria; Buzasi, Derek L.; Benomar, Othman; Bossini, Diego;
Bugnet, Lisa; Campante, Tiago L.; Orhan, Zeynep çelik; Corsaro,
Enrico; González-Cuesta, Lucía; Davies, Guy R.; Di Mauro, Maria
Pia; Egeland, Ricky; Elsworth, Yvonne P.; Gaulme, Patrick; Ghasemi,
Hamed; Guo, Zhao; Hall, Oliver J.; Hasanzadeh, Amir; Hekker, Saskia;
Howe, Rachel; Jenkins, Jon M.; Jiménez, Antonio; Kiefer, René;
Kuszlewicz, James S.; Kallinger, Thomas; Latham, David W.; Lundkvist,
Mia S.; Mathur, Savita; Montalbán, Josefina; Mosser, Benoit; Bedón,
Andres Moya; Nielsen, Martin Bo; Örtel, Sibel; Rendle, Ben M.; Ricker,
George R.; Rodrigues, Thaíse S.; Roxburgh, Ian W.; Safari, Hossein;
Schofield, Mathew; Seager, Sara; Smalley, Barry; Stello, Dennis;
Szabó, Róbert; Tayar, Jamie; Themeßl, Nathalie; Thomas, Alexandra
E. L.; Vanderspek, Roland K.; van Rossem, Walter E.; Vrard, Mathieu;
Weiss, Achim; White, Timothy R.; Winn, Joshua N.; Yıldız, Mutlu
2020NatAs...4..382C Altcode: 2020NatAs.tmp....7C; 2020arXiv200104653C
Over the course of its history, the Milky Way has ingested multiple
smaller satellite galaxies<SUP>1</SUP>. Although these accreted
stellar populations can be forensically identified as kinematically
distinct structures within the Galaxy, it is difficult in general
to date precisely the age at which any one merger occurred. Recent
results have revealed a population of stars that were accreted via the
collision of a dwarf galaxy, called Gaia-Enceladus<SUP>1</SUP>, leading
to substantial pollution of the chemical and dynamical properties of
the Milky Way. Here we identify the very bright, naked-eye star ν
Indi as an indicator of the age of the early in situ population of
the Galaxy. We combine asteroseismic, spectroscopic, astrometric and
kinematic observations to show that this metal-poor, alpha-element-rich
star was an indigenous member of the halo, and we measure its age
to be 11.0 ±0.7 ? (stat) ±0.8 ? (sys) billion years. The star
bears hallmarks consistent with having been kinematically heated by
the Gaia-Enceladus collision. Its age implies that the earliest the
merger could have begun was 11.6 and 13.2 billion years ago, at 68%
and 95% confidence, respectively. Computations based on hierarchical
cosmological models slightly reduce the above limits.
---------------------------------------------------------
Title: Asteroseismic Constraints on the Cosmic-time Variation of
the Gravitational Constant from an Ancient Main-sequence Star
Authors: Bellinger, Earl Patrick; Christensen-Dalsgaard, Jørgen
2019ApJ...887L...1B Altcode: 2019arXiv190906378B
We investigate the variation of the gravitational constant G
over the history of the universe by modeling the effects on the
evolution and asteroseismology of the low-mass star KIC 7970740,
which is one of the oldest (∼11 Gyr) and best-observed solar-like
oscillators in the Galaxy. From these data we find \dot{G}/G=(2.1+/-
2.9)× 10<SUP>-12</SUP> yr<SUP>-1</SUP>, that is, no evidence for
any variation in G. We also find a Bayesian asteroseismic estimate of
the age of the universe as well as astrophysical S-factors for five
nuclear reactions obtained through a 12-dimensional stellar evolution
Markov Chain Monte Carlo simulation.
---------------------------------------------------------
Title: Testing Stellar Evolution with Asteroseismic Inversions of
a Main-sequence Star Harboring a Small Convective Core
Authors: Bellinger, Earl P.; Basu, Sarbani; Hekker, Saskia;
Christensen-Dalsgaard, Jørgen
2019ApJ...885..143B Altcode: 2019arXiv191000603B
The goal of stellar evolution theory is to predict the structure
of stars throughout their lifetimes. Usually, these predictions
can be assessed only indirectly, for example by comparing predicted
and observed effective temperatures and luminosities. Thanks now to
asteroseismology, which can reveal the internal structure of stars,
it becomes possible to compare the predictions from stellar evolution
theory to actual stellar structures. In this work, we present an inverse
analysis of the oscillation data from the solar-type star KIC 6225718,
which was observed by the Kepler space observatory during its nominal
mission. As its mass is about 20% greater than solar, this star is
predicted to transport energy by convection in its nuclear-burning
core. We find significant differences between the predicted and actual
structure of the star in the radiative interior near to the convective
core. In particular, the predicted sound speed is higher than observed
in the deep interior of the star, and too low at a fractional radius
of 0.25 and beyond. The cause of these discrepancies is unknown, and
is not remedied by known physics in the form of convective overshooting
or elemental diffusion.
---------------------------------------------------------
Title: Analytical modelling of period spacings across the HR diagram
Authors: Cunha, M. S.; Avelino, P. P.; Christensen-Dalsgaard, J.;
Stello, D.; Vrard, M.; Jiang, C.; Mosser, B.
2019MNRAS.490..909C Altcode: 2019MNRAS.tmp.2220C; 2019arXiv190904966C
The characterization of stellar cores may be accomplished through
the modelling of asteroseismic data from stars exhibiting either
gravity-mode or mixed-mode pulsations, potentially shedding light on
the physical processes responsible for the production, mixing, and
segregation of chemical elements. In this work, we validate against
model data an analytical expression for the period spacing that will
facilitate the inference of the properties of stellar cores, including
the detection and characterization of buoyancy glitches (strong chemical
gradients). This asymptotically based analytical expression is tested
both in models with and without buoyancy glitches. It does not assume
that glitches are small and, consequently, predicts non-sinusoidal
glitch-induced period-spacing variations, as often seen in model and
real data. We show that the glitch position and width inferred from
the fitting of the analytical expression to model data consisting of
pure gravity modes are in close agreement (typically better than 7
per cent relative difference) with the properties measured directly
from the stellar models. In the case of fitting mixed-mode model data,
the same expression is shown to reproduce well the numerical results,
when the glitch properties are known a priori. In addition, the fits
performed to mixed-mode model data reveal a frequency dependence of the
coupling coefficient, q, for a moderate-luminosity red-giant-branch
model star. Finally, we find that fitting the analytical expression
to the mixed-mode period spacings may provide a way to infer the
frequencies of the pure acoustic dipole modes that would exist if no
coupling took place between acoustic and gravity waves.
---------------------------------------------------------
Title: TESS Asteroseismology of the Known Red-giant Host Stars HD
212771 and HD 203949
Authors: Campante, Tiago L.; Corsaro, Enrico; Lund, Mikkel N.; Mosser,
Benoît; Serenelli, Aldo; Veras, Dimitri; Adibekyan, Vardan; Antia,
H. M.; Ball, Warrick; Basu, Sarbani; Bedding, Timothy R.; Bossini,
Diego; Davies, Guy R.; Delgado Mena, Elisa; García, Rafael A.;
Handberg, Rasmus; Hon, Marc; Kane, Stephen R.; Kawaler, Steven
D.; Kuszlewicz, James S.; Lucas, Miles; Mathur, Savita; Nardetto,
Nicolas; Nielsen, Martin B.; Pinsonneault, Marc H.; Reffert, Sabine;
Silva Aguirre, Víctor; Stassun, Keivan G.; Stello, Dennis; Stock,
Stephan; Vrard, Mathieu; Yıldız, Mutlu; Chaplin, William J.; Huber,
Daniel; Bean, Jacob L.; Çelik Orhan, Zeynep; Cunha, Margarida S.;
Christensen-Dalsgaard, Jørgen; Kjeldsen, Hans; Metcalfe, Travis S.;
Miglio, Andrea; Monteiro, Mário J. P. F. G.; Nsamba, Benard; Örtel,
Sibel; Pereira, Filipe; Sousa, Sérgio G.; Tsantaki, Maria; Turnbull,
Margaret C.
2019ApJ...885...31C Altcode: 2019arXiv190905961C
The Transiting Exoplanet Survey Satellite (TESS) is performing a near
all-sky survey for planets that transit bright stars. In addition, its
excellent photometric precision enables asteroseismology of solar-type
and red-giant stars, which exhibit convection-driven, solar-like
oscillations. Simulations predict that TESS will detect solar-like
oscillations in nearly 100 stars already known to host planets. In this
paper, we present an asteroseismic analysis of the known red-giant host
stars HD 212771 and HD 203949, both systems having a long-period planet
detected through radial velocities. These are the first detections of
oscillations in previously known exoplanet-host stars by TESS, further
showcasing the mission’s potential to conduct asteroseismology of
red-giant stars. We estimate the fundamental properties of both stars
through a grid-based modeling approach that uses global asteroseismic
parameters as input. We discuss the evolutionary state of HD 203949 in
depth and note the large discrepancy between its asteroseismic mass
(M <SUB>*</SUB> = 1.23 ± 0.15 M <SUB>⊙</SUB> if on the red-giant
branch or M <SUB>*</SUB> = 1.00 ± 0.16 M <SUB>⊙</SUB> if in the
clump) and the mass quoted in the discovery paper (M <SUB>*</SUB>
= 2.1 ± 0.1 M <SUB>⊙</SUB>), implying a change >30% in the
planet’s mass. Assuming HD 203949 to be in the clump, we investigate
the planet’s past orbital evolution and discuss how it could have
avoided engulfment at the tip of the red-giant branch. Finally, HD
212771 was observed by K2 during its Campaign 3, thus allowing for
a preliminary comparison of the asteroseismic performances of TESS
and K2. We estimate the ratio of the observed oscillation amplitudes
for this star to be {A}<SUB>\max </SUB><SUP>{TESS</SUP>}/{A}<SUB>\max
</SUB><SUP>K2</SUP>=0.75+/- 0.14, consistent with the expected ratio
of ∼0.85 due to the redder bandpass of TESS.
---------------------------------------------------------
Title: VizieR Online Data Catalog: High-precision radial velocities
for HD 221416 (Huber+, 2019)
Authors: Huber, D.; Chaplin, W. J.; Chontos, A.; Kjeldsen, H.;
Christensen-Dalsgaard, J.; Bedding, T. R.; Ball, W.; Brahm, R.;
Espinoza, N.; Henning, T.; Jordan, A.; Sarkis, P.; Knudstrup, E.;
Albrecht, S.; Grundahl, F.; Andersen, M. F.; Palle, P. L.; Crossfield,
I.; Fulton, B.; Howard, A. W.; Isaacson, H. T.; Weiss, L. M.; Handberg,
R.; Lund, M. N.; Serenelli, A. M.; Rorsted Mosumgaard, J.; Stokholm,
A.; Bieryla, A.; Buchhave, L. A.; Latham, D. W.; Quinn, S. N.;
Gaidos, E.; Hirano, T.; Ricker, G. R.; Vanderspek, R. K.; Seager,
S.; Jenkins, J. M.; Winn, J. N.; Antia, H. M.; Appourchaux, T.; Basu,
S.; Bell, K. J.; Benomar, O.; Bonanno, A.; Buzasi, D. L.; Campante,
T. L.; Celik Orhan, Z.; Corsaro, E.; Cunha, M. S.; Davies, G. R.;
Deheuvels, S.; Grunblatt, S. K.; Hasanzadeh, A.; di Mauro, M. P.;
Garcia, R. A.; Gaulme, P.; Girardi, L.; Guzik, J. A.; Hon, M.; Jiang,
C.; Kallinger, T.; Kawaler, S. D.; Kuszlewicz, J. S.; Lebreton, Y.; Li,
T.; Lucas, M.; Lundkvist, M. S.; Mann, A. W.; Mathis, S.; Mathur, S.;
Mazumdar, A.; Metcalfe, T. S.; Miglio, A.; Monteiro, M. J. P. F. G.;
Mosser, B.; Noll, A.; Nsamba, B.; Ong, J. M. J.; Ortel, S.; Pereira,
F.; Ranadive, P.; Regulo, C.; Rodrigues, T. S.; Roxburgh, I. W.;
Aguirre, V. S.; Smalley, B.; Schofield, M.; Sousa, S. G.; Stassun,
K. G.; Stello, D.; Tayar, J.; White, T. R.; Verma, K.; Vrard, M.;
Yildiz, M.; Baker, D.; Bazot, M.; Beichmann, C.; Bergmann, C.;
Bugnet, L.; Cale, B.; Carlino, R.; Cartwright, S. M.; Christiansen,
J. L.; Ciardi, D. R.; Creevey, O.; Dittmann, J. A.; Do Nascimento,
J. -D., Jr.; van Eylen, V.; Furesz, G.; Gagne, J.; Gao, P.; Gazeas,
K.; Giddens, F.; Hall, O. J.; Hekker, S.; Ireland, M. J.; Latouf,
N.; Lebrun, D.; Levine, A. M.; Matzko, W.; Natinsky, E.; Page, E.;
Plavchan, P.; Mansouri-Samani, M.; McCauliff, S.; Mullally, S. E.;
Orenstein, B.; Soto, A. G.; Paegert, M.; van Saders, J. L.; Schnaible,
C.; Soderblom, D. R.; Szabo, R.; Tanner, A.; Tinney, C. G.; Teske,
J.; Thomas, A.; Trampedach, R.; Wright, D.; Yuan, T. T.; Zohrabi, F.
2019yCat..51570245H Altcode:
We obtained high-resolution spectra of HD 221416 using several
facilities within the TESS Follow-up Observation Program (TFOP),
including HIRES (Vogt et al. 1994SPIE.2198..362V) on the 10 m telescope
at Keck Observatory (Maunakea, Hawai'i); the Hertzsprung SONG Telescope
at Teide Observatory (Tenerife; Grundahl et al. 2017ApJ...836..142G);
HARPS (Mayor et al. 2003Msngr.114...20M), FEROS (Kaufer et
al. 1999Msngr..95....8K), Coralie (Queloz et al. 2001Msngr.105....1Q),
and FIDEOS (Vanzi et al. 2018MNRAS.477.5041V) on the MPG/ESO 3.6 m, 2.2
m, 1.2 m, and 1 m telescopes at La Silla Observatory (Chile); Veloce
(Gilbert et al. 2018SPIE10702E..0YG) on the 3.9 m Anglo-Australian
Telescope at Siding Spring Observatory (Australia); TRES (Furesz 2008,
PhD thesis Univ. Szeged) on the 1.5 m Tillinghast reflector at the
F. L. Whipple Observatory (Mt. Hopkins, Arizona); and iSHELL (Rayner
et al. 2012SPIE.8446E..2CR) on the NASA IRTF Telescope (Maunakea,
Hawai'i). All spectra used in this paper were obtained between 2018
November 11 and December 30 and have a minimum spectral resolution of
R~44000. <P />(1 data file).
---------------------------------------------------------
Title: Solar Models with Convective Overshoot, Solar-wind Mass Loss,
and PMS Disk Accretion: Helioseismic Quantities, Li Depletion,
and Neutrino Fluxes
Authors: Zhang, Qian-Sheng; Li, Yan; Christensen-Dalsgaard, Jørgen
2019ApJ...881..103Z Altcode: 2019arXiv190702166Z
Helioseismic observations have revealed many properties of the Sun:
the depth and helium abundance of the convection zone, the sound speed,
and the density profiles in the solar interior. Those constraints have
been used to judge the stellar evolution theory. With the old solar
composition (e.g., GS98), the solar standard model is in reasonable
agreement with the helioseismic constraints. However, a solar model
with a revised composition (e.g., AGSS09) with a low abundance Z of
heavy elements cannot be consistent with those constraints. This is the
so-called “solar abundance problem,” standing for more than 10 yr
even with the recent upward revised Ne abundance. Many mechanisms have
been proposed to mitigate the problem. However, there is still no low-Z
solar model satisfying all helioseismic constraints. In this paper,
we report a possible solution to the solar abundance problem. With some
extra physical processes that are not included in the standard model,
solar models can be significantly improved. Our new solar models with
convective overshoot, the solar wind, and early mass accretion show
consistency with helioseismic constraints, the solar Li abundance,
and observations of solar neutrino fluxes.
---------------------------------------------------------
Title: Damping rates and frequency corrections of Kepler LEGACY stars
Authors: Houdek, G.; Lund, M. N.; Trampedach, R.;
Christensen-Dalsgaard, J.; Handberg, R.; Appourchaux, T.
2019MNRAS.487..595H Altcode: 2019MNRAS.tmp.1157H; 2019arXiv190413170H
Linear damping rates and modal frequency corrections of radial
oscillation modes in selected LEGACY main-sequence stars are
estimated by means of a non-adiabatic stability analysis. The
selected stellar sample covers stars observed by Kepler with a large
range of surface temperatures and surface gravities. A non-local,
time-dependent convection model is perturbed to assess stability
against pulsation modes. The mixing-length parameter is calibrated
to the surface-convection-zone depth of a stellar model obtained from
fitting adiabatic frequencies to the LEGACY observations, and two of
the non-local convection parameters are calibrated to the corresponding
LEGACY linewidth measurements. The remaining non-local convection
parameters in the 1D calculations are calibrated so as to reproduce
profiles of turbulent pressure and of the anisotropy of the turbulent
velocity field of corresponding 3D hydrodynamical simulations. The
atmospheric structure in the 1D stability analysis adopts a
temperature-optical-depth relation derived from 3D hydrodynamical
simulations. Despite the small number of parameters to adjust, we
find good agreement with detailed shapes of both turbulent pressure
profiles and anisotropy profiles with depth, and with damping rates
as a function of frequency. Furthermore, we find the absolute modal
frequency corrections, relative to a standard adiabatic pulsation
calculation, to increase with surface temperature and surface gravity.
---------------------------------------------------------
Title: A Hot Saturn Orbiting an Oscillating Late Subgiant Discovered
by TESS
Authors: Huber, Daniel; Chaplin, William J.; Chontos, Ashley; Kjeldsen,
Hans; Christensen-Dalsgaard, Jørgen; Bedding, Timothy R.; Ball,
Warrick; Brahm, Rafael; Espinoza, Nestor; Henning, Thomas; Jordán,
Andrés; Sarkis, Paula; Knudstrup, Emil; Albrecht, Simon; Grundahl,
Frank; Fredslund Andersen, Mads; Pallé, Pere L.; Crossfield, Ian;
Fulton, Benjamin; Howard, Andrew W.; Isaacson, Howard T.; Weiss,
Lauren M.; Handberg, Rasmus; Lund, Mikkel N.; Serenelli, Aldo M.;
Rørsted Mosumgaard, Jakob; Stokholm, Amalie; Bieryla, Allyson;
Buchhave, Lars A.; Latham, David W.; Quinn, Samuel N.; Gaidos, Eric;
Hirano, Teruyuki; Ricker, George R.; Vanderspek, Roland K.; Seager,
Sara; Jenkins, Jon M.; Winn, Joshua N.; Antia, H. M.; Appourchaux,
Thierry; Basu, Sarbani; Bell, Keaton J.; Benomar, Othman; Bonanno,
Alfio; Buzasi, Derek L.; Campante, Tiago L.; Çelik Orhan, Z.; Corsaro,
Enrico; Cunha, Margarida S.; Davies, Guy R.; Deheuvels, Sebastien;
Grunblatt, Samuel K.; Hasanzadeh, Amir; Di Mauro, Maria Pia; García,
Rafael A.; Gaulme, Patrick; Girardi, Léo; Guzik, Joyce A.; Hon, Marc;
Jiang, Chen; Kallinger, Thomas; Kawaler, Steven D.; Kuszlewicz, James
S.; Lebreton, Yveline; Li, Tanda; Lucas, Miles; Lundkvist, Mia S.;
Mann, Andrew W.; Mathis, Stéphane; Mathur, Savita; Mazumdar, Anwesh;
Metcalfe, Travis S.; Miglio, Andrea; Monteiro, Mário J. P. F. G.;
Mosser, Benoit; Noll, Anthony; Nsamba, Benard; Ong, Jia Mian Joel;
Örtel, S.; Pereira, Filipe; Ranadive, Pritesh; Régulo, Clara;
Rodrigues, Thaíse S.; Roxburgh, Ian W.; Silva Aguirre, Victor;
Smalley, Barry; Schofield, Mathew; Sousa, Sérgio G.; Stassun,
Keivan G.; Stello, Dennis; Tayar, Jamie; White, Timothy R.; Verma,
Kuldeep; Vrard, Mathieu; Yıldız, M.; Baker, David; Bazot, Michaël;
Beichmann, Charles; Bergmann, Christoph; Bugnet, Lisa; Cale, Bryson;
Carlino, Roberto; Cartwright, Scott M.; Christiansen, Jessie L.;
Ciardi, David R.; Creevey, Orlagh; Dittmann, Jason A.; Do Nascimento,
Jose-Dias, Jr.; Van Eylen, Vincent; Fürész, Gabor; Gagné, Jonathan;
Gao, Peter; Gazeas, Kosmas; Giddens, Frank; Hall, Oliver J.; Hekker,
Saskia; Ireland, Michael J.; Latouf, Natasha; LeBrun, Danny; Levine,
Alan M.; Matzko, William; Natinsky, Eva; Page, Emma; Plavchan,
Peter; Mansouri-Samani, Masoud; McCauliff, Sean; Mullally, Susan E.;
Orenstein, Brendan; Garcia Soto, Aylin; Paegert, Martin; van Saders,
Jennifer L.; Schnaible, Chloe; Soderblom, David R.; Szabó, Róbert;
Tanner, Angelle; Tinney, C. G.; Teske, Johanna; Thomas, Alexandra;
Trampedach, Regner; Wright, Duncan; Yuan, Thomas T.; Zohrabi, Farzaneh
2019AJ....157..245H Altcode: 2019arXiv190101643H
We present the discovery of HD 221416 b, the first transiting planet
identified by the Transiting Exoplanet Survey Satellite (TESS) for
which asteroseismology of the host star is possible. HD 221416 b
(HIP 116158, TOI-197) is a bright (V = 8.2 mag), spectroscopically
classified subgiant that oscillates with an average frequency of
about 430 μHz and displays a clear signature of mixed modes. The
oscillation amplitude confirms that the redder TESS bandpass compared
to Kepler has a small effect on the oscillations, supporting the
expected yield of thousands of solar-like oscillators with TESS 2
minute cadence observations. Asteroseismic modeling yields a robust
determination of the host star radius (R <SUB>⋆</SUB> = 2.943 ±
0.064 R <SUB>⊙</SUB>), mass (M <SUB>⋆</SUB> = 1.212 ± 0.074 M
<SUB>⊙</SUB>), and age (4.9 ± 1.1 Gyr), and demonstrates that it has
just started ascending the red-giant branch. Combining asteroseismology
with transit modeling and radial-velocity observations, we show that
the planet is a “hot Saturn” (R <SUB>p</SUB> = 9.17 ± 0.33 R
<SUB>⊕</SUB>) with an orbital period of ∼14.3 days, irradiance
of F = 343 ± 24 F <SUB>⊕</SUB>, and moderate mass (M <SUB>p</SUB>
= 60.5 ± 5.7 M <SUB>⊕</SUB>) and density (ρ <SUB>p</SUB> = 0.431
± 0.062 g cm<SUP>-3</SUP>). The properties of HD 221416 b show that
the host-star metallicity-planet mass correlation found in sub-Saturns
(4-8 R <SUB>⊕</SUB>) does not extend to larger radii, indicating that
planets in the transition between sub-Saturns and Jupiters follow a
relatively narrow range of densities. With a density measured to ∼15%,
HD 221416 b is one of the best characterized Saturn-size planets to
date, augmenting the small number of known transiting planets around
evolved stars and demonstrating the power of TESS to characterize
exoplanets and their host stars using asteroseismology.
---------------------------------------------------------
Title: Helioseismology and solar neutrinos
Authors: Christensen-Dalsgaard, JøRgen
2019sone.conf...81C Altcode: 2018arXiv180903000C
The studies of solar neutrinos and helioseismology have been closely
intertwined since the first neutrino experiment and the first
observations of solar oscillations in the sixties. Early detailed
helioseismic analyses provided strong support for the standard
solar model and hence a clear indication that the solution to the
discrepancy between the predicted and observed neutrino fluxes had
to be found in terms of neutrino physics, as now fully confirmed
by direct observations. With the full characterization of neutrino
properties we are now in a position to combine neutrino observations and
helioseismology to obtain a more complete understanding of conditions
in the solar core. Here I provide a personal and largely historical
overview of these developments.
---------------------------------------------------------
Title: Stellar modeling and asteroseismology
Authors: Christensen-Dalsgaard, Jorgen
2019psce.confE...3C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Oscillations in the Sun with SONG: Setting the scale for
asteroseismic investigations
Authors: Fredslund Andersen, M.; Pallé, P.; Jessen-Hansen, J.; Wang,
K.; Grundahl, F.; Bedding, T. R.; Roca Cortes, T.; Yu, J.; Mathur,
S.; Gacia, R. A.; Arentoft, T.; Régulo, C.; Tronsgaard, R.; Kjeldsen,
H.; Christensen-Dalsgaard, J.
2019A&A...623L...9F Altcode: 2019arXiv190210717F
Context. We present the first high-cadence multiwavelength
radial-velocity observations of the Sun-as-a-star, carried out during
57 consecutive days using the stellar échelle spectrograph at the
Hertzsprung SONG Telescope operating at the Teide Observatory. <BR />
Aims: Our aim was to produce a high-quality data set and reference
values for the global helioseismic parameters ν<SUB>max, ⊙</SUB> and
Δν<SUB>⊙</SUB> of the solar p-modes using the SONG instrument. The
obtained data set or the inferred values should then be used when
the scaling relations are applied to other stars showing solar-like
oscillations observed with SONG or similar instruments. <BR /> Methods:
We used different approaches to analyse the power spectrum of the time
series to determine ν<SUB>max, ⊙</SUB>: simple Gaussian fitting and
heavy smoothing of the power spectrum. We determined Δν<SUB>⊙</SUB>
using the method of autocorrelation of the power spectrum. The amplitude
per radial mode was determined using the method described in Kjeldsen
et al. (2008, ApJ, 682, 1370). <BR /> Results: We found the following
values for the solar oscillations using the SONG spectrograph:
ν<SUB>max, ⊙</SUB> = 3141 ± 12 μHz, Δν<SUB>⊙</SUB> = 134.98
± 0.04 μHz, and an average amplitude of the strongest radial modes of
16.6 ± 0.4 cm s<SUP>-1</SUP>. These values are consistent with previous
measurements with other techniques. <P />Based on observations made at
the Hertzsprung SONG telescope operated at the Spanish Observatorio
del Teide on the island of Tenerife by the Aarhus and Copenhagen
Universities and by the Instituto de Astrofísica de Canarias.
---------------------------------------------------------
Title: Latitudinal differential rotation in the solar analogues 16
Cygni A and B
Authors: Bazot, M.; Benomar, O.; Christensen-Dalsgaard, J.; Gizon,
L.; Hanasoge, S.; Nielsen, M.; Petit, P.; Sreenivasan, K. R.
2019A&A...623A.125B Altcode: 2019arXiv190201676B
Context. Asteroseismology has undergone a profound transformation
as a scientific field following the CoRoT and Kepler space
missions. The latter is now yielding the first measurements of
latitudinal differential rotation obtained directly from oscillation
frequencies. Differential rotation is a fundamental mechanism of the
stellar dynamo effect. <BR /> Aims: Our goal is to measure the amount
of differential rotation in the solar analogues 16 Cyg A and B, which
are the components of a binary system. These stars are the brightest
observed by Kepler and have therefore been extensively observed, with
exquisite precision on their oscillation frequencies. <BR /> Methods:
We modelled the acoustic power spectrum of 16 Cyg A and B using a model
that takes into account the contribution of differential rotation to
the rotational frequency splitting. The estimation was carried out in a
Bayesian setting. We then inverted these results to obtain the rotation
profile of both stars under the assumption of a solar-like functional
form. <BR /> Results: We observe that the magnitude of latitudinal
differential rotation has a strong chance of being solar-like for
both stars, their rotation rates being higher at the equator than at
the pole. The measured latitudinal differential rotation, defined as
the difference of rotation rate between the equator and the pole, is
320 ± 269 nHz and 440<SUB>-383</SUB><SUP>+363</SUP> nHz for 16 Cyg
A and B, respectively, confirming that the rotation rates of these
stars are almost solar-like. Their equatorial rotation rates are 535
± 75 nHz and 565<SUB>-129</SUB><SUP>+150</SUP> nHz. Our results are
in good agreement with measurements obtained from spectropolarimetry,
spectroscopy, and photometry. <BR /> Conclusions: We present the first
conclusive measurement of latitudinal differential rotation for solar
analogues. Their rotational profiles are very close to those of the
Sun. These results depend weakly on the uncertainties of the stellar
parameters.
---------------------------------------------------------
Title: The Asteroseismic Target List for Solar-like Oscillators
Observed in 2 minute Cadence with the Transiting Exoplanet Survey
Satellite
Authors: Schofield, Mathew; Chaplin, William J.; Huber, Daniel;
Campante, Tiago L.; Davies, Guy R.; Miglio, Andrea; Ball, Warrick
H.; Appourchaux, Thierry; Basu, Sarbani; Bedding, Timothy R.;
Christensen-Dalsgaard, Jørgen; Creevey, Orlagh; García, Rafael A.;
Handberg, Rasmus; Kawaler, Steven D.; Kjeldsen, Hans; Latham, David W.;
Lund, Mikkel N.; Metcalfe, Travis S.; Ricker, George R.; Serenelli,
Aldo; Silva Aguirre, Victor; Stello, Dennis; Vanderspek, Roland
2019ApJS..241...12S Altcode: 2019arXiv190110148S
We present the target list of solar-type stars to be observed in
short-cadence (2 minute) for asteroseismology by the NASA Transiting
Exoplanet Survey Satellite (TESS) during its 2 year nominal survey
mission. The solar-like Asteroseismic Target List (ATL) is comprised
of bright, cool main-sequence and subgiant stars and forms part of the
larger target list of the TESS Asteroseismic Science Consortium. The
ATL uses the Gaia Data Release 2 and the Extended Hipparcos Compilation
(XHIP) to derive fundamental stellar properties, to calculate detection
probabilities, and to produce a rank-ordered target list. We provide a
detailed description of how the ATL was produced and calculate expected
yields for solar-like oscillators based on the nominal photometric
performance by TESS. We also provide a publicly available source code
that can be used to reproduce the ATL, thereby enabling comparisons
of asteroseismic results from TESS with predictions from synthetic
stellar populations.
---------------------------------------------------------
Title: Asteroseismic modelling of the subgiant μ Herculis using SONG
data: lifting the degeneracy between age and model input parameters
Authors: Li, Tanda; Bedding, Timothy R.; Kjeldsen, Hans; Stello,
Dennis; Christensen-Dalsgaard, Jørgen; Deng, Licai
2019MNRAS.483..780L Altcode: 2018arXiv181013015L; 2018MNRAS.tmp.2856L
We model the oscillations of the SONG target μ Herculis to estimate
the parameters of the star. The ℓ = 1 mixed modes of μ Her provide
strong constraints on stellar properties. The mass and age given by our
asteroseismic modelling are 1.10^{+0.11}_{-0.06} M<SUB>⊙</SUB> and
7.55^{+0.96}_{-0.79} Gyr, respectively. The initial helium abundance is
also constrained at around Y<SUB>init</SUB> = 0.28, suggesting a ratio
in the elements enrichment law (ΔY/ΔZ) around 1.3, which is closed
to the solar value. The mixing-length parameter converges to about 1.7,
which is ∼10 per cent lower than the solar value and consistent with
the results from hydrodynamic simulations. Our estimates of stellar
mass and age agree very well with the previous modelling results with
different input physics. Adding asteroseismic information makes these
determinations less model dependent than is typically the case when only
surface information is available. Our studies of the model dependence
(mass, initial helium and metallicity fractions, and the mixing-length
parameter) of the age determination indicate that accurate stellar ages
(≲10 per cent) can be expected from asteroseismic modelling for stars
similar to μ Her. The ℓ = 1 bumped modes, which are sensitive to
the mean density of the helium core, provide a useful `clock' that
provides additional constraints on its age.
---------------------------------------------------------
Title: A giant impact as the likely origin of different twins in
the Kepler-107 exoplanet system
Authors: Bonomo, Aldo S.; Zeng, Li; Damasso, Mario; Leinhardt, Zoë
M.; Justesen, Anders B.; Lopez, Eric; Lund, Mikkel N.; Malavolta,
Luca; Silva Aguirre, Victor; Buchhave, Lars A.; Corsaro, Enrico;
Denman, Thomas; Lopez-Morales, Mercedes; Mills, Sean M.; Mortier,
Annelies; Rice, Ken; Sozzetti, Alessandro; Vanderburg, Andrew;
Affer, Laura; Arentoft, Torben; Benbakoura, Mansour; Bouchy,
François; Christensen-Dalsgaard, Jørgen; Collier Cameron, Andrew;
Cosentino, Rosario; Dressing, Courtney D.; Dumusque, Xavier; Figueira,
Pedro; Fiorenzano, Aldo F. M.; García, Rafael A.; Handberg, Rasmus;
Harutyunyan, Avet; Johnson, John A.; Kjeldsen, Hans; Latham, David W.;
Lovis, Christophe; Lundkvist, Mia S.; Mathur, Savita; Mayor, Michel;
Micela, Giusi; Molinari, Emilio; Motalebi, Fatemeh; Nascimbeni,
Valerio; Nava, Chantanelle; Pepe, Francesco; Phillips, David F.;
Piotto, Giampaolo; Poretti, Ennio; Sasselov, Dimitar; Ségransan,
Damien; Udry, Stéphane; Watson, Chris
2019NatAs...3..416B Altcode: 2019NatAs.tmp..201B; 2019arXiv190201316B
Measures of exoplanet bulk densities indicate that small exoplanets
with radius less than 3 Earth radii (R<SUB>⊕</SUB>) range from
low-density sub-Neptunes containing volatile elements<SUP>1</SUP>
to higher-density rocky planets with Earth-like<SUP>2</SUP> or
iron-rich<SUP>3</SUP> (Mercury-like) compositions. Such astonishing
diversity in observed small exoplanet compositions may be the
product of different initial conditions of the planet-formation
process or different evolutionary paths that altered the planetary
properties after formation<SUP>4</SUP>. Planet evolution may be
especially affected by either photoevaporative mass loss induced by
high stellar X-ray and extreme ultraviolet (XUV) flux<SUP>5</SUP>
or giant impacts<SUP>6</SUP>. Although there is some evidence for
the former<SUP>7,8</SUP>, there are no unambiguous findings so far
about the occurrence of giant impacts in an exoplanet system. Here, we
characterize the two innermost planets of the compact and near-resonant
system Kepler-107 (ref. <SUP>9</SUP>). We show that they have nearly
identical radii (about 1.5-1.6R<SUB>⊕</SUB>), but the outer planet
Kepler-107 c is more than twice as dense (about 12.6 g cm<SUP>-3</SUP>)
as the innermost Kepler-107 b (about 5.3 g cm<SUP>-3</SUP>). In
consequence, Kepler-107 c must have a larger iron core fraction than
Kepler-107 b. This imbalance cannot be explained by the stellar XUV
irradiation, which would conversely make the more-irradiated and
less-massive planet Kepler-107 b denser than Kepler-107 c. Instead,
the dissimilar densities are consistent with a giant impact event
on Kepler-107 c that would have stripped off part of its silicate
mantle. This hypothesis is supported by theoretical predictions from
collisional mantle stripping<SUP>10</SUP>, which match the mass and
radius of Kepler-107 c.
---------------------------------------------------------
Title: TESS Discovery of an Ultra-short-period Planet around the
Nearby M Dwarf LHS 3844
Authors: Vanderspek, Roland; Huang, Chelsea X.; Vanderburg, Andrew;
Ricker, George R.; Latham, David W.; Seager, Sara; Winn, Joshua N.;
Jenkins, Jon M.; Burt, Jennifer; Dittmann, Jason; Newton, Elisabeth;
Quinn, Samuel N.; Shporer, Avi; Charbonneau, David; Irwin, Jonathan;
Ment, Kristo; Winters, Jennifer G.; Collins, Karen A.; Evans, Phil;
Gan, Tianjun; Hart, Rhodes; Jensen, Eric L. N.; Kielkopf, John;
Mao, Shude; Waalkes, William; Bouchy, François; Marmier, Maxime;
Nielsen, Louise D.; Ottoni, Gaël; Pepe, Francesco; Ségransan,
Damien; Udry, Stéphane; Henry, Todd; Paredes, Leonardo A.; James,
Hodari-Sadiki; Hinojosa, Rodrigo H.; Silverstein, Michele L.; Palle,
Enric; Berta-Thompson, Zachory; Crossfield, Ian; Davies, Misty D.;
Dragomir, Diana; Fausnaugh, Michael; Glidden, Ana; Pepper, Joshua;
Morgan, Edward H.; Rose, Mark; Twicken, Joseph D.; Villaseñor, Jesus
Noel S.; Yu, Liang; Bakos, Gaspar; Bean, Jacob; Buchhave, Lars A.;
Christensen-Dalsgaard, Jørgen; Christiansen, Jessie L.; Ciardi,
David R.; Clampin, Mark; De Lee, Nathan; Deming, Drake; Doty, John;
Jernigan, J. Garrett; Kaltenegger, Lisa; Lissauer, Jack J.; McCullough,
P. R.; Narita, Norio; Paegert, Martin; Pal, Andras; Rinehart, Stephen;
Sasselov, Dimitar; Sato, Bun'ei; Sozzetti, Alessandro; Stassun,
Keivan G.; Torres, Guillermo
2019ApJ...871L..24V Altcode: 2018arXiv180907242V
Data from the newly commissioned Transiting Exoplanet Survey Satellite
has revealed a “hot Earth” around LHS 3844, an M dwarf located 15
pc away. The planet has a radius of 1.303+/- 0.022 R <SUB>⊕</SUB> and
orbits the star every 11 hr. Although the existence of an atmosphere
around such a strongly irradiated planet is questionable, the star
is bright enough (I = 11.9, K = 9.1) for this possibility to be
investigated with transit and occultation spectroscopy. The star’s
brightness and the planet’s short period will also facilitate the
measurement of the planet’s mass through Doppler spectroscopy.
---------------------------------------------------------
Title: Asteroseismology of the Hyades red giant and planet host
ɛ Tauri
Authors: Arentoft, T.; Grundahl, F.; White, T. R.; Slumstrup, D.;
Handberg, R.; Lund, M. N.; Brogaard, K.; Andersen, M. F.; Silva
Aguirre, V.; Zhang, C.; Chen, X.; Yan, Z.; Pope, B. J. S.; Huber, D.;
Kjeldsen, H.; Christensen-Dalsgaard, J.; Jessen-Hansen, J.; Antoci,
V.; Frandsen, S.; Bedding, T. R.; Pallé, P. L.; Garcia, R. A.; Deng,
L.; Hon, M.; Stello, D.; Jørgensen, U. G.
2019A&A...622A.190A Altcode: 2019arXiv190106187A
Context. Asteroseismic analysis of solar-like stars allows us to
determine physical parameters such as stellar mass, with a higher
precision compared to most other methods. Even in a well-studied cluster
such as the Hyades, the masses of the red giant stars are not well
known, and previous mass estimates are based on model calculations
(isochrones). The four known red giants in the Hyades are assumed
to be clump (core-helium-burning) stars based on their positions
in colour-magnitude diagrams, however asteroseismology offers an
opportunity to test this assumption. <BR /> Aims: Using asteroseismic
techniques combined with other methods, we aim to derive physical
parameters and the evolutionary stage for the planet hosting star ɛ
Tau, which is one of the four red giants located in the Hyades. <BR />
Methods: We analysed time-series data from both ground and space to
perform the asteroseismic analysis. By combining high signal-to-noise
radial-velocity data from the ground-based SONG network with continuous
space-based data from the revised Kepler mission K2, we derive and
characterize 27 individual oscillation modes for ɛ Tau, along with
global oscillation parameters such as the large frequency separation
Δν and the ratio between the amplitude of the oscillations measured
in radial velocity and intensity as a function of frequency. The
latter has been measured previously for only two stars, the Sun and
Procyon. Combining the seismic analysis with interferometric and
spectroscopic measurements, we derive physical parameters for ɛ
Tau, and discuss its evolutionary status. <BR /> Results: Along with
other physical parameters, we derive an asteroseismic mass for ɛ
Tau of M = 2.458 ± 0.073 M<SUB>⊙</SUB>, which is slightly lower
than previous estimates, and which leads to a revised minimum mass
of the planetary companion. Noting that the SONG and K2 data are
non-simultaneous, we estimate the amplitude ratio between intensity
and radial velocity to be 42.2 ± 2.3 ppm m<SUP>-1</SUP> s, which
is higher than expected from scaling relations. <P />Time-series
data are only available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/622/A190">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/622/A190</A>Based
on observations made with the SONG telescopes operated on the
Spanish Observatorio del Teide (Tenerife) and at the Chinese Delingha
Observatory (Qinghai) by the Aarhus and Copenhagen Universities, by the
Instituto de Astrofísica de Canarias and by the National Astronomical
Observatories of China, and with NASA's K2 mission.
---------------------------------------------------------
Title: VizieR Online Data Catalog: eps Tau intensity and RV
time-series data (Arentoft+, 2019)
Authors: Arentoft, T.; Grundahl, F.; White, T. R.; Slumstrup, D.;
Handberg, R.; Lund, M. N.; Brogaard, K.; Andersen, M. F.; Silva
Aguirre, V.; Zhang, C.; Chen, X.; Yan, Z.; Pope, B. J. S.; Huber, D.;
Kjeldsen, H.; Christensen-Dalsgaard, J.; Jessen-Hansen, J.; Antoci,
V.; Frandsen, S.; Bedding, T. R.; Palle, P. L.; Garcia, R. A.; Deng,
L.; Hon, M.; Stello, D.; Jorgensen, U. G.
2019yCat..36220190A Altcode:
Time-series data for epsilon Tau; photometric time-series data from
the revised Kepler mission K2 and radial-velocity measurements from
SONG (Stellar Observations Network Group). The time series have been
filtered in order to remove variations and instrumental effects at
low frequencies. <P />(2 data files).
---------------------------------------------------------
Title: TESS Discovery of a Transiting Super-Earth in the pi Mensae
System
Authors: Huang, Chelsea X.; Burt, Jennifer; Vanderburg, Andrew;
Günther, Maximilian N.; Shporer, Avi; Dittmann, Jason A.; Winn,
Joshua N.; Wittenmyer, Rob; Sha, Lizhou; Kane, Stephen R.; Ricker,
George R.; Vanderspek, Roland K.; Latham, David W.; Seager, Sara;
Jenkins, Jon M.; Caldwell, Douglas A.; Collins, Karen A.; Guerrero,
Natalia; Smith, Jeffrey C.; Quinn, Samuel N.; Udry, Stéphane; Pepe,
Francesco; Bouchy, François; Ségransan, Damien; Lovis, Christophe;
Ehrenreich, David; Marmier, Maxime; Mayor, Michel; Wohler, Bill;
Haworth, Kari; Morgan, Edward H.; Fausnaugh, Michael; Ciardi,
David R.; Christiansen, Jessie; Charbonneau, David; Dragomir, Diana;
Deming, Drake; Glidden, Ana; Levine, Alan M.; McCullough, P. R.; Yu,
Liang; Narita, Norio; Nguyen, Tam; Morton, Tim; Pepper, Joshua; Pál,
András; Rodriguez, Joseph E.; Stassun, Keivan G.; Torres, Guillermo;
Sozzetti, Alessandro; Doty, John P.; Christensen-Dalsgaard, Jørgen;
Laughlin, Gregory; Clampin, Mark; Bean, Jacob L.; Buchhave, Lars A.;
Bakos, G. Á.; Sato, Bun'ei; Ida, Shigeru; Kaltenegger, Lisa; Palle,
Enric; Sasselov, Dimitar; Butler, R. P.; Lissauer, Jack; Ge, Jian;
Rinehart, S. A.
2018ApJ...868L..39H Altcode: 2018arXiv180905967H
We report the detection of a transiting planet around π Men (HD 39091),
using data from the Transiting Exoplanet Survey Satellite (TESS). The
solar-type host star is unusually bright (V = 5.7) and was already
known to host a Jovian planet on a highly eccentric, 5.7 yr orbit. The
newly discovered planet has a size of 2.04 ± 0.05 R <SUB>⊕</SUB>
and an orbital period of 6.27 days. Radial-velocity data from the
High-Accuracy Radial-velocity Planet Searcher and Anglo-Australian
Telescope/University College London Echelle Spectrograph archives
also displays a 6.27 day periodicity, confirming the existence
of the planet and leading to a mass determination of 4.82 ±
0.85 M <SUB>⊕</SUB>. The star’s proximity and brightness will
facilitate further investigations, such as atmospheric spectroscopy,
asteroseismology, the Rossiter-McLaughlin effect, astrometry, and
direct imaging.
---------------------------------------------------------
Title: Coupling 1D stellar evolution with 3D-hydrodynamical
simulations on the fly - I. A new standard solar model
Authors: Jørgensen, Andreas Christ Sølvsten; Mosumgaard, Jakob
Rørsted; Weiss, Achim; Silva Aguirre, Víctor; Christensen-Dalsgaard,
Jørgen
2018MNRAS.481L..35J Altcode: 2018arXiv180808886C; 2018MNRAS.tmpL.155J
Standard 1D stellar evolution models do not correctly reproduce
the structure of the outermost layers of stars with convective
envelopes. This has been a long-standing problem in stellar modelling
affecting both the predicted evolutionary paths and the attributed
oscillation frequencies, and indirectly biasing numerous quantities
derived from stellar evolution calculations. We present a novel method
that mostly eliminates these structural defects by appending mean 3D
simulations of stellar envelopes. In contrast to previous attempts,
we impose the complete structure derived from 3D simulations at
each time-step during the entire evolution. For this purpose, we
interpolate in grids of pre-computed 3D simulations and use the
resulting structure as boundary conditions, in order to solve the
stellar structure equations for the 1D interior at each time-step. Our
method provides a continuous transition in many quantities from the
interior to the imposed interpolated 3D surface layers. We present
a solar calibration model and show that the obtained structure of the
surface layers reliably mimics that of the underlying 3D simulations for
the present Sun. Moreover, we perform a helioseismic analysis, showing
that our method mostly eliminates the structural contribution to the
discrepancy between model frequencies and observed p-mode frequencies.
---------------------------------------------------------
Title: Modelling the solar twin 18 Scorpii
Authors: Bazot, M.; Creevey, O.; Christensen-Dalsgaard, J.;
Meléndez, J.
2018A&A...619A.172B Altcode: 2018arXiv181001387B
Context. Solar twins are objects of great interest in that they allow us
to understand better how stellar evolution and structure are affected
by variations of the stellar mass, age and chemical composition in
the vicinity of the commonly accepted solar values. <BR /> Aims:
We aim to use the existing spectrophotometric, interferometric and
asteroseismic data for the solar twin 18 Sco to constrain stellar
evolution models. 18 Sco is the brightest solar twin and is a good
benchmark for the study of solar twins. The goal is to obtain
realistic estimates of its physical characteristics (mass, age,
initial chemical composition, mixing-length parameter) and realistic
associated uncertainties using stellar models. <BR /> Methods: We set
up a Bayesian model that relates the statistical properties of the
data to the probability density of the stellar parameters. Special
care is given to the modelling of the likelihood for the seismic
data, using Gaussian mixture models. The probability densities of
the stellar parameters are approximated numerically using an adaptive
MCMC algorithm. From these approximate distributions we proceeded to a
statistical analysis. We also performed the same exercise using local
optimisation. <BR /> Results: The precision on the mass is approximately
6%. The precision reached on X<SUB>0</SUB> and Z<SUB>0</SUB> and
the mixing-length parameter are respectively 6%, 9%, and 35%. The
posterior density for the age is bimodal, with modes at 4.67 Gyr
and 6.95 Gyr, the first one being slightly more likely. We show that
this bimodality is directly related to the structure of the seismic
data. When asteroseismic data or interferometric data are excluded,
we find significant losses of precision for the mass and the initial
hydrogen-mass fraction. Our final estimates of the uncertainties from
the Bayesian analysis are significantly larger than values inferred
from local optimization. This also holds true for several estimates
of the age encountered in the literature. <P />Based on observations
collected at the European Organisation for Astronomical Research in
the Southern Hemisphere, Chile (run ID: 183.D-0729(A)).
---------------------------------------------------------
Title: Butterfly diagram of a Sun-like star observed using
asteroseismology
Authors: Bazot, M.; Nielsen, M. B.; Mary, D.; Christensen-Dalsgaard,
J.; Benomar, O.; Petit, P.; Gizon, L.; Sreenivasan, K. R.; White, T. R.
2018A&A...619L...9B Altcode: 2018arXiv181008630B
Stellar magnetic fields are poorly understood, but are known to be
important for stellar evolution and exoplanet habitability. They
drive stellar activity, which is the main observational
constraint on theoretical models for magnetic field generation and
evolution. Starspots are the main manifestation of the magnetic fields
at the stellar surface. In this study we measured the variation in
their latitude with time, called a butterfly diagram in the solar case,
for the solar analogue HD 173701 (KIC 8006161). To this end, we used
Kepler data to combine starspot rotation rates at different epochs and
the asteroseismically determined latitudinal variation in the stellar
rotation rates. We observe a clear variation in the latitude of the
starspots. It is the first time such a diagram has been constructed
using asteroseismic data.
---------------------------------------------------------
Title: Asteroseismic detection of latitudinal differential rotation
in 13 Sun-like stars
Authors: Benomar, O.; Bazot, M.; Nielsen, M. B.; Gizon, L.; Sekii,
T.; Takata, M.; Hotta, H.; Hanasoge, S.; Sreenivasan, K. R.;
Christensen-Dalsgaard, J.
2018Sci...361.1231B Altcode: 2018arXiv180907938B
The differentially rotating outer layers of stars are thought to
play a role in driving their magnetic activity, but the underlying
mechanisms that generate and sustain differential rotation are
poorly understood. We report the measurement using asteroseismology
of latitudinal differential rotation in the convection zones of 40
Sun-like stars. For the most significant detections, the stars’
equators rotate approximately twice as fast as their midlatitudes. The
latitudinal shear inferred from asteroseismology is much larger than
predictions from numerical simulations.
---------------------------------------------------------
Title: High-precision abundances of elements in stars with
asteroseismic ages
Authors: Nissen, P. E.; Aguirre, V. Silva; Christensen-Dalsgaard,
J.; Collet, R.; Grundahl, F.; Slumstrup, D.
2018IAUS..334..166N Altcode:
High-precision abundances of elements have been derived from HARPS-N
spectra of F and G main-sequence stars having ages determined from
oscillation frequencies delivered by the Kepler mission. The tight
relations between abundance ratios of refractory elements, e.g.,
[Mg/Fe] and [Y/Mg], and stellar age previously found for solar
twin stars are confirmed. These relations provide new information
on nucleosynthesis and Galactic evolution. Abundance ratios between
volatile and refractory elements, e.g., [C/Fe] and [O/Fe], show on the
other hand a significant scatter at a given age, which may be related
to planet-star interactions. This is a potential problem for chemical
tagging studies.
---------------------------------------------------------
Title: Using low-mass stars as a tool: efforts towards precise models
Authors: Weiss, Achim; Aguirre, Victor Silva; Christensen-Dalsgaard,
Jørgen
2018IAUS..334..178W Altcode:
We present results of an on-going effort to identify the minimum level
of systematic, purely numerical differences in low-mass stellar models
on the Red Giant Branch, by comparing models in selected phases for
pre-defined physical input assumptions.
---------------------------------------------------------
Title: Stellar models with calibrated convection and temperature
stratification from 3D hydrodynamics simulations
Authors: Mosumgaard, Jakob Rørsted; Ball, Warrick H.; Silva Aguirre,
Víctor; Weiss, Achim; Christensen-Dalsgaard, Jørgen
2018MNRAS.478.5650M Altcode: 2018arXiv180600020R; 2018MNRAS.tmp.1388M; 2018MNRAS.478.5663M
Stellar evolution codes play a major role in present-day astrophysics,
yet they share common simplifications related to the outer layers
of stars. We seek to improve on this by the use of results from
realistic and highly detailed 3D hydrodynamics simulations of stellar
convection. We implement a temperature stratification extracted directly
from the 3D simulations into two stellar evolution codes to replace the
simplified atmosphere normally used. Our implementation also contains
a non-constant mixing-length parameter, which varies as a function of
the stellar surface gravity and temperature - also derived from the
3D simulations. We give a detailed account of our fully consistent
implementation and compare to earlier works, and also provide a
freely available MESA-module. The evolution of low-mass stars with
different masses is investigated, and we present for the first time an
asteroseismic analysis of a standard solar model utilizing calibrated
convection and temperature stratification from 3D simulations. We show
that the inclusion of 3D results has an almost insignificant impact on
the evolution and structure of stellar models - the largest effect are
changes in effective temperature of order 30 K seen in the pre-main
sequence and in the red-giant branch. However, this work provides the
first step for producing self-consistent evolutionary calculations
using fully incorporated 3D atmospheres from on-the-fly interpolation
in grids of simulations.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Kepler planetary cand. VIII. DR25
reliability (Thompson+, 2018)
Authors: Thompson, S. E.; Coughlin, J. L.; Hoffman, K.; Mullally,
F.; Christiansen, J. L.; Burke, C. J.; Bryson, S.; Batalha, N.; Haas,
M. R.; Catanzarite, J.; Rowe, J. F.; Barentsen, G.; Caldwell, D. A.;
Clarke, B. D.; Jenkins, J. M.; Li, J.; Latham, D. W.; Lissauer, J. J.;
Mathur, S.; Morris, R. L.; Seader, S. E.; Smith, J. C.; Klaus, T. C.;
Twicken, J. D.; van Cleve, J. E.; Wohler, B.; Akeson, R.; Ciardi,
D. R.; Cochran, W. D.; Henze, C. E.; Howell, S. B.; Huber, D.; Prsa,
A.; Ramirez, S. V.; Morton, T. D.; Barclay, T.; Campbell, J. R.;
Chaplin, W. J.; Charbonneau, D.; Christensen-Dalsgaard, J.; Dotson,
J. L.; Doyle, L.; Dunham, E. W.; Dupree, A. K.; Ford, E. B.; Geary,
J. C.; Girouard, F. R.; Isaacson, H.; Kjeldsen, H.; Quintana, E. V.;
Ragozzine, D.; Shabram, M.; Shporer, A.; Aguirre, V. S.; Steffen,
J. H.; Still, M.; Tenenbaum, P.; Welsh, W. F.; Wolfgang, A.; Zamudio,
K. A.; Koch, D. G.; Borucki, W. J.
2018yCat..22350038T Altcode:
We present the Kepler Object of Interest (KOI) catalog of transiting
exoplanets based on searching 4yr of Kepler time series photometry (Data
Release 25, Q1-Q17: Twicken+, 2016, J/AJ/152/158). The catalog contains
8054 KOIs, of which 4034 are planet candidates with periods between
0.25 and 632 days. Of these candidates, 219 are new, including two in
multiplanet systems (KOI-82.06 and KOI-2926.05) and 10 high-reliability,
terrestrial-size, habitable zone candidates. This catalog was created
using a tool called the Robovetter, which automatically vets the DR25
threshold crossing events (TCEs). The Robovetter also vetted simulated
data sets and measured how well it was able to separate TCEs caused by
noise from those caused by low signal-to-noise transits. We discuss
the Robovetter and the metrics it uses to sort TCEs. For orbital
periods less than 100 days the Robovetter completeness (the fraction
of simulated transits that are determined to be planet candidates)
across all observed stars is greater than 85%. For the same period
range, the catalog reliability (the fraction of candidates that are not
due to instrumental or stellar noise) is greater than 98%. However,
for low signal-to-noise candidates between 200 and 500 days around
FGK-dwarf stars, the Robovetter is 76.7% complete and the catalog is
50.5% reliable. <P />(6 data files).
---------------------------------------------------------
Title: On the hydrostatic stratification of the solar tachocline
Authors: Christensen-Dalsgaard, J.; Gough, D. O.; Knudstrup, E.
2018MNRAS.477.3845C Altcode: 2018MNRAS.tmp..730C; 2018arXiv180308675C
We present an attempt to reconcile the solar tachocline glitch, a thin
layer immediately beneath the convection zone in which the seismically
inferred sound speed in the Sun exceeds corresponding values in standard
solar models, with a degree of partial material mixing which we presume
to have resulted from a combination of convective overshoot, wave
transport, and tachocline circulation. We first summarize the effects
either of modifying in the models the opacity in the radiative interior
or of incorporating either slow or fast tachocline circulation. Neither
alone is successful. We then consider, without physical justification,
incomplete material redistribution immediately beneath the convection
zone which is slow enough not to disturb radiative equilibrium. It is
modelled simply as a diffusion process. We find that, in combination
with an appropriate opacity modification, it is possible to find a
density-dependent diffusion coefficient that removes the glitch almost
entirely, with a radiative envelope that is consistent with seismology.
---------------------------------------------------------
Title: Modelling linewidths of Kepler red giants in NGC 6819
Authors: Aarslev, Magnus J.; Houdek, Günter; Handberg, Rasmus;
Christensen-Dalsgaard, Jørgen
2018MNRAS.478...69A Altcode: 2018MNRAS.tmp..945A; 2018arXiv180406255A
We present a comparison between theoretical, frequency-dependent,
damping rates and linewidths of radial-mode oscillations in red giant
stars located in the open cluster NGC 6819. The calculations adopt a
time-dependent non-local convection model, with the turbulent pressure
profile being calibrated to results of 3D hydrodynamical simulations
of stellar atmospheres. The linewidths are obtained from extensive
peakbagging of Kepler light curves. These observational results are
of unprecedented quality owing to the long continuous observations
by Kepler. The uniqueness of the Kepler mission also means that, for
asteroseismic properties, this is the best data that will be available
for a long time to come. We therefore take great care in modelling
nine RGB stars in NGC 6819 using information from 3D simulations to
obtain realistic temperature stratifications and calibrated turbulent
pressure profiles. Our modelled damping rates reproduce well the Kepler
observations, including the characteristic depression in the linewidths
around the frequency of maximum oscillation power. Furthermore, we
thoroughly test the sensitivity of the calculated damping rates to
changes in the parameters of the non-local convection model.
---------------------------------------------------------
Title: The mass and age of the first SONG target: the red giant 46 LMi
Authors: Frandsen, S.; Fredslund Andersen, M.; Brogaard, K.; Jiang,
C.; Arentoft, T.; Grundahl, F.; Kjeldsen, H.; Christensen-Dalsgaard,
J.; Weiss, E.; Pallé, P.; Antoci, V.; Kjærgaard, P.; Sørensen,
A. N.; Skottfelt, J.; Jørgensen, U. G.
2018A&A...613A..53F Altcode: 2018arXiv180602095F
Context. The Stellar Observation Network Group (SONG) is an initiative
to build a worldwide network of 1m telescopes with high-precision
radial-velocity spectrographs. Here we analyse the first radial-velocity
time series of a red-giant star measured by the SONG telescope at
Tenerife. The asteroseismic results demonstrate a major increase
in the achievable precision of the parameters for red-giant stars
obtainable from ground-based observations. Reliable tests of the
validity of these results are needed, however, before the accuracy of
the parameters can be trusted. <BR /> Aims: We analyse the first SONG
time series for the star 46 LMi, which has a precise parallax and an
angular diameter measured from interferometry, and therefore a good
determination of the stellar radius. We use asteroseismic scaling
relations to obtain an accurate mass, and modelling to determine the
age. <BR /> Methods: A 55-day time series of high-resolution, high S/N
spectra were obtained with the first SONG telescope. We derive the
asteroseismic parameters by analysing the power spectrum. To give a
best guess on the large separation of modes in the power spectrum, we
have applied a new method which uses the scaling of Kepler red-giant
stars to 46 LMi. <BR /> Results: Several methods have been applied:
classical estimates, seismic methods using the observed time series,
and model calculations to derive the fundamental parameters of 46
LMi. Parameters determined using the different methods are consistent
within the uncertainties. We find the following values for the mass M
(scaling), radius R (classical), age (modelling), and surface gravity
(combining mass and radius): M = 1.09 ± 0.04M<SUB>⊙</SUB>,
R = 7.95 ± 0.11R<SUB>⊙</SUB> age t = 8.2 ± 1.9 Gy, and logg =
2.674 ± 0.013. <BR /> Conclusions: The exciting possibilities for
ground-based asteroseismology of solar-like oscillations with a fully
robotic network have been illustrated with the results obtained from
just a single site of the SONG network. The window function is still
a severe problem which will be solved when there are more nodes in
the network. <P />Based on observations made with the Hertzsprung
SONG telescope operated at the Spanish Observatorio del Teide on the
island of Tenerife by the Aarhus and Copenhagen Universities and by
the Instituto de Astrofísica de Canarias.
---------------------------------------------------------
Title: Asteroseismology with solar-like oscillations
Authors: Christensen-Dalsgaard, Jørgen
2018vsss.book..125C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Planetary Candidates Observed by Kepler. VIII. A Fully
Automated Catalog with Measured Completeness and Reliability Based
on Data Release 25
Authors: Thompson, Susan E.; Coughlin, Jeffrey L.; Hoffman, Kelsey;
Mullally, Fergal; Christiansen, Jessie L.; Burke, Christopher J.;
Bryson, Steve; Batalha, Natalie; Haas, Michael R.; Catanzarite,
Joseph; Rowe, Jason F.; Barentsen, Geert; Caldwell, Douglas A.;
Clarke, Bruce D.; Jenkins, Jon M.; Li, Jie; Latham, David W.; Lissauer,
Jack J.; Mathur, Savita; Morris, Robert L.; Seader, Shawn E.; Smith,
Jeffrey C.; Klaus, Todd C.; Twicken, Joseph D.; Van Cleve, Jeffrey
E.; Wohler, Bill; Akeson, Rachel; Ciardi, David R.; Cochran, William
D.; Henze, Christopher E.; Howell, Steve B.; Huber, Daniel; Prša,
Andrej; Ramírez, Solange V.; Morton, Timothy D.; Barclay, Thomas;
Campbell, Jennifer R.; Chaplin, William J.; Charbonneau, David;
Christensen-Dalsgaard, Jørgen; Dotson, Jessie L.; Doyle, Laurance;
Dunham, Edward W.; Dupree, Andrea K.; Ford, Eric B.; Geary, John C.;
Girouard, Forrest R.; Isaacson, Howard; Kjeldsen, Hans; Quintana, Elisa
V.; Ragozzine, Darin; Shabram, Megan; Shporer, Avi; Silva Aguirre,
Victor; Steffen, Jason H.; Still, Martin; Tenenbaum, Peter; Welsh,
William F.; Wolfgang, Angie; Zamudio, Khadeejah A.; Koch, David G.;
Borucki, William J.
2018ApJS..235...38T Altcode: 2017arXiv171006758T
We present the Kepler Object of Interest (KOI) catalog of transiting
exoplanets based on searching 4 yr of Kepler time series photometry
(Data Release 25, Q1-Q17). The catalog contains 8054 KOIs, of which
4034 are planet candidates with periods between 0.25 and 632 days. Of
these candidates, 219 are new, including two in multiplanet systems
(KOI-82.06 and KOI-2926.05) and 10 high-reliability, terrestrial-size,
habitable zone candidates. This catalog was created using a tool called
the Robovetter, which automatically vets the DR25 threshold crossing
events (TCEs). The Robovetter also vetted simulated data sets and
measured how well it was able to separate TCEs caused by noise from
those caused by low signal-to-noise transits. We discuss the Robovetter
and the metrics it uses to sort TCEs. For orbital periods less than 100
days the Robovetter completeness (the fraction of simulated transits
that are determined to be planet candidates) across all observed stars
is greater than 85%. For the same period range, the catalog reliability
(the fraction of candidates that are not due to instrumental or stellar
noise) is greater than 98%. However, for low signal-to-noise candidates
between 200 and 500 days around FGK-dwarf stars, the Robovetter is
76.7% complete and the catalog is 50.5% reliable. The KOI catalog,
the transit fits, and all of the simulated data used to characterize
this catalog are available at the NASA Exoplanet Archive.
---------------------------------------------------------
Title: Using the phase shift to asymptotically characterize the
dipolar mixed modes in post-main-sequence stars
Authors: Jiang, C.; Christensen-Dalsgaard, J.; Cunha, M.
2018MNRAS.474.5413J Altcode: 2017arXiv171202966J
Mixed modes have been extensively observed in post-main-sequence
stars by the Kepler and CoRoT space missions. The mixture of the
p and g modes can be measured by the dimensionless coefficient q,
the so-called coupling strength factor. In this paper, we discuss
the utility of the phase shifts θ from the eigenvalue condition
for mixed modes as a tool to characterize dipolar mixed modes from
the theoretical as well as the practical point of view. Unlike the
coupling strength, whose variation in a given star is very small over
the relevant frequency range, the phase shifts vary significantly
for different modes. The analysis in terms of θ can also provide a
better understanding of the pressure and gravity radial order for a
given mixed mode. Observed frequencies of the Kepler red-giant star
KIC 3744043 are used to test the method. The results are very promising.
---------------------------------------------------------
Title: Helioseismology: Observations and Space Missions
Authors: Palle, P. L.; Appourchaux, T.; Christensen-Dalsgaard, J.;
Garcia, R. A.
2018arXiv180200674P Altcode:
The great success of Helioseismology resides in the remarkable
progress achieved in the understanding of the structure and dynamics
of the solar interior. This success mainly relies on the ability to
conceive, implement, and operate specific instrumentation with enough
sensitivity to detect and measure small fluctuations (in velocity
and/or intensity) on the solar surface that are well below one meter
per second or a few parts per million. Furthermore the limitation of
the ground observations imposing the day-night cycle (thus a periodic
discontinuity in the observations) was overcome with the deployment of
ground-based networks --properly placed at different longitudes all
over the Earth-- allowing longer and continuous observations of the
Sun and consequently increasing their duty cycles. In this chapter,
we start by a short historical overview of helioseismology. Then we
describe the different techniques used to do helioseismic analyses along
with a description of the main instrumental concepts. We in particular
focus on the instruments that have been operating long enough to study
the solar magnetic activity. Finally, we give a highlight of the main
results obtained with such high-duty cycle observations (>80%)
lasting over the last few decades.
---------------------------------------------------------
Title: Ages for Exoplanet Host Stars
Authors: Christensen-Dalsgaard, Jørgen; Aguirre, Víctor Silva
2018haex.bookE.184C Altcode: 2018arXiv180303125C
Age is an important characteristic of a planetary system but also one
that is difficult to determine. Assuming that the host star and the
planets are formed at the same time, the challenge is to determine
the stellar age. Asteroseismology provides precise age determination,
but in many cases the required detailed pulsation observations are
not available. Here we concentrate on other techniques, which may
have broader applicability but also serious limitations. Further
development of this area requires improvements in our understanding
of the evolution of stars and their age-dependent characteristics,
combined with observations that allow reliable calibration of the
various techniques.
---------------------------------------------------------
Title: High-precision abundances of elements in Kepler LEGACY
stars. Verification of trends with stellar age
Authors: Nissen, P. E.; Silva Aguirre, V.; Christensen-Dalsgaard,
J.; Collet, R.; Grundahl, F.; Slumstrup, D.
2017A&A...608A.112N Altcode: 2017arXiv171003544N
Context. A previous study of solar twin stars has revealed the existence
of correlations between some abundance ratios and stellar age providing
new knowledge about nucleosynthesis and Galactic chemical evolution. <BR
/> Aims: High-precision abundances of elements are determined for stars
with asteroseismic ages in order to test the solar twin relations. <BR
/> Methods: HARPS-N spectra with signal-to-noise ratios S/N ≳ 250
and MARCS model atmospheres were used to derive abundances of C, O, Na,
Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Zn, and Y in ten stars from the Kepler
LEGACY sample (including the binary pair 16 Cyg A and B) selected to
have metallicities in the range - 0.15 < [ Fe / H ] < + 0.15 and
ages between 1 and 7 Gyr. Stellar gravities were obtained from seismic
data and effective temperatures were determined by comparing non-LTE
iron abundances derived from Fe I and Fe II lines. Available non-LTE
corrections were also applied when deriving abundances of the other
elements. <BR /> Results: The abundances of the Kepler stars support
the [X/Fe]-age relations previously found for solar twins. [Mg/Fe],
[Al/Fe], and [Zn/Fe] decrease by 0.1 dex over the lifetime of the
Galactic thin disk due to delayed contribution of iron from Type
Ia supernovae relative to prompt production of Mg, Al, and Zn in
Type II supernovae. [Y/Mg] and [Y/Al], on the other hand, increase
by 0.3 dex, which can be explained by an increasing contribution
of s-process elements from low-mass AGB stars as time goes on. The
trends of [C/Fe] and [O/Fe] are more complicated due to variations
of the ratio between refractory and volatile elements among stars of
similar age. Two stars with about the same age as the Sun show very
different trends of [X/H] as a function of elemental condensation
temperature T<SUB>c</SUB> and for 16 Cyg, the two components have
an abundance difference, which increases with T<SUB>c</SUB>. These
anomalies may be connected to planet-star interactions. <P />Based on
spectra obtained with HARPS-N@TNG under programme A33TAC_1.Tables
1 and 2 are also available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
(<A href="http://130.79.128.5">http://130.79.128.5</A>) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/608/A112">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/608/A112</A>
---------------------------------------------------------
Title: Asteroseismic masses of retired planet-hosting A-stars
using SONG
Authors: Stello, Dennis; Huber, Daniel; Grundahl, Frank; Lloyd,
James; Ireland, Mike; Casagrande, Luca; Fredslund, Mads; Bedding,
Timothy R.; Palle, Pere L.; Antoci, Victoria; Kjeldsen, Hans;
Christensen-Dalsgaard, Jørgen
2017MNRAS.472.4110S Altcode: 2017arXiv170809613S
To better understand how planets form, it is important to study planet
occurrence rates as a function of stellar mass. However, estimating
masses of field stars is often difficult. Over the past decade, a
controversy has arisen about the inferred occurrence rate of gas-giant
planets around evolved intermediate-mass stars - the so-called 'retired
A-stars'. The high masses of these red-giant planet hosts, derived using
spectroscopic information and stellar evolution models, have been called
into question. Here, we address the controversy by determining the
masses of eight evolved planet-hosting stars using asteroseismology. We
compare the masses with spectroscopic-based masses from the Exoplanet
Orbit Database,which were previously adopted to infer properties of
the exoplanets and their hosts. We find a significant one-sided offset
between the two sets of masses for stars with spectroscopic masses
above roughly 1.6 M<SUB>⊙</SUB>, suggestive of an average 15-20
per cent overestimate of the adopted spectroscopic-based masses. The
only star in our sample well below this mass limit is also the only
one not showing this offset. Finally, we note that the scatter across
literature values of spectroscopic-based masses often exceeds their
formal uncertainties, making it comparable to the offset we report here.
---------------------------------------------------------
Title: VizieR Online Data Catalog: 61 main-sequence and subgiant
oscillations (Appourchaux+, 2012)
Authors: Appourchaux, T.; Chaplin, W. J.; Garcia, R. A.; Gruberbauer,
M.; Verner, G. A.; Antia, H. M.; Benomar, O.; Campante, T. L.; Davies,
G. R.; Deheuvels, S.; Handberg, R.; Hekker, S.; Howe, R.; Regulo,
C.; Salabert, D.; Bedding, T. R.; White, T. R.; Ballot, J.; Mathur,
S.; Silva Aguirre, V.; Elsworth, Y. P.; Basu, S.; Gilliland, R. L.;
Christensen-Dalsgaard, J.; Kjeldsen, H.; Uddin, K.; Stumpe, M. C.;
Barclay, T.
2017yCat..35430054A Altcode:
Kepler observations are obtained in two different operating
modes: long cadence (LC) and short cadence (SC) (Gilliland et al.,
2010ApJ...713L.160G; Jenkins et al., 2010ApJ...713L..87J). This work is
based on SC data. For the brightest stars (down to Kepler magnitude,
Kp~=12), SC observations can be obtained for a limited number of
stars (up to 512 at any given time) with a faster sampling cadence
of 58.84876s (Nyquist frequency of ~8.5mHz), which permits a more
precise transit timing and the performance of asteroseismology. Kepler
observations are divided into three-month-long quarters (Q). A subset
of 61 solar-type stars observed during quarters Q5-Q7 (March 22,
2010 to December 22, 2010) were chosen because they have oscillation
modes with high signal-to-noise ratios. This length of data gives a
frequency resolution of about 0.04uHz. <P />(2 data files).
---------------------------------------------------------
Title: Erratum: “Standing on the Shoulders of Dwarfs: The Kepler
Asteroseismic LEGACY Sample. I. Oscillation Mode Parameters”
(<A href="https://doi.org/10.3847/1538-4357/835/2/172">2017, ApJ,
835, 172</A>)
Authors: Lund, Mikkel N.; Silva Aguirre, Víctor; Davies, Guy R.;
Chaplin, William J.; Christensen-Dalsgaard, Jørgen; Houdek, Günter;
White, Timothy R.; Bedding, Timothy R.; Ball, Warrick H.; Huber,
Daniel; Antia, H. M.; Lebreton, Yveline; Latham, David W.; Handberg,
Rasmus; Verma, Kuldeep; Basu, Sarbani; Casagrande, Luca; Justesen,
Anders B.; Kjeldsen, Hans; Mosumgaard, Jakob R.
2017ApJ...850..110L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A semi-analytical computation of the theoretical uncertainties
of the solar neutrino flux
Authors: Jørgensen, Andreas C. S.; Christensen-Dalsgaard, Jørgen
2017MNRAS.471.4802J Altcode: 2018arXiv180809153C
We present a comparison between Monte Carlo simulations and a
semi-analytical approach that reproduces the theoretical probability
distribution functions of the solar neutrino fluxes, stemming from
the pp, pep, hep, <SUP>7</SUP>Be, <SUP>8</SUP>B, <SUP>13</SUP>N,
<SUP>15</SUP>O and <SUP>17</SUP>F source reactions. We obtain good
agreement between the two approaches. Thus, the semi-analytical method
yields confidence intervals that closely match those found, based on
Monte Carlo simulations, and points towards the same general symmetries
of the investigated probability distribution functions. Furthermore, the
negligible computational cost of this method is a clear advantage over
Monte Carlo simulations, making it trivial to take new observational
constraints on the input parameters into account.
---------------------------------------------------------
Title: Improving 1D Stellar Models with 3D Atmospheres
Authors: Mosumgaard, Jakob Rørsted; Silva Aguirre, Víctor; Weiss,
Achim; Christensen-Dalsgaard, Jørgen; Trampedach, Regner
2017EPJWC.16003009M Altcode: 2016arXiv161007323R; 2017EPJWC.16003009R; 2016arXiv161007323M
Stellar evolution codes play a major role in present-day astrophysics,
yet they share common issues. In this work we seek to remedy some
of those by the use of results from realistic and highly detailed 3D
hydrodynamical simulations of stellar atmospheres. We have implemented
a new temperature stratification extracted directly from the 3D
simulations into the Garching Stellar Evolution Code to replace the
simplified atmosphere normally used. Secondly, we have implemented
the use of a variable mixing-length parameter, which changes as a
function of the stellar surface gravity and temperature - also derived
from the 3D simulations. Furthermore, to make our models consistent,
we have calculated new opacity tables to match the atmospheric
simulations. Here, we present the modified code and initial results
on stellar evolution using it.
---------------------------------------------------------
Title: Foreword
Authors: Christensen-Dalsgaard, Jørgen
2017EPJWC.16000002C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A fitting LEGACY - modelling Kepler's best stars
Authors: Aarslev, Magnus J.; Christensen-Dalsgaard, Jørgen; Lund,
Mikkel N.; Silva Aguirre, Victor; Gough, Douglas
2017EPJWC.16003010A Altcode:
The LEGACY sample represents the best solar-like stars observed in
the Kepler mission[5, 8]. The 66 stars in the sample are all on
the main sequence or only slightly more evolved. They each have
more than one year's observation data in short cadence, allowing
for precise extraction of individual frequencies. Here we present
model fits using a modified ASTFIT procedure employing two different
near-surface-effect corrections, one by Christensen-Dalsgaard[4] and
a newer correction proposed by Ball & Gizon[1]. We then compare
the results obtained using the different corrections. We find that
using the latter correction yields lower masses and significantly
lower χ<SUP>2</SUP> values for a large part of the sample.
---------------------------------------------------------
Title: Promoting access to and use of seismic data in a large
scientific community. SpaceInn data handling and archiving
Authors: Michel, Eric; Belkacem, Kevin; Samadi, Reza; Assis Peralta,
Raphael de; Renié, Christian; Abed, Mahfoudh; Lin, Guangyuan;
Christensen-Dalsgaard, Jørgen; Houdek, Günter; Handberg, Rasmus;
Gizon, Laurent; Burston, Raymond; Nagashima, Kaori; Pallé, Pere;
Poretti, Ennio; Rainer, Monica; Mistò, Angelo; Panzera, Maria Rosa;
Roth, Markus
2017EPJWC.16001011M Altcode:
The growing amount of seismic data available from space missions
(SOHO, CoRoT, Kepler, SDO,…) but also from ground-based facilities
(GONG, BiSON, ground-based large programmes…), stellar modelling
and numerical simulations, creates new scientific perspectives such as
characterizing stellar populations in our Galaxy or planetary systems
by providing model-independent global properties of stars such as mass,
radius, and surface gravity within several percent accuracy, as well as
constraints on the age. These applications address a broad scientific
community beyond the solar and stellar one and require combining
indices elaborated with data from different databases (e.g. seismic
archives and ground-based spectroscopic surveys). It is thus a basic
requirement to develop a simple and effcient access to these various
data resources and dedicated tools. In the framework of the European
project SpaceInn (FP7), several data sources have been developed or
upgraded. The Seismic Plus Portal has been developed, where synthetic
descriptions of the most relevant existing data sources can be found,
as well as tools allowing to localize existing data for given objects
or period and helping the data query. This project has been developed
within the Virtual Observatory (VO) framework. In this paper, we
give a review of the various facilities and tools developed within
this programme. The SpaceInn project (Exploitation of Space Data for
Innovative Helio- and Asteroseismology) has been initiated by the
European Helio- and Asteroseismology Network (HELAS).
---------------------------------------------------------
Title: A view into the core of α Cen A
Authors: Bazot, Michaël; Christensen-Dalsgaard, Jørgen; Benomar,
Othman; Gizon, Laurent
2017EPJWC.16003006B Altcode:
We present results of modelling of α Cen A. In order to estimate
the physical parameters of this star, we modelled spectroscopic,
interferometric, astrometric and asteroseismic data. To that effect we
chose to use a Bayesian approach to parameter estimation, which allowed
us, in particular, to define our prior knowledge on the parameters. An
important question we wanted to address was to assess whether or not
α Cen A has a convective core. We found that the data we used give
indecisive results on this issue. If the star has a convective core,
and provided that overshooting is taken into account, there is a
possibility for the star to be in the peculiar state in which the ppII
chain is the main driver of nuclear energy generation. We also found
a non-negligible probability for α Cen A to be a very early subgiant.
---------------------------------------------------------
Title: Data preparation for asteroseismology with TESS
Authors: Lund, Mikkel N.; Handberg, Rasmus; Kjeldsen, Hans; Chaplin,
William J.; Christensen-Dalsgaard, Jørgen
2017EPJWC.16001005L Altcode: 2016arXiv161002702L
The Transiting Exoplanet Survey Satellite (TESS) is a NASA Astrophysics
Explorer mission. Following its scheduled launch in 2017, TESS will
focus on detecting exoplanets around the nearest and brightest stars in
the sky, for which detailed follow-up observations are possible. TESS
will, as the NASA Kepler mission, include a asteroseismic program that
will be organized within the TESS Asteroseismic Science Consortium
(TASC), building on the success of the Kepler Asteroseismic Science
Consortium (KASC). Within TASC data for asteroseismic analysis will be
prepared by the TASC Working Group 0 (WG-0), who will facilitate data
to the community via the TESS Asteroseismic Science Operations Center
(TASOC), again building on the success of the corresponding KASOC
platform for Kepler. Here, we give an overview of the steps being
taken within WG-0 to prepare for the upcoming TESS mission.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Kepler LEGACY stars high-precision
abundances (Nissen+, 2017)
Authors: Nissen, P. E.; Silva Aguirre, V.; Christensen-Dalsgaard,
J.; Collet, R.; Grundahl, F.; Slumstrup, D.
2017yCat..36080112N Altcode:
Stellar parameters are given in Table 1 and abundance ratios relative
to Fe in Table 2. <P />(2 data files).
---------------------------------------------------------
Title: VizieR Online Data Catalog: Kepler asteroseismic LEGACY
sample. I. Oscillations (Lund+, 2017)
Authors: Lund, M. N.; Silva Aguirre, V.; Davies, G. R.; Chaplin,
W. J.; Christensen-Dalsgaard, J.; Houdek, G.; White, T. R.; Bedding,
T. R.; Ball, W. H.; Huber, D.; Antia, H. M.; Lebreton, Y.; Latham,
D. W.; Handberg, R.; Verma, K.; Basu, S.; Casagrande, L.; Justesen,
A. B.; Kjeldsen, H.; Mosumgaard, J. R.
2017yCat..18350172L Altcode:
The advent of space-based missions like Kepler has revolutionized the
study of solar-type stars, particularly through the measurement and
modeling of their resonant modes of oscillation. Here we analyze
a sample of 66 Kepler main-sequence stars showing solar-like
oscillations as part of the Kepler seismic LEGACY project. We use
Kepler short-cadence data, of which each star has at least 12 months,
to create frequency-power spectra optimized for asteroseismology. For
each star, we identify its modes of oscillation and extract parameters
such as frequency, amplitude, and line width using a Bayesian Markov
chain Monte Carlo "peak-bagging" approach. We report the extracted
mode parameters for all 66 stars, as well as derived quantities such
as frequency difference ratios, the large and small separations Δν
and δν<SUB>02</SUB>; the behavior of line widths with frequency
and line widths at ν<SUB>max</SUB> with T<SUB>eff</SUB>, for which
we derive parametrizations; and behavior of mode visibilities. These
average properties can be applied in future peak-bagging exercises to
better constrain the parameters of the stellar oscillation spectra. The
frequencies and frequency ratios can tightly constrain the fundamental
parameters of these solar-type stars, and mode line widths and
amplitudes can test models of mode damping and excitation. <P />(4
data files).
---------------------------------------------------------
Title: VizieR Online Data Catalog: Kepler asteroseismic LEGACY
sample. II. (Silva Aguirre+, 2017)
Authors: Silva Aguirre, V.; Lund, M. N.; Antia, H. M.; Ball, W. H.;
Basu, S.; Christensen-Dalsgaard, J.; Lebreton, Y.; Reese, D. R.; Verma,
K.; Casagrande, L.; Justesen, A. B.; Mosumgaard, J. R.; Chaplin, W. J.;
Bedding, T. R.; Davies, G. R.; Handberg, R.; Houdek, G.; Huber, D.;
Kjeldsen, H.; Latham, D. W.; White, T. R.; Coelho, H. R.; Miglio,
A.; Rendle, B.
2017yCat..18350173S Altcode:
The 66 stars comprising the LEGACY sample were chosen from more than 500
main-sequence and subgiant targets in which Kepler detected oscillations
(Chaplin+ 2014, J/ApJS/210/1). We selected all targets that had more
than one year of short-cadence observations, and where inspection of
the power spectrum did not reveal any clear signature of bumped l=1
modes. <P />(3 data files).
---------------------------------------------------------
Title: PLATO as it is : A legacy mission for Galactic archaeology
Authors: Miglio, A.; Chiappini, C.; Mosser, B.; Davies, G. R.;
Freeman, K.; Girardi, L.; Jofré, P.; Kawata, D.; Rendle, B. M.;
Valentini, M.; Casagrande, L.; Chaplin, W. J.; Gilmore, G.; Hawkins,
K.; Holl, B.; Appourchaux, T.; Belkacem, K.; Bossini, D.; Brogaard,
K.; Goupil, M. -J.; Montalbán, J.; Noels, A.; Anders, F.; Rodrigues,
T.; Piotto, G.; Pollacco, D.; Rauer, H.; Prieto, C. Allende; Avelino,
P. P.; Babusiaux, C.; Barban, C.; Barbuy, B.; Basu, S.; Baudin, F.;
Benomar, O.; Bienaymé, O.; Binney, J.; Bland-Hawthorn, J.; Bressan,
A.; Cacciari, C.; Campante, T. L.; Cassisi, S.; Christensen-Dalsgaard,
J.; Combes, F.; Creevey, O.; Cunha, M. S.; Jong, R. S.; Laverny, P.;
Degl'Innocenti, S.; Deheuvels, S.; Depagne, É.; Ridder, J.; Matteo,
P. Di; Mauro, M. P. Di; Dupret, M. -A.; Eggenberger, P.; Elsworth,
Y.; Famaey, B.; Feltzing, S.; García, R. A.; Gerhard, O.; Gibson,
B. K.; Gizon, L.; Haywood, M.; Handberg, R.; Heiter, U.; Hekker,
S.; Huber, D.; Ibata, R.; Katz, D.; Kawaler, S. D.; Kjeldsen, H.;
Kurtz, D. W.; Lagarde, N.; Lebreton, Y.; Lund, M. N.; Majewski, S. R.;
Marigo, P.; Martig, M.; Mathur, S.; Minchev, I.; Morel, T.; Ortolani,
S.; Pinsonneault, M. H.; Plez, B.; Moroni, P. G. Prada; Pricopi, D.;
Recio-Blanco, A.; Reylé, C.; Robin, A.; Roxburgh, I. W.; Salaris,
M.; Santiago, B. X.; Schiavon, R.; Serenelli, A.; Sharma, S.; Aguirre,
V. Silva; Soubiran, C.; Steinmetz, M.; Stello, D.; Strassmeier, K. G.;
Ventura, P.; Ventura, R.; Walton, N. A.; Worley, C. C.
2017AN....338..644M Altcode: 2017arXiv170603778M
Deciphering the assembly history of the Milky Way is a formidable
task, which becomes possible only if one can produce high-resolution
chrono-chemo-kinematical maps of the Galaxy. Data from large-scale
astrometric and spectroscopic surveys will soon provide us with a
well-defined view of the current chemo-kinematical structure of the
Milky Way, but will only enable a blurred view on the temporal sequence
that led to the present-day Galaxy. As demonstrated by the (ongoing)
exploitation of data from the pioneering photometric missions CoRoT,
Kepler, and K2, asteroseismology provides the way forward: solar-like
oscillating giants are excellent evolutionary clocks thanks to the
availability of seismic constraints on their mass and to the tight
age-initial-mass relation they adhere to. In this paper we identify
five key outstanding questions relating to the formation and evolution
of the Milky Way that will need precise and accurate ages for large
samples of stars to be addressed, and we identify the requirements
in terms of number of targets and the precision on the stellar
properties that are needed to tackle such questions. By quantifying
the asteroseismic yields expected from PLATO for red-giant stars, we
demonstrate that these requirements are within the capabilities of the
current instrument design, provided that observations are sufficiently
long to identify the evolutionary state and allow robust and precise
determination of acoustic-mode frequencies. This will allow us to
harvest data of sufficient quality to reach a 10% precision in age. This
is a fundamental pre-requisite to then reach the more ambitious goal
of a similar level of accuracy, which will only be possible if we
have to hand a careful appraisal of systematic uncertainties on age
deriving from our limited understanding of stellar physics, a goal
which conveniently falls within the main aims of PLATO's core science.
---------------------------------------------------------
Title: Kepler sheds new and unprecedented light on the variability
of a blue supergiant: Gravity waves in the O9.5Iab star HD 188209
Authors: Aerts, C.; Símon-Díaz, S.; Bloemen, S.; Debosscher, J.;
Pápics, P. I.; Bryson, S.; Still, M.; Moravveji, E.; Williamson,
M. H.; Grundahl, F.; Fredslund Andersen, M.; Antoci, V.; Pallé,
P. L.; Christensen-Dalsgaard, J.; Rogers, T. M.
2017A&A...602A..32A Altcode: 2017arXiv170301514A
Stellar evolution models are most uncertain for evolved massive
stars. Asteroseismology based on high-precision uninterrupted space
photometry has become a new way to test the outcome of stellar
evolution theory and was recently applied to a multitude of stars,
but not yet to massive evolved supergiants.Our aim is to detect,
analyse and interpret the photospheric and wind variability of the
O9.5 Iab star HD 188209 from Kepler space photometry and long-term
high-resolution spectroscopy. We used Kepler scattered-light photometry
obtained by the nominal mission during 1460 d to deduce the photometric
variability of this O-type supergiant. In addition, we assembled
and analysed high-resolution high signal-to-noise spectroscopy taken
with four spectrographs during some 1800 d to interpret the temporal
spectroscopic variability of the star. The variability of this blue
supergiant derived from the scattered-light space photometry is in full
in agreement with the one found in the ground-based spectroscopy. We
find significant low-frequency variability that is consistently detected
in all spectral lines of HD 188209. The photospheric variability
propagates into the wind, where it has similar frequencies but slightly
higher amplitudes. The morphology of the frequency spectra derived from
the long-term photometry and spectroscopy points towards a spectrum
of travelling waves with frequency values in the range expected for
an evolved O-type star. Convectively-driven internal gravity waves
excited in the stellar interior offer the most plausible explanation
of the detected variability. <P />Based on photometric observations
made with the NASA Kepler satellite and on spectroscopic observations
made with four telescopes: the Nordic Optical Telescope operated by
NOTSA and the Mercator Telescope operated by the Flemish Community,
both at the Observatorio del Roque de los Muchachos (La Palma, Spain)
of the Instituto de Astrofísica de Canarias, the T13 2.0 m Automatic
Spectroscopic Telescope (AST) operated by Tennessee State University at
the Fairborn Observatory, and the Hertzsprung SONG telescope operated
on the Spanish Observatorio del Teide on the island of Tenerife by the
Aarhus and Copenhagen Universities and by the Instituto de Astrofísica
de Canarias, Spain.
---------------------------------------------------------
Title: Giant star seismology
Authors: Hekker, S.; Christensen-Dalsgaard, J.
2017A&ARv..25....1H Altcode: 2016arXiv160907487H
The internal properties of stars in the red-giant phase
undergo significant changes on relatively short timescales. Long
near-uninterrupted high-precision photometric timeseries observations
from dedicated space missions such as CoRoT and Kepler have provided
seismic inferences of the global and internal properties of a large
number of evolved stars, including red giants. These inferences are
confronted with predictions from theoretical models to improve our
understanding of stellar structure and evolution. Our knowledge and
understanding of red giants have indeed increased tremendously using
these seismic inferences, and we anticipate that more information is
still hidden in the data. Unraveling this will further improve our
understanding of stellar evolution. This will also have significant
impact on our knowledge of the Milky Way Galaxy as well as on exo-planet
host stars. The latter is important for our understanding of the
formation and structure of planetary systems.
---------------------------------------------------------
Title: Kepler observations of the asteroseismic binary HD 176465
Authors: White, T. R.; Benomar, O.; Silva Aguirre, V.; Ball, W. H.;
Bedding, T. R.; Chaplin, W. J.; Christensen-Dalsgaard, J.; Garcia,
R. A.; Gizon, L.; Stello, D.; Aigrain, S.; Antia, H. M.; Appourchaux,
T.; Bazot, M.; Campante, T. L.; Creevey, O. L.; Davies, G. R.;
Elsworth, Y. P.; Gaulme, P.; Handberg, R.; Hekker, S.; Houdek,
G.; Howe, R.; Huber, D.; Karoff, C.; Marques, J. P.; Mathur, S.;
McQuillan, A.; Metcalfe, T. S.; Mosser, B.; Nielsen, M. B.; Régulo,
C.; Salabert, D.; Stahn, T.
2017A&A...601A..82W Altcode: 2016arXiv160909581W; 2016A&A...601A..82W
Binary star systems are important for understanding stellar structure
and evolution, and are especially useful when oscillations can be
detected and analysed with asteroseismology. However, only four
systems are known in which solar-like oscillations are detected in
both components. Here, we analyse the fifth such system, HD 176465,
which was observed by Kepler. We carefully analysed the system's
power spectrum to measure individual mode frequencies, adapting our
methods where necessary to accommodate the fact that both stars
oscillate in a similar frequency range. We also modelled the two
stars independently by fitting stellar models to the frequencies and
complementaryparameters. We are able to cleanly separate the oscillation
modes in both systems. The stellar models produce compatible ages and
initial compositions for the stars, as is expected from their common
and contemporaneous origin. Combining the individual ages, the system
is about 3.0 ± 0.5 Gyr old. The two components of HD 176465 are young
physically-similar oscillating solar analogues, the first such system
to be found, and provide important constraints for stellar evolution
and asteroseismology.
---------------------------------------------------------
Title: The asteroseismic surface effect from a grid of 3D convection
simulations - I. Frequency shifts from convective expansion of
stellar atmospheres
Authors: Trampedach, Regner; Aarslev, Magnus J.; Houdek, Günter;
Collet, Remo; Christensen-Dalsgaard, Jørgen; Stein, Robert F.;
Asplund, Martin
2017MNRAS.466L..43T Altcode: 2016arXiv161102638T
We analyse the effect on adiabatic stellar oscillation frequencies
of replacing the near-surface layers in 1D stellar structure models
with averaged 3D stellar surface convection simulations. The main
difference is an expansion of the atmosphere by 3D convection,
expected to explain a major part of the asteroseismic surface effect,
a systematic overestimation of p-mode frequencies due to inadequate
surface physics. We employ pairs of 1D stellar envelope models and 3D
simulations from a previous calibration of the mixing-length parameter,
α. That calibration constitutes the hitherto most consistent matching
of 1D models to 3D simulations, ensuring that their differences are not
spurious, but entirely due to the 3D nature of convection. The resulting
frequency shift is identified as the structural part of the surface
effect. The important, typically non-adiabatic, modal components of
the surface effect are not included in this analysis, but relegated to
future papers. Evaluating the structural surface effect at the frequency
of maximum mode amplitude, ν<SUB>max </SUB>, we find shifts from δν =
-0.8 μHz for giants at log g = 2.2 to - 35 μHz for a (T<SUB>eff</SUB>
= 6901 K, log g = 4.29) dwarf. The fractional effect δν(ν<SUB>max
</SUB>)/ν<SUB>max </SUB>, ranges from -0.1 per cent for a cool dwarf
(4185 K, 4.74) to -6 per cent for a warm giant (4962 K, 2.20).
---------------------------------------------------------
Title: Standing on the Shoulders of Dwarfs: the Kepler Asteroseismic
LEGACY Sample. I. Oscillation Mode Parameters
Authors: Lund, Mikkel N.; Silva Aguirre, Víctor; Davies, Guy R.;
Chaplin, William J.; Christensen-Dalsgaard, Jørgen; Houdek, Günter;
White, Timothy R.; Bedding, Timothy R.; Ball, Warrick H.; Huber,
Daniel; Antia, H. M.; Lebreton, Yveline; Latham, David W.; Handberg,
Rasmus; Verma, Kuldeep; Basu, Sarbani; Casagrande, Luca; Justesen,
Anders B.; Kjeldsen, Hans; Mosumgaard, Jakob R.
2017ApJ...835..172L Altcode: 2016arXiv161200436L
The advent of space-based missions like Kepler has revolutionized the
study of solar-type stars, particularly through the measurement and
modeling of their resonant modes of oscillation. Here we analyze
a sample of 66 Kepler main-sequence stars showing solar-like
oscillations as part of the Kepler seismic LEGACY project. We use
Kepler short-cadence data, of which each star has at least 12 months, to
create frequency-power spectra optimized for asteroseismology. For each
star, we identify its modes of oscillation and extract parameters
such as frequency, amplitude, and line width using a Bayesian
Markov chain Monte Carlo “peak-bagging” approach. We report
the extracted mode parameters for all 66 stars, as well as derived
quantities such as frequency difference ratios, the large and small
separations {{Δ }}ν and δ {ν }<SUB>02</SUB>; the behavior of
line widths with frequency and line widths at {ν }<SUB>\max </SUB>
with {T}<SUB>{eff</SUB>}, for which we derive parametrizations; and
behavior of mode visibilities. These average properties can be applied
in future peak-bagging exercises to better constrain the parameters of
the stellar oscillation spectra. The frequencies and frequency ratios
can tightly constrain the fundamental parameters of these solar-type
stars, and mode line widths and amplitudes can test models of mode
damping and excitation.
---------------------------------------------------------
Title: Standing on the Shoulders of Dwarfs: the Kepler Asteroseismic
LEGACY Sample. II.Radii, Masses, and Ages
Authors: Silva Aguirre, Víctor; Lund, Mikkel N.; Antia, H. M.; Ball,
Warrick H.; Basu, Sarbani; Christensen-Dalsgaard, Jørgen; Lebreton,
Yveline; Reese, Daniel R.; Verma, Kuldeep; Casagrande, Luca; Justesen,
Anders B.; Mosumgaard, Jakob R.; Chaplin, William J.; Bedding, Timothy
R.; Davies, Guy R.; Handberg, Rasmus; Houdek, Günter; Huber, Daniel;
Kjeldsen, Hans; Latham, David W.; White, Timothy R.; Coelho, Hugo R.;
Miglio, Andrea; Rendle, Ben
2017ApJ...835..173S Altcode: 2016arXiv161108776S
We use asteroseismic data from the Kepler satellite to determine
fundamental stellar properties of the 66 main-sequence targets
observed for at least one full year by the mission. We distributed
tens of individual oscillation frequencies extracted from the time
series of each star among seven modeling teams who applied different
methods to determine radii, masses, and ages for all stars in the
sample. Comparisons among the different results reveal a good level of
agreement in all stellar properties, which is remarkable considering
the variety of codes, input physics, and analysis methods employed
by the different teams. Average uncertainties are of the order
of ∼2% in radius, ∼4% in mass, and ∼10% in age, making this
the best-characterized sample of main-sequence stars available to
date. Our predicted initial abundances and mixing-length parameters
are checked against inferences from chemical enrichment laws ΔY/ΔZ
and predictions from 3D atmospheric simulations. We test the accuracy
of the determined stellar properties by comparing them to the Sun,
angular diameter measurements, Gaia parallaxes, and binary evolution,
finding excellent agreement in all cases and further confirming the
robustness of asteroseismically determined physical parameters of stars
when individual frequencies of oscillation are available. Baptised
as the Kepler dwarfs LEGACY sample, these stars are the solar-like
oscillators with the best asteroseismic properties available for at
least another decade. All data used in this analysis and the resulting
stellar parameters are made publicly available for the community.
---------------------------------------------------------
Title: First Results from the Hertzsprung SONG Telescope:
Asteroseismology of the G5 Subgiant Star μ Herculis
Authors: Grundahl, F.; Fredslund Andersen, M.; Christensen-Dalsgaard,
J.; Antoci, V.; Kjeldsen, H.; Handberg, R.; Houdek, G.; Bedding, T. R.;
Pallé, P. L.; Jessen-Hansen, J.; Silva Aguirre, V.; White, T. R.;
Frandsen, S.; Albrecht, S.; Andersen, M. I.; Arentoft, T.; Brogaard,
K.; Chaplin, W. J.; Harpsøe, K.; Jørgensen, U. G.; Karovicova, I.;
Karoff, C.; Kjærgaard Rasmussen, P.; Lund, M. N.; Sloth Lundkvist,
M.; Skottfelt, J.; Norup Sørensen, A.; Tronsgaard, R.; Weiss, E.
2017ApJ...836..142G Altcode: 2017arXiv170103365G
We report the first asteroseismic results obtained with the Hertzsprung
Stellar Observations Network Group Telescope from an extensive
high-precision radial-velocity observing campaign of the subgiant μ
Herculis. The data set was collected during 215 nights in 2014 and
2015. We detected a total of 49 oscillation modes with l values from
zero to three, including some l = 1 mixed modes. Based on the rotational
splitting observed in l = 1 modes, we determine a rotational period of
52 days and a stellar inclination angle of 63°. The parameters obtained
through modeling of the observed oscillation frequencies agree very well
with independent observations and imply a stellar mass between 1.11 and
1.15 M <SUB>⊙</SUB> and an age of {7.8}<SUB>-0.4</SUB><SUP>+0.3</SUP>
Gyr. Furthermore, the high-quality data allowed us to determine the
acoustic depths of the He II ionization layer and the base of the
convection zone. <P />Based on observations made with the Hertzsprung
SONG telescope operated on the Spanish Observatorio del Teide on the
island of Tenerife by the Aarhus and Copenhagen Universities and by
the Instituto de Astrofísica de Canarias.
---------------------------------------------------------
Title: Testing stellar evolution models with the retired A star
HD 185351
Authors: Hjørringgaard, J. G.; Silva Aguirre, V.; White, T. R.;
Huber, D.; Pope, B. J. S.; Casagrande, L.; Justesen, A. B.;
Christensen-Dalsgaard, J.
2017MNRAS.464.3713H Altcode: 2016MNRAS.tmp.1542H; 2016arXiv161005990H
The physical parameters of the retired A star HD 185351 were analysed in
great detail by Johnson et al. using interferometry, spectroscopy, and
asteroseismology. Results from all independent methods are consistent
with HD 185351 having a mass in excess of 1.5 M<SUB>⊙</SUB>. However,
the study also showed that not all observational constraints could be
reconciled in stellar evolutionary models, leading to mass estimates
ranging from ∼1.6 to 1.9 M<SUB>⊙</SUB> and casting doubts on the
accuracy of stellar properties determined from asteroseismology. Here,
we solve this discrepancy and construct a theoretical model in agreement
with all observational constraints on the physical parameters of HD
185351. The effects of varying input physics are examined as well as
the additional constraint of the observed g-mode period spacing is
considered. This quantity is found to be sensitive to the inclusion of
additional mixing from the convective core during the main sequence,
and can be used to calibrate the overshooting efficiency using
low-luminosity red giant stars. A theoretical model with metallicity
[Fe/H] = 0.16 dex, mixing-length parameter α<SUB>MLT</SUB> = 2.00,
and convective overshooting efficiency parameter f = 0.030 is found
to be in complete agreement with all observational constraints for a
stellar mass of M ≃ 1.60 M<SUB>⊙</SUB>.
---------------------------------------------------------
Title: On the surface physics affecting solar oscillation frequencies
Authors: Houdek, G.; Trampedach, R.; Aarslev, M. J.;
Christensen-Dalsgaard, J.
2017MNRAS.464L.124H Altcode: 2016arXiv160906129H
Adiabatic oscillation frequencies of stellar models, computed with the
standard mixing-length formulation for convection, increasingly deviate
with radial order from observations in solar-like stars. Standard
solar models overestimate adiabatic frequencies by as much as ∼ 20
μHz. In this Letter, we address the physical processes of turbulent
convection that are predominantly responsible for the frequency
differences between standard models and observations, also called
`surface effects'. We compare measured solar frequencies from the
Michelson Doppler Imager instrument on the SOlar and Heliospheric
Observatory spacecraft with frequency calculations that include
3D hydrodynamical simulation results in the equilibrium model,
non-adiabatic effects, and a consistent treatment of the turbulent
pressure in both the equilibrium and stability computations. With the
consistent inclusion of the above physics in our model computation,
we are able to reproduce the observed solar frequencies to ≲3 μHz
without the need of any additional ad hoc functional corrections.
---------------------------------------------------------
Title: Asteroseismic Properties of Solar-type Stars Observed with
the NASA K2 Mission: Results from Campaigns 1-3 and Prospects for
Future Observations
Authors: Lund, Mikkel N.; Chaplin, William J.; Casagrande,
Luca; Silva Aguirre, Víctor; Basu, Sarbani; Bieryla, Allyson;
Christensen-Dalsgaard, Jørgen; Latham, David W.; White, Timothy R.;
Davies, Guy R.; Huber, Daniel; Buchhave, Lars A.; Handberg, Rasmus
2016PASP..128l4204L Altcode: 2016arXiv160807292L
We present an asteroseismic analysis of 33 solar-type stars observed in
short cadence (SC) during Campaigns (C) 1-3 of the NASA K2 mission. We
were able to extract both average seismic parameters and individual mode
frequencies for stars with dominant frequencies up to ∼3300 μHz,
and we find that data for some targets are good enough to allow for
a measurement of the rotational splitting. Modeling of the extracted
parameters is performed by using grid-based methods using average
parameters and individual frequencies together with spectroscopic
parameters. For the target selection in C3, stars were chosen as in C1
and C2 to cover a wide range in parameter space to better understand
the performance and noise characteristics. For C3 we still detected
oscillations in 73% of the observed stars that we proposed. Future K2
campaigns hold great promise for the study of nearby clusters and the
chemical evolution and age-metallicity relation of nearby field stars in
the solar neighborhood. We expect oscillations to be detected in ∼388
SC targets if the K2 mission continues until C18, which will greatly
complement the ∼500 detections of solar-like oscillations made for
SC targets during the nominal Kepler mission. For ∼30-40 of these,
including several members of the Hyades open cluster, we furthermore
expect that inference from interferometry should be possible.
---------------------------------------------------------
Title: Detection of Solar-like Oscillations, Observational
Constraints, and Stellar Models for θ Cyg, the Brightest Star
Observed By the Kepler Mission
Authors: Guzik, J. A.; Houdek, G.; Chaplin, W. J.; Smalley, B.; Kurtz,
D. W.; Gilliland, R. L.; Mullally, F.; Rowe, J. F.; Bryson, S. T.;
Still, M. D.; Antoci, V.; Appourchaux, T.; Basu, S.; Bedding, T. R.;
Benomar, O.; Garcia, R. A.; Huber, D.; Kjeldsen, H.; Latham, D. W.;
Metcalfe, T. S.; Pápics, P. I.; White, T. R.; Aerts, C.; Ballot, J.;
Boyajian, T. S.; Briquet, M.; Bruntt, H.; Buchhave, L. A.; Campante,
T. L.; Catanzaro, G.; Christensen-Dalsgaard, J.; Davies, G. R.;
Doğan, G.; Dragomir, D.; Doyle, A. P.; Elsworth, Y.; Frasca, A.;
Gaulme, P.; Gruberbauer, M.; Handberg, R.; Hekker, S.; Karoff, C.;
Lehmann, H.; Mathias, P.; Mathur, S.; Miglio, A.; Molenda-Żakowicz,
J.; Mosser, B.; Murphy, S. J.; Régulo, C.; Ripepi, V.; Salabert,
D.; Sousa, S. G.; Stello, D.; Uytterhoeven, K.
2016ApJ...831...17G Altcode: 2016arXiv160701035G
θ Cygni is an F3 spectral type magnitude V = 4.48 main-sequence star
that was the brightest star observed by the original Kepler spacecraft
mission. Short-cadence (58.8 s) photometric data using a custom
aperture were first obtained during Quarter 6 (2010 June-September) and
subsequently in Quarters 8 and 12-17. We present analyses of solar-like
oscillations based on Q6 and Q8 data, identifying angular degree l = 0,
1, and 2 modes with frequencies of 1000-2700 μHz, a large frequency
separation of 83.9 ± 0.4 μHz, and maximum oscillation amplitude
at frequency ν <SUB>max</SUB> = 1829 ± 54 μHz. We also present
analyses of new ground-based spectroscopic observations, which,
combined with interferometric angular diameter measurements, give T
<SUB>eff</SUB> = 6697 ± 78 K, radius 1.49 ± 0.03 R <SUB>⊙</SUB>,
[Fe/H] = -0.02 ± 0.06 dex, and log g = 4.23 ± 0.03. We calculate
stellar models matching these constraints using the Yale Rotating
Evolution Code and the Asteroseismic Modeling Portal. The best-fit
models have masses of 1.35-1.39 M <SUB>⊙</SUB> and ages of 1.0-1.6
Gyr. θ Cyg’s T <SUB>eff</SUB> and log g place it cooler than the red
edge of the γ Doradus instability region established from pre-Kepler
ground-based observations, but just at the red edge derived from
pulsation modeling. The pulsation models show γ Dor gravity modes
driven by the convective blocking mechanism, with frequencies of 1-3
cycles per day (11 to 33 μHz). However, gravity modes were not seen
in Kepler data; one signal at 1.776 cycles per day (20.56 μHz) may
be attributable to a faint, possibly background, binary.
---------------------------------------------------------
Title: The Asteroseismic Potential of TESS: Exoplanet-host Stars
Authors: Campante, T. L.; Schofield, M.; Kuszlewicz, J. S.; Bouma,
L.; Chaplin, W. J.; Huber, D.; Christensen-Dalsgaard, J.; Kjeldsen,
H.; Bossini, D.; North, T. S. H.; Appourchaux, T.; Latham, D. W.;
Pepper, J.; Ricker, G. R.; Stassun, K. G.; Vanderspek, R.; Winn, J. N.
2016ApJ...830..138C Altcode: 2016arXiv160801138C
New insights on stellar evolution and stellar interior physics are
being made possible by asteroseismology. Throughout the course of the
Kepler mission, asteroseismology has also played an important role
in the characterization of exoplanet-host stars and their planetary
systems. The upcoming NASA Transiting Exoplanet Survey Satellite
(TESS) will be performing a near all-sky survey for planets that
transit bright nearby stars. In addition, its excellent photometric
precision, combined with its fine time sampling and long intervals of
uninterrupted observations, will enable asteroseismology of solar-type
and red-giant stars. Here we develop a simple test to estimate the
detectability of solar-like oscillations in TESS photometry of any given
star. Based on an all-sky stellar and planetary synthetic population,
we go on to predict the asteroseismic yield of the TESS mission,
placing emphasis on the yield of exoplanet-host stars for which we
expect to detect solar-like oscillations. This is done for both the
target stars (observed at a 2-minute cadence) and the full-frame-image
stars (observed at a 30-minute cadence). A similar exercise is also
conducted based on a compilation of known host stars. We predict that
TESS will detect solar-like oscillations in a few dozen target hosts
(mainly subgiant stars but also in a smaller number of F dwarfs), in up
to 200 low-luminosity red-giant hosts, and in over 100 solar-type and
red-giant known hosts, thereby leading to a threefold improvement in the
asteroseismic yield of exoplanet-host stars when compared to Kepler's.
---------------------------------------------------------
Title: Towards 21st century stellar models: Star clusters,
supercomputing and asteroseismology
Authors: Campbell, S. W.; Constantino, T. N.; D'Orazi, V.; Meakin,
C.; Stello, D.; Christensen-Dalsgaard, J.; Kuehn, C.; De Silva, G. M.;
Arnett, W. D.; Lattanzio, J. C.; MacLean, B. T.
2016AN....337..788C Altcode: 2015arXiv151204774C
Stellar models provide a vital basis for many aspects of astronomy
and astrophysics. Recent advances in observational astronomy - through
asteroseismology, precision photometry, high-resolution spectroscopy,
and large-scale surveys - are placing stellar models under greater
quantitative scrutiny than ever. The model limitations are being
exposed and the next generation of stellar models is needed as soon
as possible. The current uncertainties in the models propagate to
the later phases of stellar evolution, hindering our understanding
of stellar populations and chemical evolution. Here we give a brief
overview of the evolution, importance, and substantial uncertainties
of core helium burning stars in particular and then briefly discuss
a range of methods, both theoretical and observational, that we are
using to advance the modelling. <P />This study uses observational
data from from HST, VLT, AAT, Kepler, and supercomputing resources in
Australia provided by the National Computational Infrastructure (NCI)
and Pawsey Supercomputing Centre.
---------------------------------------------------------
Title: Nominal Values for Selected Solar and Planetary Quantities:
IAU 2015 Resolution B3
Authors: Prša, Andrej; Harmanec, Petr; Torres, Guillermo; Mamajek,
Eric; Asplund, Martin; Capitaine, Nicole; Christensen-Dalsgaard,
Jørgen; Depagne, Éric; Haberreiter, Margit; Hekker, Saskia; Hilton,
James; Kopp, Greg; Kostov, Veselin; Kurtz, Donald W.; Laskar, Jacques;
Mason, Brian D.; Milone, Eugene F.; Montgomery, Michele; Richards,
Mercedes; Schmutz, Werner; Schou, Jesper; Stewart, Susan G.
2016AJ....152...41P Altcode: 2016arXiv160509788P
In this brief communication we provide the rationale for and the
outcome of the International Astronomical Union (IAU) resolution
vote at the XXIXth General Assembly in Honolulu, Hawaii, in 2015,
on recommended nominal conversion constants for selected solar and
planetary properties. The problem addressed by the resolution is a lack
of established conversion constants between solar and planetary values
and SI units: a missing standard has caused a proliferation of solar
values (e.g., solar radius, solar irradiance, solar luminosity, solar
effective temperature, and solar mass parameter) in the literature,
with cited solar values typically based on best estimates at the time
of paper writing. As precision of observations increases, a set of
consistent values becomes increasingly important. To address this, an
IAU Working Group on Nominal Units for Stellar and Planetary Astronomy
formed in 2011, uniting experts from the solar, stellar, planetary,
exoplanetary, and fundamental astronomy, as well as from general
standards fields to converge on optimal values for nominal conversion
constants. The effort resulted in the IAU 2015 Resolution B3, passed at
the IAU General Assembly by a large majority. The resolution recommends
the use of nominal solar and planetary values, which are by definition
exact and are expressed in SI units. These nominal values should be
understood as conversion factors only, not as the true solar/planetary
properties or current best estimates. Authors and journal editors are
urged to join in using the standard values set forth by this resolution
in future work and publications to help minimize further confusion.
---------------------------------------------------------
Title: On the uncertain nature of the core of α Cen A
Authors: Bazot, M.; Christensen-Dalsgaard, J.; Gizon, L.; Benomar, O.
2016MNRAS.460.1254B Altcode: 2016MNRAS.tmp..725B; 2016arXiv160307583B
High-quality astrometric, spectroscopic, interferometric and,
importantly, asteroseismic observations are available for α Cen A,
which is the closest binary star system to earth. Taking all these
constraints into account, we study the internal structure of the star
by means of theoretical modelling. Using the Aarhus STellar Evolution
Code (ASTEC) and the tools of Computational Bayesian Statistics, in
particular a Markov chain Monte Carlo algorithm, we perform statistical
inferences for the physical characteristics of the star. We find that
α Cen A has a probability of approximately 40 per cent of having
a convective core. This probability drops to few per cent if one
considers reduced rates for the <SUP>14</SUP>N(p,γ)<SUP>15</SUP>O
reaction. These convective cores have fractional radii less than 8 per
cent when overshoot is neglected. Including overshooting also leads
to the possibility of a convective core mostly sustained by the ppII
chain energy output. We finally show that roughly 30 per cent of the
stellar models describing α Cen A are in the subgiant regime.
---------------------------------------------------------
Title: SpaceInn hare-and-hounds exercise: Estimation of stellar
properties using space-based asteroseismic data
Authors: Reese, D. R.; Chaplin, W. J.; Davies, G. R.;
Miglio, A.; Antia, H. M.; Ball, W. H.; Basu, S.; Buldgen, G.;
Christensen-Dalsgaard, J.; Coelho, H. R.; Hekker, S.; Houdek, G.;
Lebreton, Y.; Mazumdar, A.; Metcalfe, T. S.; Silva Aguirre, V.;
Stello, D.; Verma, K.
2016A&A...592A..14R Altcode: 2016arXiv160408404R
Context. Detailed oscillation spectra comprising individual frequencies
for numerous solar-type stars and red giants are either currently
available, e.g. courtesy of the CoRoT, Kepler, and K2 missions, or
will become available with the upcoming NASA TESS and ESA PLATO 2.0
missions. The data can lead to a precise characterisation of these
stars thereby improving our understanding of stellar evolution,
exoplanetary systems, and the history of our galaxy. <BR /> Aims:
Our goal is to test and compare different methods for obtaining
stellar properties from oscillation frequencies and spectroscopic
constraints. Specifically, we would like to evaluate the accuracy of
the results and reliability of the associated error bars, and to see
where there is room for improvement. <BR /> Methods: In the context
of the SpaceInn network, we carried out a hare-and-hounds exercise
in which one group, the hares, simulated observations of oscillation
spectra for a set of ten artificial solar-type stars, and a number of
hounds applied various methods for characterising these stars based on
the data produced by the hares. Most of the hounds fell into two main
groups. The first group used forward modelling (I.e. applied various
search/optimisation algorithms in a stellar parameter space) whereas
the second group relied on acoustic glitch signatures. <BR /> Results:
Results based on the forward modelling approach were accurate to 1.5%
(radius), 3.9% (mass), 23% (age), 1.5% (surface gravity), and 1.8% (mean
density), as based on the root mean square difference. Individual hounds
reached different degrees of accuracy, some of which were substantially
better than the above average values. For the two 1M<SUB>⊙</SUB>
stellar targets, the accuracy on the age is better than 10% thereby
satisfying the requirements for the PLATO 2.0 mission. High stellar
masses and atomic diffusion (which in our models does not include
the effects of radiative accelerations) proved to be sources of
difficulty. The average accuracies for the acoustic radii of the base
of the convection zone, the He II ionisation, and the Γ<SUB>1</SUB>
peak located between the two He ionisation zones were 17%, 2.4%, and
1.9%, respectively. The results from the forward modelling were on
average more accurate than those from the glitch fitting analysis as
the latter seemed to be affected by aliasing problems for some of the
targets. <BR /> Conclusions: Our study indicates that forward modelling
is the most accurate way of interpreting the pulsation spectra of
solar-type stars. However, given its model-dependent nature, this
method needs to be complemented by model-independent results from,
e.g. glitch analysis. Furthermore, our results indicate that global
rather than local optimisation algorithms should be used in order to
obtain robust error bars.
---------------------------------------------------------
Title: The Transiting Exoplanet Survey Satellite
Authors: Ricker, G. R.; Vanderspek, R.; Winn, J.; Seager,
S.; Berta-Thompson, Z.; Levine, A.; Villasenor, J.; Latham, D.;
Charbonneau, D.; Holman, M.; Johnson, J.; Sasselov, D.; Szentgyorgyi,
A.; Torres, G.; Bakos, G.; Brown, T.; Christensen-Dalsgaard, J.;
Kjeldsen, H.; Clampin, M.; Rinehart, S.; Deming, D.; Doty, J.; Dunham,
E.; Ida, S.; Kawai, N.; Sato, B.; Jenkins, J.; Lissauer, J.; Jernigan,
G.; Kaltenegger, L.; Laughlin, G.; Lin, D.; McCullough, P.; Narita,
N.; Pepper, J.; Stassun, K.; Udry, S.
2016SPIE.9904E..2BR Altcode:
No abstract at ADS
---------------------------------------------------------
Title: VizieR Online Data Catalog: Surface gravity for 220 Kepler
stars (Campante+, 2014)
Authors: Campante, T. L.; Chaplin, W. J.; Lund, M. N.; Huber, D.;
Hekker, S.; Garcia, R. A.; Corsaro, E.; Handberg, R.; Miglio, A.;
Arentoft, T.; Basu, S.; Bedding, T. R.; Christensen-Dalsgaard, J.;
Davies, G. R.; Elsworth, Y. P.; Gilliland, R. L.; Karoff, C.; Kawaler,
S. D.; Kjeldsen, H.; Lundkvist, M.; Metcalfe, T. S.; Silva Aguirre,
V.; Stello, D.
2016yCat..17830123C Altcode:
We propose lower-limit surface gravity estimates for Kepler solar-type
planet-candidate host stars with no detected oscillations, as given
in Table4. <P />(1 data file).
---------------------------------------------------------
Title: Testing the asymptotic relation for period spacings from
mixed modes of red giants observed with the Kepler mission
Authors: Buysschaert, B.; Beck, P. G.; Corsaro, E.;
Christensen-Dalsgaard, J.; Aerts, C.; Arentoft, T.; Kjeldsen, H.;
García, R. A.; Silva Aguirre, V.; Degroote, P.
2016A&A...588A..82B Altcode: 2016arXiv160202716B
Context. Dipole mixed pulsation modes of consecutive radial order
have been detected for thousands of low-mass red-giant stars with the
NASA space telescope Kepler. These modes have the potential to reveal
information on the physics of the deep stellar interior. <BR /> Aims:
Different methods have been proposed to derive an observed value for
the gravity-mode period spacing, the most prominent one relying on
a relation derived from asymptotic pulsation theory applied to the
gravity-mode character of the mixed modes. Our aim is to compare
results based on this asymptotic relation with those derived from an
empirical approach for three pulsating red-giant stars. <BR /> Methods:
We developed a data-driven method to perform frequency extraction and
mode identification. Next, we used the identified dipole mixed modes
to determine the gravity-mode period spacing by means of an empirical
method and by means of the asymptotic relation. In our methodology we
consider the phase offset, ɛ<SUB>g</SUB>, of the asymptotic relation
as a free parameter. <BR /> Results: Using the frequencies of the
identified dipole mixed modes for each star in the sample, we derived
a value for the gravity-mode period spacing using the two different
methods. These values differ by less than 5%. The average precision we
achieved for the period spacing derived from the asymptotic relation
is better than 1%, while that of our data-driven approach is 3%. <BR
/> Conclusions: Good agreement is found between values for the period
spacing derived from the asymptotic relation and from the empirical
method. The achieved uncertainties are small, but do not support the
ultra-high precision claimed in the literature. The precision from
our data-driven method is mostly affected by the differing number of
observed dipole mixed modes. For the asymptotic relation, the phase
offset, ɛ<SUB>g</SUB>, remains ill defined, but enables a more robust
analysis of both the asymptotic period spacing and the dimensionless
coupling factor. However, its estimation might still offer a valuable
observational diagnostic for future theoretical modeling.
---------------------------------------------------------
Title: Hot super-Earths stripped by their host stars
Authors: Lundkvist, M. S.; Kjeldsen, H.; Albrecht, S.; Davies, G. R.;
Basu, S.; Huber, D.; Justesen, A. B.; Karoff, C.; Silva Aguirre, V.;
van Eylen, V.; Vang, C.; Arentoft, T.; Barclay, T.; Bedding, T. R.;
Campante, T. L.; Chaplin, W. J.; Christensen-Dalsgaard, J.; Elsworth,
Y. P.; Gilliland, R. L.; Handberg, R.; Hekker, S.; Kawaler, S. D.;
Lund, M. N.; Metcalfe, T. S.; Miglio, A.; Rowe, J. F.; Stello, D.;
Tingley, B.; White, T. R.
2016NatCo...711201L Altcode: 2016arXiv160405220L
Simulations predict that hot super-Earth sized exoplanets can have their
envelopes stripped by photoevaporation, which would present itself as
a lack of these exoplanets. However, this absence in the exoplanet
population has escaped a firm detection. Here we demonstrate, using
asteroseismology on a sample of exoplanets and exoplanet candidates
observed during the Kepler mission that, while there is an abundance of
super-Earth sized exoplanets with low incident fluxes, none are found
with high incident fluxes. We do not find any exoplanets with radii
between 2.2 and 3.8 Earth radii with incident flux above 650 times
the incident flux on Earth. This gap in the population of exoplanets
is explained by evaporation of volatile elements and thus supports
the predictions. The confirmation of a hot-super-Earth desert caused
by evaporation will add an important constraint on simulations of
planetary systems, since they must be able to reproduce the dearth of
close-in super-Earths.
---------------------------------------------------------
Title: Spin-Orbit Alignment of Exoplanet Systems: Ensemble Analysis
Using Asteroseismology
Authors: Campante, T. L.; Lund, M. N.; Kuszlewicz, J. S.; Davies,
G. R.; Chaplin, W. J.; Albrecht, S.; Winn, J. N.; Bedding, T. R.;
Benomar, O.; Bossini, D.; Handberg, R.; Santos, A. R. G.; Van Eylen,
V.; Basu, S.; Christensen-Dalsgaard, J.; Elsworth, Y. P.; Hekker, S.;
Hirano, T.; Huber, D.; Karoff, C.; Kjeldsen, H.; Lundkvist, M. S.;
North, T. S. H.; Silva Aguirre, V.; Stello, D.; White, T. R.
2016ApJ...819...85C Altcode: 2016arXiv160106052C
The angle ψ between a planet’s orbital axis and the spin axis
of its parent star is an important diagnostic of planet formation,
migration, and tidal evolution. We seek empirical constraints on ψ by
measuring the stellar inclination I<SUB>s</SUB> via asteroseismology
for an ensemble of 25 solar-type hosts observed with NASA’s Kepler
satellite. Our results for I<SUB>s</SUB> are consistent with alignment
at the 2σ level for all stars in the sample, meaning that the
system surrounding the red-giant star Kepler-56 remains as the only
unambiguous misaligned multiple-planet system detected to date. The
availability of a measurement of the projected spin-orbit angle λ
for two of the systems allows us to estimate ψ. We find that the
orbit of the hot Jupiter HAT-P-7b is likely to be retrograde (\psi
=116\buildrel{\circ}\over{.} {4}<SUB>-14.7</SUB><SUP>+30.2</SUP>),
whereas that of Kepler-25c seems to be well aligned with
the stellar spin axis (\psi =12\buildrel{\circ}\over{.}
{6}<SUB>-11.0</SUB><SUP>+6.7</SUP>). While the latter result is
in apparent contradiction with a statement made previously in the
literature that the multi-transiting system Kepler-25 is misaligned,
we show that the results are consistent, given the large associated
uncertainties. Finally, we perform a hierarchical Bayesian analysis
based on the asteroseismic sample in order to recover the underlying
distribution of ψ. The ensemble analysis suggests that the directions
of the stellar spin and planetary orbital axes are correlated, as
conveyed by a tendency of the host stars to display large values
of inclination.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Fundamental parameters of Kepler
stars (Silva Aguirre+, 2015)
Authors: Silva Aguirre, V.; Davies, G. R.; Basu, S.;
Christensen-Dalsgaard, J.; Creevey, O.; Metcalfe, T. S.; Bedding,
T. R.; Casagrande, L.; Handberg, R.; Lund, M. N.; Nissen, P. E.;
Chaplin, W. J.; Huber, D.; Serenelli, A. M.; Stello, D.; van Eylen,
V.; Campante, T. L.; Elsworth, Y.; Gilliland, R. L.; Hekker, S.;
Karoff, C.; Kawaler, S. D.; Kjeldsen, H.; Lundkvist, M. S.
2016yCat..74522127S Altcode:
Our sample has been extracted from the 77 exoplanet host stars presented
in Huber et al. (2013, Cat. J/ApJ/767/127). <P />We have made use of the
full time-base of observations from the Kepler satellite to uniformly
determine precise fundamental stellar parameters, including ages,
for a sample of exoplanet host stars where high-quality asteroseismic
data were available. We devised a Bayesian procedure flexible in its
input and applied it to different grids of models to study systematics
from input physics and extract statistically robust properties for
all stars. <P />(4 data files).
---------------------------------------------------------
Title: Oscillation frequencies for 35 Kepler solar-type planet-hosting
stars using Bayesian techniques and machine learning
Authors: Davies, G. R.; Silva Aguirre, V.; Bedding, T. R.; Handberg,
R.; Lund, M. N.; Chaplin, W. J.; Huber, D.; White, T. R.; Benomar,
O.; Hekker, S.; Basu, S.; Campante, T. L.; Christensen-Dalsgaard, J.;
Elsworth, Y.; Karoff, C.; Kjeldsen, H.; Lundkvist, M. S.; Metcalfe,
T. S.; Stello, D.
2016MNRAS.456.2183D Altcode: 2015arXiv151102105D
Kepler has revolutionized our understanding of both exoplanets and their
host stars. Asteroseismology is a valuable tool in the characterization
of stars and Kepler is an excellent observing facility to perform
asteroseismology. Here we select a sample of 35 Kepler solar-type stars
which host transiting exoplanets (or planet candidates) with detected
solar-like oscillations. Using available Kepler short cadence data up
to Quarter 16 we create power spectra optimized for asteroseismology
of solar-type stars. We identify modes of oscillation and estimate
mode frequencies by `peak bagging' using a Bayesian Markov Chain Monte
Carlo framework. In addition, we expand the methodology of quality
assurance using a Bayesian unsupervised machine learning approach. We
report the measured frequencies of the modes of oscillation for all
35 stars and frequency ratios commonly used in detailed asteroseismic
modelling. Due to the high correlations associated with frequency
ratios we report the covariance matrix of all frequencies measured
and frequency ratios calculated. These frequencies, frequency ratios,
and covariance matrices can be used to obtain tight constraint on the
fundamental parameters of these planet-hosting stars.
---------------------------------------------------------
Title: Asteroseismology with solar-like oscillations
Authors: Christensen-Dalsgaard, J.
2016arXiv160206838C Altcode:
Almost 100 years ago Sir Arthur Eddington noted that the interiors
of stars were inaccessible to observations. The advent of helio- and
asteroseismology has completely changed this assessment. Helioseismology
has provided very detailed information about the interior structure and
dynamics of the Sun, highlighting remaining issues in our understanding
of the solar interior. In the last decade extensive observations of
stellar oscillations, in particular from space photometry, have provided
very detailed information about the global and internal properties of
stars. Here I provide an overview of these developments, including
the remarkable insight that has been obtained on the properties of
evolved stars.
---------------------------------------------------------
Title: The Kepler-454 System: A Small, Not-rocky Inner Planet,
a Jovian World, and a Distant Companion
Authors: Gettel, Sara; Charbonneau, David; Dressing, Courtney D.;
Buchhave, Lars A.; Dumusque, Xavier; Vanderburg, Andrew; Bonomo, Aldo
S.; Malavolta, Luca; Pepe, Francesco; Collier Cameron, Andrew; Latham,
David W.; Udry, Stéphane; Marcy, Geoffrey W.; Isaacson, Howard;
Howard, Andrew W.; Davies, Guy R.; Silva Aguirre, Victor; Kjeldsen,
Hans; Bedding, Timothy R.; Lopez, Eric; Affer, Laura; Cosentino,
Rosario; Figueira, Pedro; Fiorenzano, Aldo F. M.; Harutyunyan, Avet;
Johnson, John Asher; Lopez-Morales, Mercedes; Lovis, Christophe;
Mayor, Michel; Micela, Giusi; Molinari, Emilio; Motalebi, Fatemeh;
Phillips, David F.; Piotto, Giampaolo; Queloz, Didier; Rice, Ken;
Sasselov, Dimitar; Ségransan, Damien; Sozzetti, Alessandro; Watson,
Chris; Basu, Sarbani; Campante, Tiago L.; Christensen-Dalsgaard,
Jørgen; Kawaler, Steven D.; Metcalfe, Travis S.; Handberg, Rasmus;
Lund, Mikkel N.; Lundkvist, Mia S.; Huber, Daniel; Chaplin, William J.
2016ApJ...816...95G Altcode: 2015arXiv151109097G
Kepler-454 (KOI-273) is a relatively bright (V = 11.69 mag), Sun-like
star that hosts a transiting planet candidate in a 10.6 day orbit. From
spectroscopy, we estimate the stellar temperature to be 5687 ± 50
K, its metallicity to be [m/H] = 0.32 ± 0.08, and the projected
rotational velocity to be v sin I < 2.4 km s<SUP>-1</SUP>. We
combine these values with a study of the asteroseismic frequencies
from short cadence Kepler data to estimate the stellar mass to
be {1.028}<SUB>-0.03</SUB><SUP>+0.04</SUP>{M}<SUB>⊙ </SUB>,
the radius to be 1.066 ± 0.012 R<SUB>⊙</SUB>, and the age to be
{5.25}<SUB>-1.39</SUB><SUP>+1.41</SUP> Gyr. We estimate the radius
of the 10.6 day planet as 2.37 ± 0.13 R<SUB>⊕</SUB>. Using 63
radial velocity observations obtained with the HARPS-N spectrograph
on the Telescopio Nazionale Galileo and 36 observations made with
the HIRES spectrograph at the Keck Observatory, we measure the mass
of this planet to be 6.8 ± 1.4 M<SUB>⊕</SUB>. We also detect two
additional non-transiting companions, a planet with a minimum mass
of 4.46 ± 0.12 M<SUB>J</SUB> in a nearly circular 524 day orbit
and a massive companion with a period >10 years and mass >12.1
M<SUB>J</SUB>. The 12 exoplanets with radii <2.7 R<SUB>⊕</SUB>
and precise mass measurements appear to fall into two populations, with
those <1.6 R<SUB>⊕</SUB> following an Earth-like composition curve
and larger planets requiring a significant fraction of volatiles. With
a density of 2.76 ± 0.73 g cm<SUP>-3</SUP>, Kepler-454b lies near
the mass transition between these two populations and requires the
presence of volatiles and/or H/He gas.
---------------------------------------------------------
Title: Internal Rotation of the Red-giant Star KIC 4448777 by Means
of Asteroseismic Inversion
Authors: Di Mauro, M. P.; Ventura, R.; Cardini, D.; Stello, D.;
Christensen-Dalsgaard, J.; Dziembowski, W. A.; Paternò, L.; Beck,
P. G.; Bloemen, S.; Davies, G. R.; De Smedt, K.; Elsworth, Y.; García,
R. A.; Hekker, S.; Mosser, B.; Tkachenko, A.
2016ApJ...817...65D Altcode: 2015arXiv151106160D
We study the dynamics of the stellar interior of the early red-giant
star KIC 4448777 by asteroseismic inversion of 14 splittings of
the dipole mixed modes obtained from Kepler observations. In order
to overcome the complexity of the oscillation pattern typical of
red-giant stars, we present a procedure to extract the rotational
splittings from the power spectrum. We find not only that the core
rotates from a minimum of 8 to a maximum of 17 times faster than the
surface, confirming previous inversion results generated for other
red giants (Deheuvels et al.), but we also estimate the variation of
the angular velocity within the helium core with a spatial resolution
of 0.001R and verify the hypothesis of a sharp discontinuity in the
inner stellar rotation. The results show that the entire core rotates
rigidly and provide evidence for an angular velocity gradient around
the base of the hydrogen-burning shell; however, we do not succeed in
characterizing the rotational slope, due to the intrinsic limits of
the applied techniques. The angular velocity, from the edge of the
core, appears to decrease with increasing distance from the center,
reaching an average value in the convective envelope of 68 ± 22
nHz. We conclude that a set of data that includes only dipolar modes
is sufficient to infer quite accurately the rotation of a red giant
not only in the dense core but also, with a lower level of confidence,
in part of the radiative region and in the convective envelope.
---------------------------------------------------------
Title: Asteroseismology of Exoplanet-Host Stars in the TESS Era
Authors: Campante, Tiago L.; Schofield, Mathew; Chaplin, William J.;
Huber, Daniel; Christensen-Dalsgaard, Jørgen; Kjeldsen, Hans; Latham,
David W.; Ricker, George R.; Winn, Joshua
2015ESS.....350303C Altcode:
New insights on stellar evolution and stellar interiors physics are
being made possible by asteroseismology, the study of stars by the
observation of their natural, resonant oscillations. Throughout the
duration of the Kepler mission, asteroseismology has also played
an important role in the characterization of host stars and their
planetary systems. Examples include the precise estimation of the
fundamental properties of stellar hosts, the obliquity determination
of planetary systems, or the orbital eccentricity determination via
asterodensity profiling. The Transiting Exoplanet Survey Satellite
(TESS) will perform a wide-field survey for planets that transit bright
host stars. Its excellent photometric precision and long intervals of
uninterrupted observations will enable asteroseismology of solar-type
stars and their evolved counterparts. Based on existing all-sky
simulations of the stellar and planetary populations, we investigate
the asteroseismic yield of the mission, placing particular emphasis
on the yield of exoplanet-host stars for which we expect to detect
solar-like oscillations. This is done both for the cohort of target
stars (observed at a 2-min cadence), which will mainly involve low-mass
main-sequence hosts, as well as for the cohort of “full-frame image”
stars (observed at a 30-min cadence). The latter cohort offers the
exciting prospect of conducting asteroseismology on a significant
number of evolved hosts. Also, the brightest solar-type hosts with
asteroseismology will become some of the best characterized planetary
systems known to date. Finally, we discuss the impact of the detected
oscillations on the accuracy/precision of the derived properties of
the host stars and their planetary systems.
---------------------------------------------------------
Title: IAU 2015 Resolution B2 on Recommended Zero Points for the
Absolute and Apparent Bolometric Magnitude Scales
Authors: Mamajek, E. E.; Torres, G.; Prsa, A.; Harmanec, P.;
Asplund, M.; Bennett, P. D.; Capitaine, N.; Christensen-Dalsgaard,
J.; Depagne, E.; Folkner, W. M.; Haberreiter, M.; Hekker, S.; Hilton,
J. L.; Kostov, V.; Kurtz, D. W.; Laskar, J.; Mason, B. D.; Milone,
E. F.; Montgomery, M. M.; Richards, M. T.; Schou, J.; Stewart, S. G.
2015arXiv151006262M Altcode:
The XXIXth IAU General Assembly in Honolulu adopted IAU 2015 Resolution
B2 on recommended zero points for the absolute and apparent bolometric
magnitude scales. The resolution was proposed by the IAU Inter-Division
A-G Working Group on Nominal Units for Stellar and Planetary
Astronomy after consulting with a broad spectrum of researchers from
the astronomical community. Resolution B2 resolves the long-standing
absence of an internationally-adopted zero point for the absolute and
apparent bolometric magnitude scales. Resolution B2 defines the zero
point of the absolute bolometric magnitude scale such that a radiation
source with $M_{\rm Bol}$ = 0 has luminosity L$_{\circ}$ = 3.0128e28
W. The zero point of the apparent bolometric magnitude scale ($m_{\rm
Bol}$ = 0) corresponds to irradiance $f_{\circ}$ = 2.518021002e-8
W/m$^2$. The zero points were chosen so that the nominal solar
luminosity (3.828e26 W) adopted by IAU 2015 Resolution B3 corresponds
approximately to $M_{\rm Bol}$(Sun) = 4.74, the value most commonly
adopted in recent literature. The nominal total solar irradiance (1361
W/m$^2$) adopted in IAU 2015 Resolution B3 corresponds approximately to
apparent bolometric magnitude $m_{\rm bol}$(Sun) = -26.832. Implicit
in the IAU 2015 Resolution B2 definition of the apparent bolometric
magnitude scale is an exact definition for the parsec (648000/$\pi$ au)
based on the IAU 2012 Resolution B2 definition of the astronomical unit.
---------------------------------------------------------
Title: Asteroseismology of Solar-Type Stars with K2: Detection of
Oscillations in C1 Data
Authors: Chaplin, W. J.; Lund, M. N.; Handberg, R.; Basu, S.;
Buchhave, L. A.; Campante, T. L.; Davies, G. R.; Huber, D.; Latham,
D. W.; Latham, C. A.; Serenelli, A.; Antia, H. M.; Appourchaux, T.;
Ball, W. H.; Benomar, O.; Casagrande, L.; Christensen-Dalsgaard, J.;
Coelho, H. R.; Creevey, O. L.; Elsworth, Y.; García, R. A.; Gaulme,
P.; Hekker, S.; Kallinger, T.; Karoff, C.; Kawaler, S. D.; Kjeldsen,
H.; Lundkvist, M. S.; Marcadon, F.; Mathur, S.; Miglio, A.; Mosser,
B.; Régulo, C.; Roxburgh, I. W.; Silva Aguirre, V.; Stello, D.;
Verma, K.; White, T. R.; Bedding, T. R.; Barclay, T.; Buzasi, D. L.;
Dehuevels, S.; Gizon, L.; Houdek, G.; Howell, S. B.; Salabert, D.;
Soderblom, D. R.
2015PASP..127.1038C Altcode: 2015arXiv150701827C
We present the first detections by the NASA K2 Mission of oscillations
in solar-type stars, using short-cadence data collected during
K2 Campaign\,1 (C1). We understand the asteroseismic detection
thresholds for C1-like levels of photometric performance, and we
can detect oscillations in subgiants having dominant oscillation
frequencies around $1000\,\rm \mu Hz$. Changes to the operation of the
fine-guidance sensors are expected to give significant improvements
in the high-frequency performance from C3 onwards. A reduction in the
excess high-frequency noise by a factor of two-and-a-half in amplitude
would bring main-sequence stars with dominant oscillation frequencies as
high as ${\simeq 2500}\,\rm \mu Hz$ into play as potential asteroseismic
targets for K2.
---------------------------------------------------------
Title: IAU 2015 Resolution B3 on Recommended Nominal Conversion
Constants for Selected Solar and Planetary Properties
Authors: Mamajek, E. E.; Prsa, A.; Torres, G.; Harmanec, P.;
Asplund, M.; Bennett, P. D.; Capitaine, N.; Christensen-Dalsgaard,
J.; Depagne, E.; Folkner, W. M.; Haberreiter, M.; Hekker, S.; Hilton,
J. L.; Kostov, V.; Kurtz, D. W.; Laskar, J.; Mason, B. D.; Milone,
E. F.; Montgomery, M. M.; Richards, M. T.; Schou, J.; Stewart, S. G.
2015arXiv151007674M Altcode:
Astronomers commonly quote the properties of celestial objects in
units of parameters for the Sun, Jupiter, or the Earth. The resolution
presented here was proposed by the IAU Inter-Division Working Group
on Nominal Units for Stellar and Planetary Astronomy and passed by the
XXIXth IAU General Assembly in Honolulu. IAU 2015 Resolution B3 adopts
a set of nominal solar, terrestrial, and jovian conversion constants
for stellar and (exo)planetary astronomy which are defined to be
exact SI values. While the nominal constants are based on current best
estimates (CBEs; which have uncertainties, are not secularly constant,
and are updated regularly using new observations), they should be
interpreted as standard values and not as CBEs. IAU 2015 Resolution
B3 adopts five solar conversion constants (nominal solar radius,
nominal total solar irradiance, nominal solar luminosity, nominal
solar effective temperature, and nominal solar mass parameter) and six
planetary conversion constants (nominal terrestrial equatorial radius,
nominal terrestrial polar radius, nominal jovian equatorial radius,
nominal jovian polar radius, nominal terrestrial mass parameter,
and nominal jovian mass parameter).
---------------------------------------------------------
Title: On the red-giant luminosity bump
Authors: Christensen-Dalsgaard, Jørgen
2015MNRAS.453..666C Altcode: 2015arXiv150705531C
The increase in luminosity as a star evolves on the red-giant branch
is interrupted briefly when the hydrogen-burning shell reaches the
vicinity of the composition discontinuity left behind from the first
convective dredge-up. The non-monotonic variation of luminosity causes
an accumulation of stars, known as the `bump', in the distribution of
stars in the colour-magnitude diagrams of stellar clusters, which has
substantial diagnostic potential. Here, I present numerical results
on this behaviour and discuss the physical reason for the luminosity
variation, with the goal of strengthening the understanding of origin
of the phenomenon and hence of its diagnostic potential.
---------------------------------------------------------
Title: Oscillations in g-mode period spacings in red giants as a
way to determine their state of evolution
Authors: Cunha, M. S.; Stello, D.; Avelino, P. P.;
Christensen-Dalsgaard, J.
2015EPJWC.10101014C Altcode:
In this work we consider the sensitivity of gravity-mode period spacings
to sharp changes in the inner structure of red giant stars, more
specifically in the buoyancy frequency inside the g-mode propagation
cavity. Based on a comparison between the solutions to the linear
pulsation equations in the Cowling approximation for pure g-modes with
results obtained with a full oscillation code we identify and correctly
interpret the signature of the above-mentioned sharp variations in
the period spacings. Two examples, of red giant models in different
evolutionary phases, are discussed. Detection of these signatures in
CoRoT, Kepler or future PLATO red-giant stars would pin down their
evolutionary state in an unprecedented way.
---------------------------------------------------------
Title: The treatment of mixing in core helium burning models -
I. Implications for asteroseismology
Authors: Constantino, Thomas; Campbell, Simon W.;
Christensen-Dalsgaard, Jørgen; Lattanzio, John C.; Stello, Dennis
2015MNRAS.452..123C Altcode: 2015arXiv150601209C
The detection of mixed oscillation modes offers a unique insight
into the internal structure of core helium burning (CHeB) stars. The
stellar structure during CHeB is very uncertain because the growth of
the convective core, and/or the development of a semiconvection zone,
is critically dependent on the treatment of convective boundaries. In
this study we calculate a suite of stellar structure models and their
non-radial pulsations to investigate why the predicted asymptotic g-mode
ℓ = 1 period spacing ΔΠ<SUB>1</SUB> is systematically lower than is
inferred from Kepler field stars. We find that only models with large
convective cores, such as those calculated with our newly proposed
`maximal-overshoot' scheme, can match the average ΔΠ<SUB>1</SUB>
reported. However, we also find another possible solution that
is related to the method used to determine ΔΠ<SUB>1</SUB>: mode
trapping can raise the observationally inferred ΔΠ<SUB>1</SUB> well
above its true value. Even after accounting for these two proposed
resolutions to the discrepancy in average ΔΠ<SUB>1</SUB>, models
still predict more CHeB stars with low ΔΠ<SUB>1</SUB> ( ≲ 270 s)
than are observed. We establish two possible remedies for this: (i)
there may be a difficulty in determining ΔΠ<SUB>1</SUB> for early
CHeB stars (when ΔΠ<SUB>1</SUB> is lowest) because of the effect that
the sharp composition profile at the hydrogen burning shell has on the
pulsations, or (ii) the mass of the helium core at the flash is higher
than predicted. Our conclusions highlight the need for the reporting
of selection effects in asteroseismic population studies in order to
safely use this information to constrain stellar evolution theory.
---------------------------------------------------------
Title: KOI-3158: The oldest known system of terrestrial-size planets
Authors: Campante, T. L.; Barclay, T.; Swift, J. J.; Huber, D.;
Adibekyan, V. Zh.; Cochran, W.; Burke, C. J.; Isaacson, H.; Quintana,
E. V.; Davies, G. R.; Silva Aguirre, V.; Ragozzine, D.; Riddle, R.;
Baranec, C.; Basu, S.; Chaplin, W. J.; Christensen-Dalsgaard, J.;
Metcalfe, T. S.; Bedding, T. R.; Handberg, R.; Stello, D.; Brewer,
J. M.; Hekker, S.; Karoff, C.; Kolbl, R.; Law, N. M.; Lundkvist, M.;
Miglio, A.; Rowe, J. F.; Santos, N. C.; Van Laerhoven, C.; Arentoft,
T.; Elsworth, Y. P.; Fischer, D. A.; Kawaler, S. D.; Kjeldsen, H.;
Lund, M. N.; Marcy, G. W.; Sousa, S. G.; Sozzetti, A.; White, T. R.
2015EPJWC.10102004C Altcode: 2015arXiv150107869C
The first discoveries of exoplanets around Sun-like stars have fueled
efforts to find ever smaller worlds evocative of Earth and other
terrestrial planets in the Solar System. While gas-giant planets
appear to form preferentially around metal-rich stars, small planets
(with radii less than four Earth radii) can form under a wide range of
metallicities. This implies that small, including Earth-size, planets
may have readily formed at earlier epochs in the Universe's history when
metals were far less abundant. We report Kepler spacecraft observations
of KOI-3158, a metal-poor Sun-like star from the old population of the
Galactic thick disk, which hosts five planets with sizes between Mercury
and Venus. We used asteroseismology to directly measure a precise age
of 11.2 ± 1.0 Gyr for the host star, indicating that KOI-3158 formed
when the Universe was less than 20 % of its current age and making
it the oldest known system of terrestrial-size planets. We thus show
that Earth-size planets have formed throughout most of the Universe's
13.8-billion-year history, providing scope for the existence of ancient
life in the Galaxy.
---------------------------------------------------------
Title: What asteroseismology can do for exoplanets
Authors: Van Eylen, Vincent; Lund, Mikkel N.; Silva Aguirre, Victor;
Arentoft, Torben; Kjeldsen, Hans; Albrecht, Simon; Chaplin, William
J.; Isaacson, Howard; Pedersen, May G.; Jessen-Hansen, Jens; Tingley,
Brandon; Christensen-Dalsgaard, Jørgen; Aerts, Conny; Campante,
Tiago L.; Bryson, Steve T.
2015EPJWC.10102005V Altcode: 2014arXiv1412.4848V
We describe three useful applications of asteroseismology in the
context of exoplanet science: (1) the detailed characterisation of
exoplanet host stars; (2) the measurement of stellar inclinations; and
(3) the determination of orbital eccentricity from transit duration
making use of asteroseismic stellar densities. We do so using the
example system Kepler-410 [1]. This is one of the brightest (V = 9.4)
Kepler exoplanet host stars, containing a small (2.8 R<SUB>⊕</SUB>)
transiting planet in a long orbit (17.8 days), and one or more
additional non-transiting planets as indicated by transit timing
variations. The validation of Kepler-410 (KOI-42) was complicated due
to the presence of a companion star, and the planetary nature of the
system was confirmed after analyzing a Spitzer transit observation as
well as ground-based follow-up observations.
---------------------------------------------------------
Title: The Internal Rotation Profile of the B-type Star KIC 10526294
from Frequency Inversion of its Dipole Gravity Modes
Authors: Triana, S. A.; Moravveji, E.; Pápics, P. I.; Aerts, C.;
Kawaler, S. D.; Christensen-Dalsgaard, J.
2015ApJ...810...16T Altcode: 2015arXiv150704574T; 2015arXiv150704574A
The internal angular momentum distribution of a star is the key to
determining its evolution. Fortunately, stellar internal rotation can
be probed through studies of rotationally split nonradial oscillation
modes. In particular, the detection of nonradial gravity modes (g
modes) in massive young stars has recently become feasible thanks to
the Kepler space mission. Our goal is to derive the internal rotation
profile of the Kepler B8V star KIC 10526294 through asteroseismology. We
interpret the observed rotational splittings of its dipole g modes
using four different approaches based on the best seismic models of
the star and their rotational kernels. We show that these kernels
can resolve differential rotation within the radiative envelope if a
smooth rotational profile is assumed and if the observational errors
are small. Based on Kepler data, we find that the rotation rate near
the core-envelope boundary is well constrained to 163 ± 89 nHz. The
seismic data are consistent with rigid rotation but a profile with
counter-rotation within the envelope has a statistical advantage over
constant rotation. Our study should be repeated for other massive stars
with a variety of stellar parameters in order to determine the physical
conditions that control the internal rotation profile of young massive
stars, with the aim of improving the input physics of their models.
---------------------------------------------------------
Title: The Surface of Stellar Models - Now with more 3D simulations!
Authors: Trampedach, Regner; Christensen-Dalsgaard, Jørgen; Asplund,
Martin; Stein, Robert F.; Nordlund, Åke
2015EPJWC.10106064T Altcode:
We have constructed a grid of 3D hydrodynamic simulations of deep
convective and line-blanketed atmospheres. We have developed a
new consistent method for computing and employing T(τ) relations
from these simulations, as surface boundary conditions for 1D
stellar structure models. These 1D models have, in turn, had their
mixing-length, α, calibrated against the averaged structure of
each of the simulations. Both α and T(τ) vary significantly with
T<SUB>eff</SUB> and log g.
---------------------------------------------------------
Title: Ages and fundamental properties of Kepler exoplanet host
stars from asteroseismology
Authors: Silva Aguirre, V.; Davies, G. R.; Basu, S.;
Christensen-Dalsgaard, J.; Creevey, O.; Metcalfe, T. S.; Bedding,
T. R.; Casagrande, L.; Handberg, R.; Lund, M. N.; Nissen, P. E.;
Chaplin, W. J.; Huber, D.; Serenelli, A. M.; Stello, D.; Van Eylen,
V.; Campante, T. L.; Elsworth, Y.; Gilliland, R. L.; Hekker, S.;
Karoff, C.; Kawaler, S. D.; Kjeldsen, H.; Lundkvist, M. S.
2015MNRAS.452.2127S Altcode: 2015arXiv150407992S
We present a study of 33 Kepler planet-candidate host stars for which
asteroseismic observations have sufficiently high signal-to-noise
ratio to allow extraction of individual pulsation frequencies. We
implement a new Bayesian scheme that is flexible in its input to process
individual oscillation frequencies, combinations of them, and average
asteroseismic parameters, and derive robust fundamental properties for
these targets. Applying this scheme to grids of evolutionary models
yields stellar properties with median statistical uncertainties
of 1.2 per cent (radius), 1.7 per cent (density), 3.3 per cent
(mass), 4.4 per cent (distance), and 14 per cent (age), making this
the exoplanet host-star sample with the most precise and uniformly
determined fundamental parameters to date. We assess the systematics
from changes in the solar abundances and mixing-length parameter,
showing that they are smaller than the statistical errors. We also
determine the stellar properties with three other fitting algorithms
and explore the systematics arising from using different evolution
and pulsation codes, resulting in 1 per cent in density and radius,
and 2 per cent and 7 per cent in mass and age, respectively. We
confirm previous findings of the initial helium abundance being a
source of systematics comparable to our statistical uncertainties,
and discuss future prospects for constraining this parameter by
combining asteroseismology and data from space missions. Finally, we
compare our derived properties with those obtained using the global
average asteroseismic observables along with effective temperature and
metallicity, finding excellent level of agreement. Owing to selection
effects, our results show that the majority of the high signal-to-noise
ratio asteroseismic Kepler host stars are older than the Sun.
---------------------------------------------------------
Title: Division II: Commission 12: Solar Radiation and Structure
Authors: Kosovichev, Alexander; Cauzzi, Gianna; Martinez Pillet,
Valentin; Asplund, Martin; Brandenburg, Axel; Chou, Dean-Yi;
Christensen-Dalsgaard, Jorgen; Gan, Weiqun; Kuznetsov, Vladimir D.;
Rovira, Marta G.; Shchukina, Nataliya; Venkatakrishnan, P.
2015IAUTB..28..109K Altcode:
The President of C12, Alexander Kosovichev, presented the status of
the Commission and its working Group(s). Primary activities included
organization of international meetings (IAU Symposia, Special Sessions
and Joint Discussion); review and support of proposals for IAU sponsored
meetings; organization of working groups on the Commission topics
to promote the international cooperation; preparation of triennial
report on the organizational and science activities of Commission
members. Commission 12 broadly encompasses topics of solar research
which include studies of the Sun's internal structure, composition,
dynamics and magnetism (through helioseismology and other techniques),
studies of the quiet photosphere, chromosphere and corona, and also
research of the mechanisms of solar radiation, and its variability on
various time scales. Some overlap with topics covered by Commission
10 Solar Activity is unavoidable, and many activities are sponsored
jointly by these two commissions. The Commission website can be found
at http://sun.stanford.edu/IAU-Com12/, with information about related
IAU Symposiums and activities, and links to appropriate web sites.
---------------------------------------------------------
Title: The Stellar Observations Network Group - first results
Authors: Antoci, Victoria; Grundahl, Frank; Christensen-Dalsgaard,
Joergen; Kjeldsen, Hans
2015IAUGA..2258061A Altcode:
SONG - the Stellar Observations Network Group is a Danish-led project
set to design and build a global network of 1-m telescopes to carry
out detailed studies of solar-like stars using asteroseismology and
to discover and characterise exo-planets and their star system. Here
we present more than 100 nights of high-precision radial velocity
measurements from 2014 of the subgiant mu Herculis. Preliminary
analyses of the largest ground-based data set ever obtained for
such as star clearly show the detection of stochastically excited
pressure modes. The high quality of our data allows unique extraction
of individual modes over many orders in the frequency spectrum,
leading to studies of rotation, convection, near-surface effects,
core structure using mixed modes and stellar activity.
---------------------------------------------------------
Title: From the Sun to the distant stars, and back: Future research
directions
Authors: Christensen-Dalsgaard, J.
2015exse.book..276C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Helioseismology: Observations and space missions
Authors: Pallé, P. L.; Appourchaux, T.; Christensen-Dalsgaard, J.;
Garcxía, I. A.
2015exse.book...25P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A bright outlook for helio- and asteroseismology
Authors: Christensen-Dalsgaard, J.
2015exse.book....5C Altcode:
No abstract at ADS
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Title: Structural Glitches near the Cores of Red Giants Revealed by
Oscillations in g-mode Period Spacings from Stellar Models
Authors: Cunha, M. S.; Stello, D.; Avelino, P. P.;
Christensen-Dalsgaard, J.; Townsend, R. H. D.
2015ApJ...805..127C Altcode: 2015arXiv150309085C
With recent advances in asteroseismology it is now possible to peer
into the cores of red giants, potentially providing a way to study
processes such as nuclear burning and mixing through their imprint as
sharp structural variations—glitches—in the stellar cores. Here we
show how such core glitches can affect the oscillations we observe in
red giants. We derive an analytical expression describing the expected
frequency pattern in the presence of a glitch. This formulation also
accounts for the coupling between acoustic and gravity waves. From
an extensive set of canonical stellar models we find glitch-induced
variation in the period spacing and inertia of non-radial modes
during several phases of red giant evolution. Significant changes are
seen in the appearance of mode amplitude and frequency patterns in
asteroseismic diagrams such as the power spectrum and the échelle
diagram. Interestingly, along the red giant branch glitch-induced
variation occurs only at the luminosity bump, potentially
providing a direct seismic indicator of stars in that particular
evolution stage. Similarly, we find the variation at only certain
post-helium-ignition evolution stages, namely, in the early phases
of helium core burning and at the beginning of helium shell burning,
signifying the asymptotic giant branch bump. Based on our results,
we note that assuming stars to be glitch-free, while they are not,
can result in an incorrect estimate of the period spacing. We further
note that including diffusion and mixing beyond classical Schwarzschild
could affect the characteristics of the glitches, potentially providing
a way to study these physical processes.
---------------------------------------------------------
Title: Kepler-432: A Red Giant Interacting with One of its Two
Long-period Giant Planets
Authors: Quinn, Samuel N.; White, Timothy. R.; Latham, David W.;
Chaplin, William J.; Handberg, Rasmus; Huber, Daniel; Kipping, David
M.; Payne, Matthew J.; Jiang, Chen; Silva Aguirre, Victor; Stello,
Dennis; Sliski, David H.; Ciardi, David R.; Buchhave, Lars A.; Bedding,
Timothy R.; Davies, Guy R.; Hekker, Saskia; Kjeldsen, Hans; Kuszlewicz,
James S.; Everett, Mark E.; Howell, Steve B.; Basu, Sarbani; Campante,
Tiago L.; Christensen-Dalsgaard, Jørgen; Elsworth, Yvonne P.; Karoff,
Christoffer; Kawaler, Steven D.; Lund, Mikkel N.; Lundkvist, Mia;
Esquerdo, Gilbert A.; Calkins, Michael L.; Berlind, Perry
2015ApJ...803...49Q Altcode: 2014arXiv1411.4666Q
We report the discovery of Kepler-432b, a giant planet
({{M}<SUB>b</SUB>}=5.41<SUB>-0.18</SUB><SUP>+0.32</SUP>
{{M}<SUB>Jup</SUB>},
{{R}<SUB>b</SUB>}=1.145<SUB>-0.039</SUB><SUP>+0.036</SUP>
{{R}<SUB>Jup</SUB>}) transiting an evolved star ({{M}<SUB>\star
</SUB>}=1.32<SUB>-0.07</SUB><SUP>+0.10</SUP> {{M}<SUB>⊙
</SUB>},{{R}<SUB>\star </SUB>}=4.06<SUB>-0.08</SUB><SUP>+0.12</SUP>
{{R}<SUB>⊙ </SUB>}) with an orbital period of
{{P}<SUB>b</SUB>}=52.501129<SUB>-0.000053</SUB><SUP>+0.000067</SUP>
days. Radial velocities (RVs) reveal that Kepler-432b
orbits its parent star with an eccentricity of
e=0.5134<SUB>-0.0089</SUB><SUP>+0.0098</SUP>, which we
also measure independently with asterodensity profiling (AP;
e=0.507<SUB>-0.114</SUB><SUP>+0.039</SUP>), thereby confirming the
validity of AP on this particular evolved star. The well-determined
planetary properties and unusually large mass also make this planet
an important benchmark for theoretical models of super-Jupiter
formation. Long-term RV monitoring detected the presence of a
non-transiting outer planet (Kepler-432c; {{M}<SUB>c</SUB>}sin
{{i}<SUB>c</SUB>}=2.43<SUB>-0.24</SUB><SUP>+0.22</SUP>
{{M}<SUB>Jup</SUB>},
{{P}<SUB>c</SUB>}=406.2<SUB>-2.5</SUB><SUP>+3.9</SUP>
days), and adaptive optics imaging revealed a nearby
(0\buildrel{\prime\prime}\over{.} 87), faint companion (Kepler-432B)
that is a physically bound M dwarf. The host star exhibits high
signal-to-noise ratio asteroseismic oscillations, which enable precise
measurements of the stellar mass, radius, and age. Analysis of the
rotational splitting of the oscillation modes additionally reveals
the stellar spin axis to be nearly edge-on, which suggests that the
stellar spin is likely well aligned with the orbit of the transiting
planet. Despite its long period, the obliquity of the 52.5 day orbit may
have been shaped by star-planet interaction in a manner similar to hot
Jupiter systems, and we present observational and theoretical evidence
to support this scenario. Finally, as a short-period outlier among giant
planets orbiting giant stars, study of Kepler-432b may help explain the
distribution of massive planets orbiting giant stars interior to 1 AU.
---------------------------------------------------------
Title: Song
Authors: Christensen-Dalsgaard, Jorgen
2015mwss.confE..44C Altcode:
No abstract at ADS
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Title: An Ancient Extrasolar System with Five Sub-Earth-size Planets
Authors: Campante, T. L.; Barclay, T.; Swift, J. J.; Huber, D.;
Adibekyan, V. Zh.; Cochran, W.; Burke, C. J.; Isaacson, H.; Quintana,
E. V.; Davies, G. R.; Silva Aguirre, V.; Ragozzine, D.; Riddle, R.;
Baranec, C.; Basu, S.; Chaplin, W. J.; Christensen-Dalsgaard, J.;
Metcalfe, T. S.; Bedding, T. R.; Handberg, R.; Stello, D.; Brewer,
J. M.; Hekker, S.; Karoff, C.; Kolbl, R.; Law, N. M.; Lundkvist, M.;
Miglio, A.; Rowe, J. F.; Santos, N. C.; Van Laerhoven, C.; Arentoft,
T.; Elsworth, Y. P.; Fischer, D. A.; Kawaler, S. D.; Kjeldsen, H.;
Lund, M. N.; Marcy, G. W.; Sousa, S. G.; Sozzetti, A.; White, T. R.
2015ApJ...799..170C Altcode: 2015arXiv150106227C
The chemical composition of stars hosting small exoplanets (with radii
less than four Earth radii) appears to be more diverse than that of
gas-giant hosts, which tend to be metal-rich. This implies that small,
including Earth-size, planets may have readily formed at earlier
epochs in the universe's history when metals were more scarce. We
report Kepler spacecraft observations of Kepler-444, a metal-poor
Sun-like star from the old population of the Galactic thick disk and
the host to a compact system of five transiting planets with sizes
between those of Mercury and Venus. We validate this system as a true
five-planet system orbiting the target star and provide a detailed
characterization of its planetary and orbital parameters based on
an analysis of the transit photometry. Kepler-444 is the densest
star with detected solar-like oscillations. We use asteroseismology
to directly measure a precise age of 11.2 ± 1.0 Gyr for the host
star, indicating that Kepler-444 formed when the universe was less
than 20% of its current age and making it the oldest known system of
terrestrial-size planets. We thus show that Earth-size planets have
formed throughout most of the universe's 13.8 billion year history,
leaving open the possibility for the existence of ancient life in the
Galaxy. The age of Kepler-444 not only suggests that thick-disk stars
were among the hosts to the first Galactic planets, but may also help
to pinpoint the beginning of the era of planet formation.
---------------------------------------------------------
Title: The two-colour EMCCD instrument for the Danish 1.54 m telescope
and SONG
Authors: Skottfelt, J.; Bramich, D. M.; Hundertmark, M.; Jørgensen,
U. G.; Michaelsen, N.; Kjærgaard, P.; Southworth, J.; Sørensen,
A. N.; Andersen, M. F.; Andersen, M. I.; Christensen-Dalsgaard, J.;
Frandsen, S.; Grundahl, F.; Harpsøe, K. B. W.; Kjeldsen, H.; Pallé,
P. L.
2015A&A...574A..54S Altcode: 2014arXiv1411.7401S
We report on the implemented design of a two-colour instrument based
on electron-multiplying CCD (EMCCD) detectors. This instrument is
currently installed at the Danish 1.54 m telescope at ESO's La Silla
Observatory in Chile, and will be available at the SONG (Stellar
Observations Network Group) 1m telescope node at Tenerife and at other
SONG nodes as well. We present the software system for controlling the
two-colour instrument and calibrating the high frame-rate imaging data
delivered by the EMCCD cameras. An analysis of the performance of the
Two-Colour Instrument at the Danish telescope shows an improvement in
spatial resolution of up to a factor of two when doing shift-and-add
compared with conventional imaging, and the possibility of doing
high-precision photometry of EMCCD data in crowded fields. The Danish
telescope, which was commissioned in 1979, is limited by a triangular
coma at spatial resolutions below 0.5 arcsec, and better results will
thus be achieved at the near diffraction-limited optical system on
the SONG telescopes, where spatial resolutions close to 0.2 arcsec
have been achieved. Regular EMCCD operations have been running at the
Danish telescope for several years and produced a number of scientific
discoveries, including microlensing detected exoplanets, detecting
previously unknown variable stars in dense globular clusters, and
discovering two rings around the small asteroid-like object (10199)
Chariklo. <P />Based on data collected with the Danish 1.54m telescope
at ESO's La Silla Observatory.
---------------------------------------------------------
Title: Erratum: Sounding stellar cycles with Kepler - II. Ground-based
observations
Authors: Karoff, C.; Metcalfe, T. S.; Chaplin, W. J.; Frandsen, S.;
Grundahl, F.; Kjeldsen, H.; Christensen-Dalsgaard, J.; Nielsen, M. B.;
Frimann, S.; Thygesen, A. O.; Arentoft, T.; Amby, T. M.; Sousa, S. G.;
Buzasi, D. L.
2015MNRAS.446.1139K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Transiting Exoplanet Survey Satellite (TESS)
Authors: Ricker, George R.; Winn, Joshua N.; Vanderspek, Roland;
Latham, David W.; Bakos, Gáspár Á.; Bean, Jacob L.; Berta-Thompson,
Zachory K.; Brown, Timothy M.; Buchhave, Lars; Butler, Nathaniel
R.; Butler, R. Paul; Chaplin, William J.; Charbonneau, David;
Christensen-Dalsgaard, Jørgen; Clampin, Mark; Deming, Drake; Doty,
John; De Lee, Nathan; Dressing, Courtney; Dunham, Edward W.; Endl,
Michael; Fressin, Francois; Ge, Jian; Henning, Thomas; Holman, Matthew
J.; Howard, Andrew W.; Ida, Shigeru; Jenkins, Jon M.; Jernigan,
Garrett; Johnson, John Asher; Kaltenegger, Lisa; Kawai, Nobuyuki;
Kjeldsen, Hans; Laughlin, Gregory; Levine, Alan M.; Lin, Douglas;
Lissauer, Jack J.; MacQueen, Phillip; Marcy, Geoffrey; McCullough,
Peter R.; Morton, Timothy D.; Narita, Norio; Paegert, Martin; Palle,
Enric; Pepe, Francesco; Pepper, Joshua; Quirrenbach, Andreas; Rinehart,
Stephen A.; Sasselov, Dimitar; Sato, Bun'ei; Seager, Sara; Sozzetti,
Alessandro; Stassun, Keivan G.; Sullivan, Peter; Szentgyorgyi, Andrew;
Torres, Guillermo; Udry, Stephane; Villasenor, Joel
2015JATIS...1a4003R Altcode:
The Transiting Exoplanet Survey Satellite (TESS) will search for
planets transiting bright and nearby stars. TESS has been selected
by NASA for launch in 2017 as an Astrophysics Explorer mission. The
spacecraft will be placed into a highly elliptical 13.7-day orbit
around the Earth. During its 2-year mission, TESS will employ four
wide-field optical charge-coupled device cameras to monitor at least
200,000 main-sequence dwarf stars with I<SUB>C</SUB>≈4-13 for
temporary drops in brightness caused by planetary transits. Each
star will be observed for an interval ranging from 1 month to 1
year, depending mainly on the star's ecliptic latitude. The longest
observing intervals will be for stars near the ecliptic poles, which
are the optimal locations for follow-up observations with the James
Webb Space Telescope. Brightness measurements of preselected target
stars will be recorded every 2 min, and full frame images will be
recorded every 30 min. TESS stars will be 10 to 100 times brighter
than those surveyed by the pioneering Kepler mission. This will make
TESS planets easier to characterize with follow-up observations. TESS
is expected to find more than a thousand planets smaller than Neptune,
including dozens that are comparable in size to the Earth. Public data
releases will occur every 4 months, inviting immediate community-wide
efforts to study the new planets. The TESS legacy will be a catalog
of the nearest and brightest stars hosting transiting planets, which
will endure as highly favorable targets for detailed investigations.
---------------------------------------------------------
Title: Hardware and software for a robotic network of telescopes
- SONG
Authors: Andersen, M. F.; Grundahl, F.; Christensen-Dalsgaard, J.;
Frandsen, S.; Jørgensen, U. G.; Kjeldsen, H.; Pallé, P.; Skottfelt,
J.; Sørensen, A. N.; Weiss, E.
2014RMxAC..45...83A Altcode: 2019arXiv190108300A
SONG aims at setting up a network of small 1m telescopes around the
globe to observe stars uninterrupted throughout days, weeks and even
months. This paper describes the fundamental aspects for putting up
such a network and how we will operate each site as part of the full
network. The SONG observatories will be working autonomously and
automatic and can be fully controlled remotely.
---------------------------------------------------------
Title: Improvements to stellar structure models, based on a grid of 3D
convection simulations - II. Calibrating the mixing-length formulation
Authors: Trampedach, Regner; Stein, Robert F.; Christensen-Dalsgaard,
Jørgen; Nordlund, Åke; Asplund, Martin
2014MNRAS.445.4366T Altcode: 2014arXiv1410.1559T
We perform a calibration of the mixing length of convection in stellar
structure models against realistic 3D radiation-coupled hydrodynamics
simulations of convection in stellar surface layers, determining
the adiabat deep in convective stellar envelopes. The mixing-length
parameter α is calibrated by matching averages of the 3D simulations
to 1D stellar envelope models, ensuring identical atomic physics
in the two cases. This is done for a previously published grid of
solar-metallicity convection simulations, covering from 4200 to 6900 K
on the main sequence, and from 4300 to 5000 K for giants with log g =
2.2. Our calibration results in an α varying from 1.6 for the warmest
dwarf, which is just cool enough to admit a convective envelope, and
up to 2.05 for the coolest dwarfs in our grid. In between these is a
triangular plateau of α ∼ 1.76. The Sun is located on this plateau
and has seen little change during its evolution so far. When stars
ascend the giant branch, they largely do so along tracks of constant
α, with α decreasing with increasing mass.
---------------------------------------------------------
Title: On the asymptotic acoustic-mode phase in red giant stars and
its dependence on evolutionary state
Authors: Christensen-Dalsgaard, Jørgen; Silva Aguirre, Victor;
Elsworth, Yvonne; Hekker, Saskia
2014MNRAS.445.3685C Altcode: 2014arXiv1409.7949C
Asteroseismic investigations based on the wealth of data now available,
in particular from the CoRoT and Kepler missions, require a good
understanding of the relation between the observed quantities and the
properties of the underlying stellar structure. Kallinger et al. found a
relation between their determination of the asymptotic phase of radial
oscillations in evolved stars and the evolutionary state, separating
ascending-branch red giants from helium-burning stars in the `red
clump'. Here, we provide a detailed analysis of this relation, which is
found to derive from differences between these two classes of stars in
the thermodynamic state of the convective envelope. There is potential
for distinguishing red giants and clump stars based on the phase
determined from observations that are too short to allow distinction
based on determination of the period spacing for mixed modes. The
analysis of the phase may also point to a better understanding of the
potential for using the helium-ionization-induced acoustic glitch to
determine the helium abundance in the envelopes of these stars.
---------------------------------------------------------
Title: Verification of asymptotic relation for mixed modes in red
giant stars
Authors: Jiang, C.; Christensen-Dalsgaard, J.
2014MNRAS.444.3622J Altcode: 2014arXiv1406.1825J
High-precision space observations, such as made by the Kepler and CoRoT
missions, allow us to detect mixed modes for l = 1 modes in their
high signal-to-noise photometry data. By means of asteroseismology,
the inner structure of red giant (RG) stars is revealed for the first
time with the help of mixed modes. We analyse these mixed modes of
a 1.3 M<SUB>⊙</SUB> RG model theoretically from the approximate
asymptotic descriptions of oscillations. While fitting observed
frequencies with the eigenvalue condition for mixed modes, a good
estimate of period spacing and coupling strength is also acquired for
more evolved models. We show that the behaviour of the mode inertia
in a given mode varies dramatically when the coupling is strong. An
approximation of period spacings is also obtained from the asymptotic
dispersion relation, which provides a good estimate of the coupling
strength as well as period spacing when g-mode-like mixed modes are
sufficiently dense. By comparing the theoretical coupling strength
from the integral expression with the ones from fitting methods, we
confirmed that the theoretical asymptotic equation is problematic in
the evanescent region due to the potential singularities as well as
the use of the Cowling approximation.
---------------------------------------------------------
Title: The PLATO 2.0 mission
Authors: Rauer, H.; Catala, C.; Aerts, C.; Appourchaux, T.; Benz,
W.; Brandeker, A.; Christensen-Dalsgaard, J.; Deleuil, M.; Gizon,
L.; Goupil, M. -J.; Güdel, M.; Janot-Pacheco, E.; Mas-Hesse,
M.; Pagano, I.; Piotto, G.; Pollacco, D.; Santos, Ċ.; Smith, A.;
Suárez, J. -C.; Szabó, R.; Udry, S.; Adibekyan, V.; Alibert, Y.;
Almenara, J. -M.; Amaro-Seoane, P.; Eiff, M. Ammler-von; Asplund, M.;
Antonello, E.; Barnes, S.; Baudin, F.; Belkacem, K.; Bergemann, M.;
Bihain, G.; Birch, A. C.; Bonfils, X.; Boisse, I.; Bonomo, A. S.;
Borsa, F.; Brandão, I. M.; Brocato, E.; Brun, S.; Burleigh, M.;
Burston, R.; Cabrera, J.; Cassisi, S.; Chaplin, W.; Charpinet, S.;
Chiappini, C.; Church, R. P.; Csizmadia, Sz.; Cunha, M.; Damasso, M.;
Davies, M. B.; Deeg, H. J.; Díaz, R. F.; Dreizler, S.; Dreyer, C.;
Eggenberger, P.; Ehrenreich, D.; Eigmüller, P.; Erikson, A.; Farmer,
R.; Feltzing, S.; de Oliveira Fialho, F.; Figueira, P.; Forveille,
T.; Fridlund, M.; García, R. A.; Giommi, P.; Giuffrida, G.; Godolt,
M.; Gomes da Silva, J.; Granzer, T.; Grenfell, J. L.; Grotsch-Noels,
A.; Günther, E.; Haswell, C. A.; Hatzes, A. P.; Hébrard, G.; Hekker,
S.; Helled, R.; Heng, K.; Jenkins, J. M.; Johansen, A.; Khodachenko,
M. L.; Kislyakova, K. G.; Kley, W.; Kolb, U.; Krivova, N.; Kupka, F.;
Lammer, H.; Lanza, A. F.; Lebreton, Y.; Magrin, D.; Marcos-Arenal,
P.; Marrese, P. M.; Marques, J. P.; Martins, J.; Mathis, S.; Mathur,
S.; Messina, S.; Miglio, A.; Montalban, J.; Montalto, M.; Monteiro,
M. J. P. F. G.; Moradi, H.; Moravveji, E.; Mordasini, C.; Morel, T.;
Mortier, A.; Nascimbeni, V.; Nelson, R. P.; Nielsen, M. B.; Noack,
L.; Norton, A. J.; Ofir, A.; Oshagh, M.; Ouazzani, R. -M.; Pápics,
P.; Parro, V. C.; Petit, P.; Plez, B.; Poretti, E.; Quirrenbach, A.;
Ragazzoni, R.; Raimondo, G.; Rainer, M.; Reese, D. R.; Redmer, R.;
Reffert, S.; Rojas-Ayala, B.; Roxburgh, I. W.; Salmon, S.; Santerne,
A.; Schneider, J.; Schou, J.; Schuh, S.; Schunker, H.; Silva-Valio,
A.; Silvotti, R.; Skillen, I.; Snellen, I.; Sohl, F.; Sousa, S. G.;
Sozzetti, A.; Stello, D.; Strassmeier, K. G.; Švanda, M.; Szabó,
Gy. M.; Tkachenko, A.; Valencia, D.; Van Grootel, V.; Vauclair,
S. D.; Ventura, P.; Wagner, F. W.; Walton, N. A.; Weingrill, J.;
Werner, S. C.; Wheatley, P. J.; Zwintz, K.
2014ExA....38..249R Altcode: 2014ExA...tmp...41R; 2013arXiv1310.0696R
PLATO 2.0 has recently been selected for ESA's M3 launch opportunity
(2022/24). Providing accurate key planet parameters (radius, mass,
density and age) in statistical numbers, it addresses fundamental
questions such as: How do planetary systems form and evolve? Are there
other systems with planets like ours, including potentially habitable
planets? The PLATO 2.0 instrument consists of 34 small aperture
telescopes (32 with 25 s readout cadence and 2 with 2.5 s candence)
providing a wide field-of-view (2232 deg <SUP>2</SUP>) and a large
photometric magnitude range (4-16 mag). It focusses on bright (4-11
mag) stars in wide fields to detect and characterize planets down to
Earth-size by photometric transits, whose masses can then be determined
by ground-based radial-velocity follow-up measurements. Asteroseismology
will be performed for these bright stars to obtain highly accurate
stellar parameters, including masses and ages. The combination of
bright targets and asteroseismology results in high accuracy for
the bulk planet parameters: 2 %, 4-10 % and 10 % for planet radii,
masses and ages, respectively. The planned baseline observing strategy
includes two long pointings (2-3 years) to detect and bulk characterize
planets reaching into the habitable zone (HZ) of solar-like stars
and an additional step-and-stare phase to cover in total about 50 %
of the sky. PLATO 2.0 will observe up to 1,000,000 stars and detect
and characterize hundreds of small planets, and thousands of planets
in the Neptune to gas giant regime out to the HZ. It will therefore
provide the first large-scale catalogue of bulk characterized planets
with accurate radii, masses, mean densities and ages. This catalogue
will include terrestrial planets at intermediate orbital distances,
where surface temperatures are moderate. Coverage of this parameter
range with statistical numbers of bulk characterized planets is unique
to PLATO 2.0. The PLATO 2.0 catalogue allows us to e.g.: - complete
our knowledge of planet diversity for low-mass objects, - correlate the
planet mean density-orbital distance distribution with predictions from
planet formation theories,- constrain the influence of planet migration
and scattering on the architecture of multiple systems, and - specify
how planet and system parameters change with host star characteristics,
such as type, metallicity and age. The catalogue will allow us to study
planets and planetary systems at different evolutionary phases. It
will further provide a census for small, low-mass planets. This will
serve to identify objects which retained their primordial hydrogen
atmosphere and in general the typical characteristics of planets
in such low-mass, low-density range. Planets detected by PLATO 2.0
will orbit bright stars and many of them will be targets for future
atmosphere spectroscopy exploring their atmosphere. Furthermore,
the mission has the potential to detect exomoons, planetary rings,
binary and Trojan planets. The planetary science possible with PLATO
2.0 is complemented by its impact on stellar and galactic science via
asteroseismology as well as light curves of all kinds of variable stars,
together with observations of stellar clusters of different ages. This
will allow us to improve stellar models and study stellar activity. A
large number of well-known ages from red giant stars will probe the
structure and evolution of our Galaxy. Asteroseismic ages of bright
stars for different phases of stellar evolution allow calibrating
stellar age-rotation relationships. Together with the results of ESA's
Gaia mission, the results of PLATO 2.0 will provide a huge legacy to
planetary, stellar and galactic science.
---------------------------------------------------------
Title: Erratum: "Differential Rotation in Main-sequence
Solar-like Stars: Qualitative Inference from Asteroseismic Data"
<A href="/abs/2014Apj...790..121N">(2014, Apj, 790, 121)</A>
Authors: Nørup Lund, Mikkel; Miesch, Mark S.; Christensen-Dalsgaard,
Jørgen
2014ApJ...794...96N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Properties of 42 Solar-type Kepler Targets from the
Asteroseismic Modeling Portal
Authors: Metcalfe, T. S.; Creevey, O. L.; Doğan, G.; Mathur, S.;
Xu, H.; Bedding, T. R.; Chaplin, W. J.; Christensen-Dalsgaard, J.;
Karoff, C.; Trampedach, R.; Benomar, O.; Brown, B. P.; Buzasi, D. L.;
Campante, T. L.; Çelik, Z.; Cunha, M. S.; Davies, G. R.; Deheuvels,
S.; Derekas, A.; Di Mauro, M. P.; García, R. A.; Guzik, J. A.;
Howe, R.; MacGregor, K. B.; Mazumdar, A.; Montalbán, J.; Monteiro,
M. J. P. F. G.; Salabert, D.; Serenelli, A.; Stello, D.; Ste&şacute;
licki, M.; Suran, M. D.; Yıldız, M.; Aksoy, C.; Elsworth, Y.;
Gruberbauer, M.; Guenther, D. B.; Lebreton, Y.; Molaverdikhani, K.;
Pricopi, D.; Simoniello, R.; White, T. R.
2014ApJS..214...27M Altcode: 2014arXiv1402.3614M
Recently the number of main-sequence and subgiant stars exhibiting
solar-like oscillations that are resolved into individual mode
frequencies has increased dramatically. While only a few such data
sets were available for detailed modeling just a decade ago, the
Kepler mission has produced suitable observations for hundreds of
new targets. This rapid expansion in observational capacity has been
accompanied by a shift in analysis and modeling strategies to yield
uniform sets of derived stellar properties more quickly and easily. We
use previously published asteroseismic and spectroscopic data sets
to provide a uniform analysis of 42 solar-type Kepler targets from
the Asteroseismic Modeling Portal. We find that fitting the individual
frequencies typically doubles the precision of the asteroseismic radius,
mass, and age compared to grid-based modeling of the global oscillation
properties, and improves the precision of the radius and mass by about
a factor of three over empirical scaling relations. We demonstrate
the utility of the derived properties with several applications.
---------------------------------------------------------
Title: Differential Rotation in Main-sequence Solar-like Stars:
Qualitative Inference from Asteroseismic Data
Authors: Lund, Mikkel N.; Miesch, Mark S.; Christensen-Dalsgaard,
Jørgen
2014ApJ...790..121L Altcode: 2014arXiv1406.7873L; 2014arXiv1406.7873N
Understanding differential rotation of Sun-like stars is of great
importance for insight into the angular momentum transport in
these stars. One means of gaining such information is that of
asteroseismology. By a forward modeling approach we analyze in a
qualitative manner the impact of different differential rotation
profiles on the splittings of p-mode oscillation frequencies. The
optimum modes for inference on differential rotation are identified
along with the best value of the stellar inclination angle. We find
that in general it is not likely that asteroseismology can be used
to make an unambiguous distinction between a rotation profile such
as a conical Sun-like profile and a cylindrical profile. In addition,
it seems unlikely that asteroseismology of Sun-like stars will result
in inferences on the radial profile of the differential rotation, such
as can be done for red giants. At best, one could possibly obtain the
sign of the radial differential rotation gradient. Measurements of
the extent of the latitudinal differential from frequency splitting
are, however, more promising. One very interesting aspect that could
likely be tested from frequency splittings is whether the differential
rotation is solar-like or anti-solar-like in nature, in the sense that
a solar-like profile has an equator rotating faster than the poles.
---------------------------------------------------------
Title: Transiting Exoplanet Survey Satellite (TESS)
Authors: Ricker, George R.; Winn, Joshua N.; Vanderspek, Roland;
Latham, David W.; Bakos, Gáspár. Á.; Bean, Jacob L.; Berta-Thompson,
Zachory K.; Brown, Timothy M.; Buchhave, Lars; Butler, Nathaniel
R.; Butler, R. Paul; Chaplin, William J.; Charbonneau, David;
Christensen-Dalsgaard, Jørgen; Clampin, Mark; Deming, Drake; Doty,
John; De Lee, Nathan; Dressing, Courtney; Dunham, E. W.; Endl, Michael;
Fressin, Francois; Ge, Jian; Henning, Thomas; Holman, Matthew J.;
Howard, Andrew W.; Ida, Shigeru; Jenkins, Jon; Jernigan, Garrett;
Johnson, John A.; Kaltenegger, Lisa; Kawai, Nobuyuki; Kjeldsen, Hans;
Laughlin, Gregory; Levine, Alan M.; Lin, Douglas; Lissauer, Jack J.;
MacQueen, Phillip; Marcy, Geoffrey; McCullough, P. R.; Morton, Timothy
D.; Narita, Norio; Paegert, Martin; Palle, Enric; Pepe, Francesco;
Pepper, Joshua; Quirrenbach, Andreas; Rinehart, S. A.; Sasselov,
Dimitar; Sato, Bun'ei; Seager, Sara; Sozzetti, Alessandro; Stassun,
Keivan G.; Sullivan, Peter; Szentgyorgyi, Andrew; Torres, Guillermo;
Udry, Stephane; Villasenor, Joel
2014SPIE.9143E..20R Altcode: 2014arXiv1406.0151R
The Transiting Exoplanet Survey Satellite (TESS ) will search for
planets transiting bright and nearby stars. TESS has been selected
by NASA for launch in 2017 as an Astrophysics Explorer mission. The
spacecraft will be placed into a highly elliptical 13.7-day orbit
around the Earth. During its two-year mission, TESS will employ
four wide-field optical CCD cameras to monitor at least 200,000
main-sequence dwarf stars with I<SUB>C</SUB> (approximately less than)
13 for temporary drops in brightness caused by planetary transits. Each
star will be observed for an interval ranging from one month to one
year, depending mainly on the star's ecliptic latitude. The longest
observing intervals will be for stars near the ecliptic poles, which
are the optimal locations for follow-up observations with the James
Webb Space Telescope. Brightness measurements of preselected target
stars will be recorded every 2 min, and full frame images will be
recorded every 30 min. TESS stars will be 10-100 times brighter than
those surveyed by the pioneering Kepler mission. This will make TESS
planets easier to characterize with follow-up observations. TESS is
expected to find more than a thousand planets smaller than Neptune,
including dozens that are comparable in size to the Earth. Public data
releases will occur every four months, inviting immediate community-wide
efforts to study the new planets. The TESS legacy will be a catalog
of the nearest and brightest stars hosting transiting planets, which
will endure as highly favorable targets for detailed investigations.
---------------------------------------------------------
Title: Improvements to stellar structure models, based on a grid of
3D convection simulations - I. T(τ) relations
Authors: Trampedach, Regner; Stein, Robert F.; Christensen-Dalsgaard,
Jørgen; Nordlund, Åke; Asplund, Martin
2014MNRAS.442..805T Altcode: 2014arXiv1405.0236T
Relations between temperature, T, and optical depth, τ, are often
used for describing the photospheric transition from optically thick
to optically thin in stellar structure models. We show that this is
well justified, but also that currently used T(τ) relations are often
inconsistent with their implementation. As an outer boundary condition
on the system of stellar structure equations, T(τ) relations have an
undue effect on the overall structure of stars. In this age of precision
asteroseismology, we need to re-assess both the method for computing
and for implementing T(τ) relations, and the assumptions they rest
on. We develop a formulation for proper and consistent evaluation
of T(τ) relations from arbitrary 1D or 3D stellar atmospheres,
and for their implementation in stellar structure and evolution
models. We extract radiative T(τ) relations, as described by our
new formulation, from 3D simulations of convection in deep stellar
atmospheres of late-type stars from dwarfs to giants. These simulations
employ realistic opacities and equation of state, and account for
line blanketing. For comparison, we also extract T(τ) relations from
1DMARCSmodel atmospheres using the same formulation. T(τ) relations
from our grid of 3D convection simulations display a larger range of
behaviours with surface gravity, compared with those of conventional
theoretical 1D hydrostatic atmosphere models based on the mixing-length
theory for convection. The 1D atmospheres show little dependence on
gravity. 1D atmospheres of main-sequence stars also show an abrupt
transition to the diffusion approximation at τ ≃ 2.5, whereas the
3D simulations exhibit smooth transitions that occur at the same depth
for M ≃ 0.8 M<SUB>⊙</SUB>, and higher in the atmosphere for both
more and less massive main-sequence stars. Based on these results,
we recommend no longer using scaled solar T(τ) relations. Files with
T(τ) relations for our grid of simulations are made available to the
community, together with routines for interpolating in this irregular
grid. We also provide matching tables of atmospheric opacity, for
consistent implementation in stellar structure models.
---------------------------------------------------------
Title: Kepler-93b: A Terrestrial World Measured to within 120 km,
and a Test Case for a New Spitzer Observing Mode
Authors: Ballard, Sarah; Chaplin, William J.; Charbonneau,
David; Désert, Jean-Michel; Fressin, Francois; Zeng, Li; Werner,
Michael W.; Davies, Guy R.; Silva Aguirre, Victor; Basu, Sarbani;
Christensen-Dalsgaard, Jørgen; Metcalfe, Travis S.; Stello, Dennis;
Bedding, Timothy R.; Campante, Tiago L.; Handberg, Rasmus; Karoff,
Christoffer; Elsworth, Yvonne; Gilliland, Ronald L.; Hekker, Saskia;
Huber, Daniel; Kawaler, Steven D.; Kjeldsen, Hans; Lund, Mikkel N.;
Lundkvist, Mia
2014ApJ...790...12B Altcode: 2014arXiv1405.3659B
We present the characterization of the Kepler-93 exoplanetary
system, based on three years of photometry gathered by the Kepler
spacecraft. The duration and cadence of the Kepler observations,
in tandem with the brightness of the star, enable unusually precise
constraints on both the planet and its host. We conduct an asteroseismic
analysis of the Kepler photometry and conclude that the star has an
average density of 1.652 ± 0.006 g cm<SUP>-3</SUP>. Its mass of 0.911
± 0.033 M <SUB>⊙</SUB> renders it one of the lowest-mass subjects
of asteroseismic study. An analysis of the transit signature produced
by the planet Kepler-93b, which appears with a period of 4.72673978
± 9.7 × 10<SUP>-7</SUP> days, returns a consistent but less precise
measurement of the stellar density, 1.72<SUP>+0.02</SUP><SUB>-0.28</SUB>
g cm<SUP>-3</SUP>. The agreement of these two values lends credence to
the planetary interpretation of the transit signal. The achromatic
transit depth, as compared between Kepler and the Spitzer Space
Telescope, supports the same conclusion. We observed seven transits
of Kepler-93b with Spitzer, three of which we conducted in a new
observing mode. The pointing strategy we employed to gather this subset
of observations halved our uncertainty on the transit radius ratio
R<SUB>P</SUB> /R <SUB>sstarf</SUB>. We find, after folding together the
stellar radius measurement of 0.919 ± 0.011 R <SUB>⊙</SUB> with the
transit depth, a best-fit value for the planetary radius of 1.481 ±
0.019 R <SUB>⊕</SUB>. The uncertainty of 120 km on our measurement
of the planet's size currently renders it one of the most precisely
measured planetary radii outside of the solar system. Together with the
radius, the planetary mass of 3.8 ± 1.5 M <SUB>⊕</SUB> corresponds
to a rocky density of 6.3 ± 2.6 g cm<SUP>-3</SUP>. After applying
a prior on the plausible maximum densities of similarly sized worlds
between 1 and 1.5 R <SUB>⊕</SUB>, we find that Kepler-93b possesses
an average density within this group.
---------------------------------------------------------
Title: Angular Momentum Transport within Evolved Low-mass Stars
Authors: Cantiello, Matteo; Mankovich, Christopher; Bildsten, Lars;
Christensen-Dalsgaard, Jørgen; Paxton, Bill
2014ApJ...788...93C Altcode: 2014arXiv1405.1419C
Asteroseismology of 1.0-2.0 M <SUB>⊙</SUB> red giants by the Kepler
satellite has enabled the first definitive measurements of interior
rotation in both first ascent red giant branch (RGB) stars and those
on the helium burning clump. The inferred rotation rates are 10-30
days for the ≈0.2 M <SUB>⊙</SUB> He degenerate cores on the
RGB and 30-100 days for the He burning core in a clump star. Using
the Modules for Experiments in Stellar Evolution code, we calculate
state-of-the-art stellar evolution models of low mass rotating stars
from the zero-age main sequence to the cooling white dwarf (WD)
stage. We include transport of angular momentum due to rotationally
induced instabilities and circulations, as well as magnetic fields in
radiative zones (generated by the Tayler-Spruit dynamo). We find that
all models fail to predict core rotation as slow as observed on the
RGB and during core He burning, implying that an unmodeled angular
momentum transport process must be operating on the early RGB of low
mass stars. Later evolution of the star from the He burning clump to
the cooling WD phase appears to be at nearly constant core angular
momentum. We also incorporate the adiabatic pulsation code, ADIPLS,
to explicitly highlight this shortfall when applied to a specific
Kepler asteroseismic target, KIC8366239.
---------------------------------------------------------
Title: Non-radial Oscillations in M-giant Semi-regular Variables:
Stellar Models and Kepler Observations
Authors: Stello, Dennis; Compton, Douglas L.; Bedding, Timothy R.;
Christensen-Dalsgaard, Jørgen; Kiss, Laszlo L.; Kjeldsen, Hans;
Bellamy, Beau; García, Rafael A.; Mathur, Savita
2014ApJ...788L..10S Altcode: 2014arXiv1406.0003S
The success of asteroseismology relies heavily on our ability to
identify the frequency patterns of stellar oscillation modes. For stars
like the Sun this is relatively easy because the mode frequencies follow
a regular pattern described by a well-founded asymptotic relation. When
a solar-like star evolves off the main sequence and onto the red giant
branch its structure changes dramatically, resulting in changes in
the frequency pattern of the modes. We follow the evolution of the
adiabatic frequency pattern from the main sequence to near the tip
of the red giant branch for a series of models. We find a significant
departure from the asymptotic relation for the non-radial modes near
the red giant branch tip, resulting in a triplet frequency pattern. To
support our investigation we analyze almost four years of Kepler data
of the most luminous stars in the field (late K and early M type)
and find that their frequency spectra indeed show a triplet pattern
dominated by dipole modes even for the most luminous stars in our
sample. Our identification explains previous results from ground-based
observations reporting fine structure in the Petersen diagram and
sub-ridges in the period-luminosity diagram. Finally, we find "new
ridges" of non-radial modes with frequencies below the fundamental mode
in our model calculations, and we speculate they are related to f modes.
---------------------------------------------------------
Title: VizieR Online Data Catalog: T(tau) relations code (Trampedach+,
2014)
Authors: Trampedach, R.; Stein, R. F.; Christensen-Dalsgaard, J.;
Nordlund, A.; Asplund, M.
2014yCat..74420805T Altcode:
Radiative T({tau})-relations, in the form of generalised Hopf functions,
computed from a grid of 37, solar metallicity, realistic, 3D convection
simulations with radiative transfer. <P />(6 data files).
---------------------------------------------------------
Title: VizieR Online Data Catalog: Small Kepler planets radial
velocities (Marcy+, 2014)
Authors: Marcy, G. W.; Isaacson, H.; Howard, A. W.; Rowe, J. F.;
Jenkins, J. M.; Bryson, S. T.; Latham, D. W.; Howell, S. B.;
Gautier, T. N., III; Batalha, N. M.; Rogers, L.; Ciardi, D.; Fischer,
D. A.; Gilliland, R. L.; Kjeldsen, H.; Christensen-Dalsgaard, J.;
Huber, D.; Chaplin, W. J.; Basu, S.; Buchhave, L. A.; Quinn, S. N.;
Borucki, W. J.; Koch, D. G.; Hunter, R.; Caldwell, D. A.; van Cleve,
J.; Kolbl, R.; Weiss, L. M.; Petigura, E.; Seager, S.; Morton, T.;
Johnson, J. A.; Ballard, S.; Burke, C.; Cochran, W. D.; Endl, M.;
MacQueen, P.; Everett, M. E.; Lissauer, J. J.; Ford, E. B.; Torres,
G.; Fressin, F.; Brown, T. M.; Steffen, J. H.; Charbonneau, D.; Basri,
G. S.; Sasselov, D. D.; Winn, J.; Sanchis-Ojeda, R.; Christiansen,
J.; Adams, E.; Henze, C.; Dupree, A.; Fabrycky, D. C.; Fortney, J. J.;
Tarter, J.; Holman, M. J.; Tenenbaum, P.; Shporer, A.; Lucas, P. W.;
Welsh, W. F.; Orosz, J. A.; Bedding, T. R.; Campante, T. L.; Davies,
G. R.; Elsworth, Y.; Handberg, R.; Hekker, S.; Karoff, C.; Kawaler,
S. D.; Lund, M. N.; Lundkvist, M.; Metcalfe, T. S.; Miglio, A.; Silva
Aguirre, V.; Stello, D.; White, T. R.; Boss, A.; Devore, E.; Gould,
A.; Prsa, A.; Agol, E.; Barclay, T.; Coughlin, J.; Brugamyer, E.;
Mullally, F.; Quintana, E. V.; Still, M.; Thompson, S. E.; Morrison,
D.; Twicken, J. D.; Desert, J. -M.; Carter, J.; Crepp, J. R.; Hebrard,
G.; Santerne, A.; Moutou, C.; Sobeck, C.; Hudgins, D.; Haas, M. R.;
Robertson, P.; Lillo-Box, J.; Barrado, D.
2014yCat..22100020M Altcode:
Here we report measured masses, radii, and densities (or upper limits
on those values) for 42 transiting planet candidates contained within
22 bright Kepler Objects of Interest (KOIs) from Batalha et al. (2013,
Cat. J/ApJS/204/24). We carried out multiple Doppler-shift measurements
of the host stars using the Keck 1 telescope. From the spectroscopy
and Doppler measurements, we compute self-consistent measurements of
stellar and planet radii, employing either stellar structure models
or asteroseismology measurements from the Kepler photometry. We also
search for (and report) 7 additional non-transiting planets revealed
by the precise radial velocities (RVs), for a total of 49 planets. <P
/>We carried out "reconnaissance" high-resolution spectroscopy on ~1000
KOIs with spectral resolution, R~50000, and S/N=20-100 per pixel. The
dual goals were searching for false positives and refining the stellar
parameters. We obtained one or two such reconnaissance spectra using
one of four facilities: the McDonald Observatory 2.7m, the Tillinghast
1.5m on Mt. Hopkins, the Lick Observatory 3m, and the 2.6m Nordic
Optical Telescope. <P />Speckle imaging of each of the selected 22
KOIs was obtained using the two-color DSSI speckle camera at the WIYN
3.5m telescope on Kitt Peak. <P />All 22 KOIs were observed with the
Keck NIRC2-AO system. <P />(3 data files).
---------------------------------------------------------
Title: Seismic constraints on the radial dependence of the internal
rotation profiles of six Kepler subgiants and young red giants
Authors: Deheuvels, S.; Doğan, G.; Goupil, M. J.; Appourchaux, T.;
Benomar, O.; Bruntt, H.; Campante, T. L.; Casagrande, L.; Ceillier,
T.; Davies, G. R.; De Cat, P.; Fu, J. N.; García, R. A.; Lobel,
A.; Mosser, B.; Reese, D. R.; Regulo, C.; Schou, J.; Stahn, T.;
Thygesen, A. O.; Yang, X. H.; Chaplin, W. J.; Christensen-Dalsgaard,
J.; Eggenberger, P.; Gizon, L.; Mathis, S.; Molenda-Żakowicz, J.;
Pinsonneault, M.
2014A&A...564A..27D Altcode: 2014arXiv1401.3096D
Context. We still do not understand which physical mechanisms are
responsible for the transport of angular momentum inside stars. The
recent detection of mixed modes that contain the clear signature of
rotation in the spectra of Kepler subgiants and red giants gives us
the opportunity to make progress on this question. <BR /> Aims: Our
aim is to probe the radial dependence of the rotation profiles for a
sample of Kepler targets. For this purpose, subgiants and early red
giants are particularly interesting targets because their rotational
splittings are more sensitive to the rotation outside the deeper core
than is the case for their more evolved counterparts. <BR /> Methods:
We first extracted the rotational splittings and frequencies of the
modes for six young Kepler red giants. We then performed a seismic
modeling of these stars using the evolutionary codes Cesam2k and
astec. By using the observed splittings and the rotational kernels
of the optimal models, we inverted the internal rotation profiles
of the six stars. <BR /> Results: We obtain estimates of the core
rotation rates for these stars, and upper limits to the rotation in
their convective envelope. We show that the rotation contrast between
the core and the envelope increases during the subgiant branch. Our
results also suggest that the core of subgiants spins up with time,
while their envelope spins down. For two of the stars, we show that a
discontinuous rotation profile with a deep discontinuity reproduces
the observed splittings significantly better than a smooth rotation
profile. Interestingly, the depths that are found to be most probable
for the discontinuities roughly coincide with the location of the
H-burning shell, which separates the layers that contract from those
that expand. <BR /> Conclusions: We characterized the differential
rotation pattern of six young giants with a range of metallicities, and
with both radiative and convective cores on the main sequence. This will
bring observational constraints to the scenarios of angular momentum
transport in stars. Moreover, if the existence of sharp gradients in
the rotation profiles of young red giants is confirmed, it is expected
to help in distinguishing between the physical processes that could
transport angular momentum in the subgiant and red giant branches. <P
/>Appendices and Tables 3-9 are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201322779/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: The PLATO 2.0 Mission
Authors: Pagano, I.; Rauer, H.; Aerts, C.; Appourchaux, T.; Benz,
W.; Brandeker, A.; Christensen-Dalsgaard, J.; Deleuil, M.; Gizon, L.;
Goupil, M. -J.; Guedel, M.; Heras, A.; Janot-Pacheco, E.; Mas-Hesse,
M.; Piotto, G.; Pollaco, D.; Ragazzoni, R.; Santos, N. C.; Smith,
A.; Suarez, J. C.; Szabo, R.; Udry, S.
2014EPSC....9..789P Altcode:
PLATO 2.0 is the M class mission selected by ESA for its M3 launch
slot in the framework of the Cosmic Vision 2015-2025 program. The main
goals of PLATO 2.0 are the detection of terrestrial exoplanets in the
habitable zone of solar-type stars and the characterization of their
bulk properties needed to determine their habitability. Moreover,
PLATO 2.0 will be key in understanding the formation, architecture,
and evolution of planetary systems thanks to a thorough inventory
of the physical properties of thousands of rocky, icy, and gaseous
giant planets. We will illustrate the PLATO 2.0 science goals, how
the instrument is conceived to fulfil the science requirements, and
how the project is organized to implement the instrument, plan the
observations, and exploit the resulting data.
---------------------------------------------------------
Title: Old Puzzle, New Insights: A Lithium-rich Giant Quietly Burning
Helium in Its Core
Authors: Silva Aguirre, V.; Ruchti, G. R.; Hekker, S.; Cassisi, S.;
Christensen-Dalsgaard, J.; Datta, A.; Jendreieck, A.; Jessen-Hansen,
J.; Mazumdar, A.; Mosser, B.; Stello, D.; Beck, P. G.; de Ridder, J.
2014ApJ...784L..16S Altcode: 2014arXiv1402.6339S
About 1% of giant stars have been shown to have large surface Li
abundances, which is unexpected according to standard stellar evolution
models. Several scenarios for lithium production have been proposed,
but it is still unclear why these Li-rich giants exist. A missing piece
in this puzzle is the knowledge of the exact stage of evolution of these
stars. Using low- and-high-resolution spectroscopic observations, we
have undertaken a survey of lithium-rich giants in the Kepler field. In
this Letter, we report the finding of the first confirmed Li-rich
core-helium-burning giant, as revealed by asteroseismic analysis. The
evolutionary timescales constrained by its mass suggest that Li
production most likely took place through non-canonical mixing at the
RGB tip, possibly during the helium flash. <P />Based on observations
made with the Nordic Optical Telescope, operated by the Nordic Optical
Telescope Scientific Association at the Observatorio del Roque de
los Muchachos, La Palma, Spain, of the Instituto de Astrofísica
de Canarias.
---------------------------------------------------------
Title: Limits on Surface Gravities of Kepler Planet-candidate Host
Stars from Non-detection of Solar-like Oscillations
Authors: Campante, T. L.; Chaplin, W. J.; Lund, M. N.; Huber, D.;
Hekker, S.; García, R. A.; Corsaro, E.; Handberg, R.; Miglio, A.;
Arentoft, T.; Basu, S.; Bedding, T. R.; Christensen-Dalsgaard, J.;
Davies, G. R.; Elsworth, Y. P.; Gilliland, R. L.; Karoff, C.; Kawaler,
S. D.; Kjeldsen, H.; Lundkvist, M.; Metcalfe, T. S.; Silva Aguirre,
V.; Stello, D.
2014ApJ...783..123C Altcode: 2014arXiv1401.6324C
We present a novel method for estimating lower-limit surface gravities
(log g) of Kepler targets whose data do not allow the detection of
solar-like oscillations. The method is tested using an ensemble of
solar-type stars observed in the context of the Kepler Asteroseismic
Science Consortium. We then proceed to estimate lower-limit log g for a
cohort of Kepler solar-type planet-candidate host stars with no detected
oscillations. Limits on fundamental stellar properties, as provided
by this work, are likely to be useful in the characterization of the
corresponding candidate planetary systems. Furthermore, an important
byproduct of the current work is the confirmation that amplitudes of
solar-like oscillations are suppressed in stars with increased levels
of surface magnetic activity.
---------------------------------------------------------
Title: Study of KIC 8561221 observed by Kepler: an early red giant
showing depressed dipolar modes
Authors: García, R. A.; Pérez Hernández, F.; Benomar, O.; Silva
Aguirre, V.; Ballot, J.; Davies, G. R.; Doğan, G.; Stello, D.;
Christensen-Dalsgaard, J.; Houdek, G.; Lignières, F.; Mathur, S.;
Takata, M.; Ceillier, T.; Chaplin, W. J.; Mathis, S.; Mosser, B.;
Ouazzani, R. M.; Pinsonneault, M. H.; Reese, D. R.; Régulo, C.;
Salabert, D.; Thompson, M. J.; van Saders, J. L.; Neiner, C.; De
Ridder, J.
2014A&A...563A..84G Altcode: 2013arXiv1311.6990G
Context. The continuous high-precision photometric observations
provided by the CoRoT and Kepler space missions have allowed us to
understand the structure and dynamics of red giants better using
asteroseismic techniques. A small fraction of these stars show
dipole modes with unexpectedly low amplitudes. The reduction in
amplitude is more pronounced for stars with a higher frequency of
maximum power, ν<SUB>max</SUB>. <BR /> Aims: In this work we want to
characterise KIC 8561221 in order to confirm that it is currently the
least evolved star among this peculiar subset and to discuss several
hypotheses that could help explain the reduction of the dipole mode
amplitudes. <BR /> Methods: We used Kepler short- and long-cadence
data combined with spectroscopic observations to infer the stellar
structure and dynamics of KIC 8561221. We then discussed different
scenarios that could contribute to reducing the dipole amplitudes,
such as a fast-rotating interior or the effect of a magnetic field
on the properties of the modes. We also performed a detailed study
of the inertia and damping of the modes. <BR /> Results: We have
been able to characterise 36 oscillations modes, in particular, a
few dipole modes above ν<SUB>max</SUB> that exhibit nearly normal
amplitudes. The frequencies of all the measured modes were used
to determine the overall properties and the internal structure of
the star. We have inferred a surface rotation period of ~91 days
and uncovered a variation in the surface magnetic activity during
the last 4 years. The analysis of the convective background did not
reveal any difference compared to "normal" red giants. As expected,
the internal regions of the star probed by the ℓ = 2 and 3 modes
spin 4 to 8 times faster than the surface. <BR /> Conclusions: With
our grid of standard models we are able to properly fit the observed
frequencies. Our model calculation of mode inertia and damping give
no explanation for the depressed dipole modes. A fast-rotating core
is also ruled out as a possible explanation. Finally, we do not have
any observational evidence of a strong deep magnetic field inside the
star. <P />Table 3 and Appendix A are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201322823/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: On the inference of stellar ages and convective-core properties
in main-sequence solar-like pulsators
Authors: Brandão, I. M.; Cunha, M. S.; Christensen-Dalsgaard, J.
2014MNRAS.438.1751B Altcode: 2013arXiv1311.7600B; 2013MNRAS.tmp.2970B
Particular diagnostic tools may isolate the signature left on
the oscillation frequencies by the presence of a small convective
core. Their frequency derivative is expected to provide information
about convective core's properties and stellar age. The main goal of
this work is to study the potential of the diagnostic tools with regard
to the inference of stellar age and stellar core's properties. For
that, we computed diagnostic tools and their frequency derivatives
from the oscillation frequencies of main-sequence models with masses
between 1.0 and 1.6 M<SUB>⊙</SUB> and with different physics. We
considered the dependence of the diagnostic tools on stellar age and
on the size of the relative discontinuity in the squared sound speed
at the edge of the convectively unstable region. We find that the
absolute value of the frequency derivatives of the diagnostic tools
increases as the star evolves on the main sequence. The fraction
of stellar main-sequence evolution for models with masses >1.2
M<SUB>⊙</SUB> may be estimated from the frequency derivatives of
two of the diagnostic tools. For lower mass models, constraints on
the convective core's overshoot can potentially be derived based on
the analysis of the same derivatives. For at least 35 per cent of our
sample of stellar models, the frequency derivative of the diagnostic
tools takes its maximum absolute value on the frequency range where
observed oscillations may be expected.
---------------------------------------------------------
Title: Accurate Parameters of the Oldest Known Rocky-exoplanet
Hosting System: Kepler-10 Revisited
Authors: Fogtmann-Schulz, Alexandra; Hinrup, Brian; Van Eylen, Vincent;
Christensen-Dalsgaard, Jørgen; Kjeldsen, Hans; Silva Aguirre, Víctor;
Tingley, Brandon
2014ApJ...781...67F Altcode: 2013arXiv1311.6336F
Since the discovery of Kepler-10, the system has received considerable
interest because it contains a small, rocky planet which orbits the
star in less than a day. The system's parameters, announced by the
Kepler team and subsequently used in further research, were based on
only five months of data. We have reanalyzed this system using the full
span of 29 months of Kepler photometric data, and obtained improved
information about its star and the planets. A detailed asteroseismic
analysis of the extended time series provides a significant improvement
on the stellar parameters: not only can we state that Kepler-10 is
the oldest known rocky-planet-harboring system at 10.41 ± 1.36 Gyr,
but these parameters combined with improved planetary parameters from
new transit fits gives us the radius of Kepler-10b to within just
125 km. A new analysis of the full planetary phase curve leads to
new estimates on the planetary temperature and albedo, which remain
degenerate in the Kepler band. Our modeling suggests that the flux
level during the occultation is slightly lower than at the transit
wings, which would imply that the nightside of this planet has a
non-negligible temperature.
---------------------------------------------------------
Title: Concluding remarks
Authors: Christensen-Dalsgaard, Jørgen; Kawaler, Steven D.
2014IAUS..301..359C Altcode:
We cannot presume to summarize all of the science we've discussed in
the talks, posters, and informal discussions. Here, we discuss a few of
the themes that emerged, concentrating on the theoretical basis that
Wojtek Dziembowiski and his colleagues have developed and explored
over the past 40+ years. We connect those with observational results
- especially those from recent ground-based surveys and space-based
missions that have revolutionized the study of stellar variability.
---------------------------------------------------------
Title: Stellar Observations Network Group: The prototype is nearly
ready
Authors: Grundahl, Frank; Christensen-Dalsgaard, Jørgen; Pallé,
Pere L.; Andersen, Mads F.; Frandsen, Søren; Harpsøe, Kennet;
Jørgensen, Uffe Gråe; Kjeldsen, Hans; Rasmussen, Per K.; Skottfelt,
Jesper; Sørensen, Anton N.; Hage, Andrea Triviño
2014IAUS..301...69G Altcode:
The prototype telescope and instruments for the Stellar Observations
Network Group (SONG) are nearing completion at the Observatorio del
Teide on Tenerife. In this contribution we describe the current status
(autumn 2013) of the telescope and its instrumentation. Preliminary
performance characteristics are presented for the high-resolution
spectrograph based on daytime observations of the Sun and a 4 hour
test series obtained for the sub-giant β Aquilae.
---------------------------------------------------------
Title: Detection of l = 4 and l = 5 Modes in 12 Years of Solar
VIRGO-SPM Data—Tests on Kepler Observations of 16 Cyg A and B
Authors: Lund, Mikkel Nørup; Kjeldsen, Hans; Christensen-Dalsgaard,
Jørgen; Handberg, Rasmus; Silva Aguirre, Victor
2014ApJ...782....2L Altcode: 2014arXiv1401.7003N
We present the detection of l = 4 and l = 5 modes in power spectra of
the Sun, constructed from 12 yr full-disk VIRGO-SPM data sets. A method
for enhancing the detectability of these modes in asteroseismic targets
is presented and applied to Kepler data of the two solar analogues 16
Cyg A and B. For these targets, we see indications of a signal from l =
4 modes, while nothing is yet seen for l = 5 modes. We further simulate
the power spectra of these stars and from this we estimate that it
should indeed be possible to see such indications of l = 4 modes at
the present length of the data sets. In the simulation process, we
briefly look into the apparent misfit between observed and calculated
mode visibilities. We predict that firm detections of at least l =
4 should be possible in any case at the end of the Kepler mission. For
l = 5, we do not predict any firm detections from Kepler data.
---------------------------------------------------------
Title: Measurement of Acoustic Glitches in Solar-type Stars from
Oscillation Frequencies Observed by Kepler
Authors: Mazumdar, A.; Monteiro, M. J. P. F. G.; Ballot, J.; Antia,
H. M.; Basu, S.; Houdek, G.; Mathur, S.; Cunha, M. S.; Silva Aguirre,
V.; García, R. A.; Salabert, D.; Verner, G. A.; Christensen-Dalsgaard,
J.; Metcalfe, T. S.; Sanderfer, D. T.; Seader, S. E.; Smith, J. C.;
Chaplin, W. J.
2014ApJ...782...18M Altcode: 2013arXiv1312.4907M
For the very best and brightest asteroseismic solar-type targets
observed by Kepler, the frequency precision is sufficient to determine
the acoustic depths of the surface convective layer and the helium
ionization zone. Such sharp features inside the acoustic cavity of
the star, which we call acoustic glitches, create small oscillatory
deviations from the uniform spacing of frequencies in a sequence of
oscillation modes with the same spherical harmonic degree. We use these
oscillatory signals to determine the acoustic locations of such features
in 19 solar-type stars observed by the Kepler mission. Four independent
groups of researchers utilized the oscillation frequencies themselves,
the second differences of the frequencies and the ratio of the small
and large separation to locate the base of the convection zone and the
second helium ionization zone. Despite the significantly different
methods of analysis, good agreement was found between the results
of these four groups, barring a few cases. These results also agree
reasonably well with the locations of these layers in representative
models of the stars. These results firmly establish the presence of
the oscillatory signals in the asteroseismic data and the viability
of several techniques to determine the location of acoustic glitches
inside stars.
---------------------------------------------------------
Title: Asteroseismology of red giants
Authors: Christensen-Dalsgaard, Jørgen
2014aste.book..194C Altcode: 2011arXiv1106.5946C
Red-giant stars are emerging as one of the most interesting areas of
space asteroseismology. Even a relatively basic analysis leads to the
determination of the global parameters of the stars, such as their mass
and radius, and the very extensive space-based data now available for a
large number of stars allow detailed investigation of the deep interiors
of red giants, including distinguishing between stars that do and do
not have helium fusion in the core, on the basis of periods of gravity
waves partially trapped in the core. Here I review the theoretical
background for these new developments and provide a simple explanation
for the effect on the period spacing of central helium fusion.
---------------------------------------------------------
Title: The evolution of the internal rotation of solar-type stars
Authors: Di Mauro, Maria Pia; Ventura, Rita; Cardini, Daniela;
Christensen-Dalsgaard, Jørgen; Dziembowski, Wojciech A.; Paternò,
Lucio
2014IAUS..301..345D Altcode:
We discuss the potential of asteroseismic inversion to study the
internal dynamics of solar-type stars and to reconstruct the evolution
of the internal rotation from the main sequence to the red-giant
phase. In particular, we consider the use of gravity and mixed modes
and the application of different inversion methods.
---------------------------------------------------------
Title: What Asteroseismology can do for Exoplanets: Kepler-410A
b is a Small Neptune around a Bright Star, in an Eccentric Orbit
Consistent with Low Obliquity
Authors: Van Eylen, V.; Lund, M. N.; Silva Aguirre, V.; Arentoft, T.;
Kjeldsen, H.; Albrecht, S.; Chaplin, W. J.; Isaacson, H.; Pedersen,
M. G.; Jessen-Hansen, J.; Tingley, B.; Christensen-Dalsgaard, J.;
Aerts, C.; Campante, T. L.; Bryson, S. T.
2014ApJ...782...14V Altcode: 2013arXiv1312.4938V
We confirm the Kepler planet candidate Kepler-410A b (KOI-42b) as a
Neptune-sized exoplanet on a 17.8 day, eccentric orbit around the
bright (K <SUB>p</SUB> = 9.4) star Kepler-410A (KOI-42A). This is
the third brightest confirmed planet host star in the Kepler field
and one of the brightest hosts of all currently known transiting
exoplanets. Kepler-410 consists of a blend between the fast rotating
planet host star (Kepler-410A) and a fainter star (Kepler-410B), which
has complicated the confirmation of the planetary candidate. Employing
asteroseismology, using constraints from the transit light curve,
adaptive optics and speckle images, and Spitzer transit observations,
we demonstrate that the candidate can only be an exoplanet orbiting
Kepler-410A. We determine via asteroseismology the following stellar
and planetary parameters with high precision; M <SUB>sstarf</SUB> =
1.214 ± 0.033 M <SUB>⊙</SUB>, R <SUB>sstarf</SUB> = 1.352 ± 0.010 R
<SUB>⊙</SUB>, age =2.76 ± 0.54 Gyr, planetary radius (2.838 ± 0.054
R <SUB>⊕</SUB>), and orbital eccentricity (0.17^{+0.07}_{-0.06}). In
addition, rotational splitting of the pulsation modes allows for
a measurement of Kepler-410A's inclination and rotation rate. Our
measurement of an inclination of 82.5^{+7.5}_{-2.5} [°] indicates
a low obliquity in this system. Transit timing variations indicate
the presence of at least one additional (non-transiting) planet
(Kepler-410A c) in the system.
---------------------------------------------------------
Title: Masses, Radii, and Orbits of Small Kepler Planets: The
Transition from Gaseous to Rocky Planets
Authors: Marcy, Geoffrey W.; Isaacson, Howard; Howard, Andrew W.;
Rowe, Jason F.; Jenkins, Jon M.; Bryson, Stephen T.; Latham, David
W.; Howell, Steve B.; Gautier, Thomas N., III; Batalha, Natalie M.;
Rogers, Leslie; Ciardi, David; Fischer, Debra A.; Gilliland, Ronald
L.; Kjeldsen, Hans; Christensen-Dalsgaard, Jørgen; Huber, Daniel;
Chaplin, William J.; Basu, Sarbani; Buchhave, Lars A.; Quinn, Samuel
N.; Borucki, William J.; Koch, David G.; Hunter, Roger; Caldwell,
Douglas A.; Van Cleve, Jeffrey; Kolbl, Rea; Weiss, Lauren M.;
Petigura, Erik; Seager, Sara; Morton, Timothy; Johnson, John Asher;
Ballard, Sarah; Burke, Chris; Cochran, William D.; Endl, Michael;
MacQueen, Phillip; Everett, Mark E.; Lissauer, Jack J.; Ford, Eric
B.; Torres, Guillermo; Fressin, Francois; Brown, Timothy M.; Steffen,
Jason H.; Charbonneau, David; Basri, Gibor S.; Sasselov, Dimitar D.;
Winn, Joshua; Sanchis-Ojeda, Roberto; Christiansen, Jessie; Adams,
Elisabeth; Henze, Christopher; Dupree, Andrea; Fabrycky, Daniel C.;
Fortney, Jonathan J.; Tarter, Jill; Holman, Matthew J.; Tenenbaum,
Peter; Shporer, Avi; Lucas, Philip W.; Welsh, William F.; Orosz,
Jerome A.; Bedding, T. R.; Campante, T. L.; Davies, G. R.; Elsworth,
Y.; Handberg, R.; Hekker, S.; Karoff, C.; Kawaler, S. D.; Lund,
M. N.; Lundkvist, M.; Metcalfe, T. S.; Miglio, A.; Silva Aguirre, V.;
Stello, D.; White, T. R.; Boss, Alan; Devore, Edna; Gould, Alan; Prsa,
Andrej; Agol, Eric; Barclay, Thomas; Coughlin, Jeff; Brugamyer, Erik;
Mullally, Fergal; Quintana, Elisa V.; Still, Martin; Thompson, Susan
E.; Morrison, David; Twicken, Joseph D.; Désert, Jean-Michel; Carter,
Josh; Crepp, Justin R.; Hébrard, Guillaume; Santerne, Alexandre;
Moutou, Claire; Sobeck, Charlie; Hudgins, Douglas; Haas, Michael R.;
Robertson, Paul; Lillo-Box, Jorge; Barrado, David
2014ApJS..210...20M Altcode: 2014arXiv1401.4195M
We report on the masses, sizes, and orbits of the planets orbiting
22 Kepler stars. There are 49 planet candidates around these stars,
including 42 detected through transits and 7 revealed by precise
Doppler measurements of the host stars. Based on an analysis of the
Kepler brightness measurements, along with high-resolution imaging and
spectroscopy, Doppler spectroscopy, and (for 11 stars) asteroseismology,
we establish low false-positive probabilities (FPPs) for all of the
transiting planets (41 of 42 have an FPP under 1%), and we constrain
their sizes and masses. Most of the transiting planets are smaller
than three times the size of Earth. For 16 planets, the Doppler
signal was securely detected, providing a direct measurement of the
planet's mass. For the other 26 planets we provide either marginal mass
measurements or upper limits to their masses and densities; in many
cases we can rule out a rocky composition. We identify six planets
with densities above 5 g cm<SUP>-3</SUP>, suggesting a mostly rocky
interior for them. Indeed, the only planets that are compatible with a
purely rocky composition are smaller than ~2 R <SUB>⊕</SUB>. Larger
planets evidently contain a larger fraction of low-density material (H,
He, and H<SUB>2</SUB>O). <P />Based in part on observations obtained
at the W. M. Keck Observatory, which is operated by the University of
California and the California Institute of Technology.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Asteroseismic study of solar-type
stars (Chaplin+, 2014)
Authors: Chaplin, W. J.; Basu, S.; Huber, D.; Serenelli, A.;
Casagrande, L.; Silva Aguirre, V.; Ball, W. H.; Creevey, O. L.;
Gizon, L.; Handberg, R.; Karoff, C.; Lutz, R.; Marques, J. P.;
Miglio, A.; Stello, D.; Suran, M. D.; Pricopi, D.; Metcalfe, T. S.;
Monteiro, M. J. P. F. G.; Molenda-Zakowicz, J.; Appourchaux, T.;
Christensen-Dalsgaard, J.; Elsworth, Y.; Garcia, R. A.; Houdek, G.;
Kjeldsen, H.; Bonanno, A.; Campante, T. L.; Corsaro, E.; Gaulme, P.;
Hekker, S.; Mathur, S.; Mosser, B.; Regulo, C.; Salabert, D.
2014yCat..22100001C Altcode:
During the first 10 months of science operations more than 2000
solar-type stars were selected by the Kepler Asteroseismic Science
Consortium (KASC) to be observed as part of an asteroseismic survey
of the Sun-like population in the Kepler field of view. Solar-like
oscillations were detected by Kepler in more than 500 stars (Chaplin
et al. 2011Sci...332..213C), and from these data robust global or
average asteroseismic parameters were determined for all targets in the
sample. These asteroseismic parameters allow us to estimate fundamental
properties of the stars. In this paper we present stellar properties
- namely masses, radii, surface gravities, mean densities and ages -
of this asteroseismic sample of main-sequence and subgiant stars. <P
/>(5 data files).
---------------------------------------------------------
Title: Asteroseismic Fundamental Properties of Solar-type Stars
Observed by the NASA Kepler Mission
Authors: Chaplin, W. J.; Basu, S.; Huber, D.; Serenelli, A.;
Casagrande, L.; Silva Aguirre, V.; Ball, W. H.; Creevey, O. L.;
Gizon, L.; Handberg, R.; Karoff, C.; Lutz, R.; Marques, J. P.;
Miglio, A.; Stello, D.; Suran, M. D.; Pricopi, D.; Metcalfe, T. S.;
Monteiro, M. J. P. F. G.; Molenda-Żakowicz, J.; Appourchaux, T.;
Christensen-Dalsgaard, J.; Elsworth, Y.; García, R. A.; Houdek, G.;
Kjeldsen, H.; Bonanno, A.; Campante, T. L.; Corsaro, E.; Gaulme, P.;
Hekker, S.; Mathur, S.; Mosser, B.; Régulo, C.; Salabert, D.
2014ApJS..210....1C Altcode: 2013arXiv1310.4001C
We use asteroseismic data obtained by the NASA Kepler mission to
estimate the fundamental properties of more than 500 main-sequence and
sub-giant stars. Data obtained during the first 10 months of Kepler
science operations were used for this work, when these solar-type
targets were observed for one month each in survey mode. Stellar
properties have been estimated using two global asteroseismic parameters
and complementary photometric and spectroscopic data. Homogeneous sets
of effective temperatures, T <SUB>eff</SUB>, were available for the
entire ensemble from complementary photometry; spectroscopic estimates
of T <SUB>eff</SUB> and [Fe/H] were available from a homogeneous
analysis of ground-based data on a subset of 87 stars. We adopt
a grid-based analysis, coupling six pipeline codes to 11 stellar
evolutionary grids. Through use of these different grid-pipeline
combinations we allow implicitly for the impact on the results of
stellar model dependencies from commonly used grids, and differences
in adopted pipeline methodologies. By using just two global parameters
as the seismic inputs we are able to perform a homogenous analysis
of all solar-type stars in the asteroseismic cohort, including many
targets for which it would not be possible to provide robust estimates
of individual oscillation frequencies (due to a combination of low
signal-to-noise ratio and short dataset lengths). The median final
quoted uncertainties from consolidation of the grid-based analyses
are for the full ensemble (spectroscopic subset) approximately 10.8%
(5.4%) in mass, 4.4% (2.2%) in radius, 0.017 dex (0.010 dex) in log g,
and 4.3% (2.8%) in mean density. Around 36% (57%) of the stars have
final age uncertainties smaller than 1 Gyr. These ages will be useful
for ensemble studies, but should be treated carefully on a star-by-star
basis. Future analyses using individual oscillation frequencies will
offer significant improvements on up to 150 stars, in particular for
estimates of the ages, where having the individual frequency data is
most important.
---------------------------------------------------------
Title: Benefits of multiple sites for asteroseismic detections
Authors: Arentoft, T.; Tingley, B.; Christensen-Dalsgaard, J.;
Kjeldsen, H.; White, T. R.; Grundahl, F.
2014MNRAS.437.1318A Altcode: 2013arXiv1310.2845A; 2013MNRAS.tmp.2654A
While Kepler has pushed the science of asteroseismology to limits
unimaginable a decade ago, the need for asteroseismic studies of
individual objects remains. This is primarily due to the limitations of
single-colour intensity variations, which are much less sensitive to
certain asteroseismic signals. The best way to obtain the necessary
data is via very high resolution ground-based spectrography. Such
observations measure the perceived radial-velocity shifts that arise due
to stellar oscillations, which exhibit a much better signal-to-noise
ratio than those for intensity observations. Stellar Observations
Network Group (SONG), a proposed network of 1 m telescopes with
spectrographs that can reach R = 110 000, was designed with this need
in mind. With one node under commissioning in Tenerife and another
under construction in China, an analysis of the scientific benefits
of constructing additional nodes for the network is warranted. By
convolving models of asteroseismic observables (mean densities, small
separations) with the anticipated window functions for different
node configurations, we explore the impact of the number of nodes in
the SONG network on the anticipated results, across the areas of the
Hertzsprung-Russell diagram where solar-like oscillations are found. We
find that although time series from two SONG nodes, or in some cases
even one node, will allow us to detect oscillations; the full SONG
network, providing full temporal coverage, is needed for obtaining
the science goals of SONG, including analysis of modes of spherical
harmonic degree l = 3.
---------------------------------------------------------
Title: Inferring properties of small convective cores in main-sequence
solar-like pulsators
Authors: Brandão, I. M.; Cunha, M. S.; Christensen-Dalsgaard, J.
2013EAS....63..115B Altcode: 2014arXiv1401.1832B
This work concerns the study of the properties of convective cores in
main-sequence models of solar-like pulsators and what information they
may hold about stellar ages. We verified that the maximum absolute
frequency derivative of particular combinations of frequencies,
which we name "the slopes", provides information on the relative
size of the discontinuity in the sound-speed profile at the border
of the convectively mixed region. Since the latter is related to the
evolutionary state of stars, we show that for models with masses above
1.3M<SUB>⊙</SUB>, it may be possible to estimate the fraction of
stellar main-sequence evolution from the slopes. Moreover, for models
with masses below 1.2M<SUB>⊙</SUB> we verified that it may be possible
to use the slopes to discriminate against models with small amounts
of core overshoot.
---------------------------------------------------------
Title: The Torsional Oscillation and the Timing of the Solar Cycle:
Is it Maximum Yet?
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R.;
Larson, T. P.; Schou, J.; Thompson, M. J.
2013ASPC..478..303H Altcode:
After the late start to Cycle 24 there are some indications that
activity may have peaked as early as late 2011 and that the polar-field
reversal has already occurred in the North. We use helioseismic
measurements of the migrating zonal flow pattern known as the torsional
oscillation to estimate the length of the solar cycle, and find that
it has held steady at about 12.3 years since late 2009, which would
point to solar maximum in 2013 as expected.
---------------------------------------------------------
Title: The new era of asteroseismology
Authors: Christensen-Dalsgaard, J.
2013EAS....63...91C Altcode:
New observations of stellar pulsations, particularly from the CoRoT
and Kepler space missions, have opened completely new possibilities
for asteroseismic investigations for stars in large parts of
the Hertzsprung-Russell diagram. Particularly dramatic has been
the development of asteroseismology of stars showing solar-like
oscillations, where hundreds of stars near the main sequence and
tens of thousands of red giants can now be investigated. Although
the analysis of the data have yielded extensive information about
the global properties of the stars we are still only at the beginning
of learning how to use the data for more profound studies of stellar
interiors. Here I give a brief overview of the observations and discuss
the potential contributions to the understanding of stellar physics.
---------------------------------------------------------
Title: Stellar Spin-Orbit Misalignment in a Multiplanet System
Authors: Huber, Daniel; Carter, Joshua A.; Barbieri, Mauro; Miglio,
Andrea; Deck, Katherine M.; Fabrycky, Daniel C.; Montet, Benjamin T.;
Buchhave, Lars A.; Chaplin, William J.; Hekker, Saskia; Montalbán,
Josefina; Sanchis-Ojeda, Roberto; Basu, Sarbani; Bedding, Timothy R.;
Campante, Tiago L.; Christensen-Dalsgaard, Jørgen; Elsworth, Yvonne
P.; Stello, Dennis; Arentoft, Torben; Ford, Eric B.; Gilliland, Ronald
L.; Handberg, Rasmus; Howard, Andrew W.; Isaacson, Howard; Johnson,
John Asher; Karoff, Christoffer; Kawaler, Steven D.; Kjeldsen, Hans;
Latham, David W.; Lund, Mikkel N.; Lundkvist, Mia; Marcy, Geoffrey W.;
Metcalfe, Travis S.; Silva Aguirre, Victor; Winn, Joshua N.
2013Sci...342..331H Altcode: 2013arXiv1310.4503H
Stars hosting hot Jupiters are often observed to have high obliquities,
whereas stars with multiple coplanar planets have been seen to have low
obliquities. This has been interpreted as evidence that hot-Jupiter
formation is linked to dynamical disruption, as opposed to planet
migration through a protoplanetary disk. We used asteroseismology to
measure a large obliquity for Kepler-56, a red giant star hosting two
transiting coplanar planets. These observations show that spin-orbit
misalignments are not confined to hot-Jupiter systems. Misalignments
in a broader class of systems had been predicted as a consequence of
torques from wide-orbiting companions, and indeed radial velocity
measurements revealed a third companion in a wide orbit in the
Kepler-56 system.
---------------------------------------------------------
Title: Kepler White Paper: Asteroseismology of Solar-Like Oscillators
in a 2-Wheel Mission
Authors: Chaplin, W. J; Kjeldsen, H.; Christensen-Dalsgaard, J.;
Gilliland, R. L.; Kawaler, S. D.; Basu, S.; De Ridder, J.; Huber, D.;
Arentoft, T.; Schou, J.; Garcia, R. A.; Metcalfe, T. S.; Brogaard, K.;
Campante, T. L.; Elsworth, Y.; Miglio, A.; Appourchaux, T.; Bedding,
T. R.; Hekker, S.; Houdek, G.; Karoff, C.; Molenda-Zakowicz, J.;
Monteiro, M. J. P. F. G.; Silva Aguirre, V.; Stello, D.; Ball, W.;
Beck, P. G.; Birch, A. C.; Buzasi, D. L.; Casagrande, L.; Cellier,
T.; Corsaro, E.; Creevey, O. L.; Davies, G. R.; Deheuvels, S.; Dogan,
G.; Gizon, L.; Grundahl, F.; Guzik, J.; Handberg, R.; Jimenez, A.;
Kallinger, T.; Lund, M. N.; Lundkvist, M.; Mathis, S.; Mathur, S.;
Mazumdar, A.; Mosser, B.; Neiner, C.; Nielsen, M. B.; Palle, P. L.;
Pinsonneault, M. H.; Salabert, D.; Serenelli, A. M.; Shunker, H.;
White, T. R.
2013arXiv1309.0702C Altcode:
We comment on the potential for continuing asteroseismology of
solar-type and red-giant stars in a 2-wheel Kepler Mission. Our main
conclusion is that by targeting stars in the ecliptic it should be
possible to perform high-quality asteroseismology, as long as favorable
scenarios for 2-wheel pointing performance are met. Targeting the
ecliptic would potentially facilitate unique science that was not
possible in the nominal Mission, notably from the study of clusters
that are significantly brighter than those in the Kepler field. Our
conclusions are based on predictions of 2-wheel observations made by
a space photometry simulator, with information provided by the Kepler
Project used as input to describe the degraded pointing scenarios. We
find that elevated levels of frequency-dependent noise, consistent with
the above scenarios, would have a significant negative impact on our
ability to continue asteroseismic studies of solar-like oscillators in
the Kepler field. However, the situation may be much more optimistic
for observations in the ecliptic, provided that pointing resets of the
spacecraft during regular desaturations of the two functioning reaction
wheels are accurate at the < 1 arcsec level. This would make it
possible to apply a post-hoc analysis that would recover most of the
lost photometric precision. Without this post-hoc correction---and the
accurate re-pointing it requires---the performance would probably be
as poor as in the Kepler-field case. Critical to our conclusions for
both fields is the assumed level of pointing noise (in the short-term
jitter and the longer-term drift). We suggest that further tests will
be needed to clarify our results once more detail and data on the
expected pointing performance becomes available, and we offer our
assistance in this work.
---------------------------------------------------------
Title: Seismic study of solar convection and overshooting: results
of nonlocal convection
Authors: Zhang, Chun-Guang; Deng, Li-Cai; Xiong, Da-Run;
Christensen-Dalsgaard, Jørgen
2013RAA....13.1127Z Altcode: 2013arXiv1305.2085Z
Local mixing-length theory is incapable of describing nonlocal
phenomena in stellar convection, such as overshooting. Therefore
standard solar models constructed with local mixing-length theory
significantly deviate from the Sun at the boundariesof the convection
zone, where convection becomes less efficient and nonlocal effects are
important. The differences between observed and computed frequencies
mainly come from the region near the surface, while the localized
difference in sound speed is just below the convective envelope. We
compute a solar envelope model using Xiong's nonlocal convection
theory, and carry out helioseismic analysis. The nonlocal model has
a smooth transition at the base of the convection zone, as revealed
by helioseismology. It reproduces solar frequencies more accurately,
and reduces the localized difference in sound speed between the Sun
and standard solar models.
---------------------------------------------------------
Title: Sounding stellar cycles with Kepler - II. Ground-based
observations
Authors: Karoff, C.; Metcalfe, T. S.; Chaplin, W. J.; Frandsen, S.;
Grundahl, F.; Kjeldsen, H.; Christensen-Dalsgaard, J.; Nielsen, M. B.;
Frimann, S.; Thygesen, A. O.; Arentoft, T.; Amby, T. M.; Sousa, S. G.;
Buzasi, D. L.
2013MNRAS.433.3227K Altcode: 2013arXiv1306.3306K; 2013MNRAS.tmp.1612K
We have monitored 20 Sun-like stars in the Kepler field-of-view for
excess flux with the Fibre-fed Echelle Spectrograph on the Nordic
Optical Telescope since the launch of Kepler spacecraft in 2009. These
20 stars were selected based on their asteroseismic properties to
sample the parameter space (effective temperature, surface gravity,
activity level, etc.) around the Sun. Though the ultimate goal is
to improve stellar dynamo models, we focus the present paper on the
combination of space-based and ground-based observations that can
be used to test the age-rotation-activity relations. In this paper
we describe the considerations behind the selection of these 20
Sun-like stars and present an initial asteroseismic analysis, which
includes stellar age estimates. We also describe the observations
from the Nordic Optical Telescope and present mean values of measured
excess fluxes. These measurements are combined with estimates of the
rotation periods obtained from a simple analysis of the modulation
in photometric observations from Kepler caused by starspots, and
asteroseismic determinations of stellar ages, to test relations between
age, rotation and activity.
---------------------------------------------------------
Title: Astrophysics: Twinkling stars
Authors: Christensen-Dalsgaard, Jørgen
2013Natur.500..405C Altcode:
A correlation between stellar brightness variations and the
gravitational acceleration at a star's surface has been observed that
allows this acceleration to be measured with a precision of better
than 25%. See Letter p.427
---------------------------------------------------------
Title: Observations of the radial velocity of the Sun as measured
with the novel SONG spectrograph: results from a 1-week campaign
Authors: Pallé, P. L.; Grundahl, F.; Triviño Hage, A.;
Christensen-Dalsgaard, J.; Frandsen, S.; García, R. A.; Uytterhoeven,
K.; Andersen, M. F.; Rasmussen, P. K.; Sørensen, A. N.; Kjeldsen,
H.; Spano, P.; Nilsson, H.; Hartman, H.; Jørgensen, U. G.; Skottfelt,
J.; Harpsøe, K.; Andersen, M. I.
2013JPhCS.440a2051P Altcode:
Deployment of the prototype node of the SONG project took place in April
2012 at Observatorio del Teide (Canary Islands). Its key instrument
(echelle spectrograph) was installed and operational a few weeks later
while its 1 m feeding telescope suffered a considerable delay to meet
the required specifications. Using a fibre-feed, solar light could be
fed to the spectrograph and we carried out a 1-week observing campaign
in June 2012 to evaluate its performance for measuring precision
radial velocities. In this work we present the first results of this
campaign by comparing the sensitivity of the SONG spectrograph with
other helioseismology reference instruments (Mark-I and GOLF) when
simultaneous data are considered.
---------------------------------------------------------
Title: Stellar Ages and Convective Cores in Field Main-sequence Stars:
First Asteroseismic Application to Two Kepler Targets
Authors: Silva Aguirre, V.; Basu, S.; Brandão, I. M.;
Christensen-Dalsgaard, J.; Deheuvels, S.; Doğan, G.; Metcalfe, T. S.;
Serenelli, A. M.; Ballot, J.; Chaplin, W. J.; Cunha, M. S.; Weiss,
A.; Appourchaux, T.; Casagrande, L.; Cassisi, S.; Creevey, O. L.;
García, R. A.; Lebreton, Y.; Noels, A.; Sousa, S. G.; Stello, D.;
White, T. R.; Kawaler, S. D.; Kjeldsen, H.
2013ApJ...769..141S Altcode: 2013arXiv1304.2772S
Using asteroseismic data and stellar evolution models we obtain the
first detection of a convective core in a Kepler field main-sequence
star, putting a stringent constraint on the total size of the mixed
zone and showing that extra mixing beyond the formal convective
boundary exists. In a slightly less massive target the presence of
a convective core cannot be conclusively discarded, and thus its
remaining main-sequence lifetime is uncertain. Our results reveal
that best-fit models found solely by matching individual frequencies
of oscillations corrected for surface effects do not always properly
reproduce frequency combinations. Moreover, slightly different criteria
to define what the best-fit model is can lead to solutions with similar
global properties but very different interior structures. We argue that
the use of frequency ratios is a more reliable way to obtain accurate
stellar parameters, and show that our analysis in field main-sequence
stars can yield an overall precision of 1.5%, 4%, and 10% in radius,
mass, and age, respectively. We compare our results with those obtained
from global oscillation properties, and discuss the possible sources of
uncertainties in asteroseismic stellar modeling where further studies
are still needed.
---------------------------------------------------------
Title: Kepler-62: A Five-Planet System with Planets of 1.4 and 1.6
Earth Radii in the Habitable Zone
Authors: Borucki, William J.; Agol, Eric; Fressin, Francois;
Kaltenegger, Lisa; Rowe, Jason; Isaacson, Howard; Fischer, Debra;
Batalha, Natalie; Lissauer, Jack J.; Marcy, Geoffrey W.; Fabrycky,
Daniel; Désert, Jean-Michel; Bryson, Stephen T.; Barclay, Thomas;
Bastien, Fabienne; Boss, Alan; Brugamyer, Erik; Buchhave, Lars A.;
Burke, Chris; Caldwell, Douglas A.; Carter, Josh; Charbonneau, David;
Crepp, Justin R.; Christensen-Dalsgaard, Jørgen; Christiansen,
Jessie L.; Ciardi, David; Cochran, William D.; DeVore, Edna; Doyle,
Laurance; Dupree, Andrea K.; Endl, Michael; Everett, Mark E.; Ford,
Eric B.; Fortney, Jonathan; Gautier, Thomas N.; Geary, John C.; Gould,
Alan; Haas, Michael; Henze, Christopher; Howard, Andrew W.; Howell,
Steve B.; Huber, Daniel; Jenkins, Jon M.; Kjeldsen, Hans; Kolbl, Rea;
Kolodziejczak, Jeffery; Latham, David W.; Lee, Brian L.; Lopez, Eric;
Mullally, Fergal; Orosz, Jerome A.; Prsa, Andrej; Quintana, Elisa V.;
Sanchis-Ojeda, Roberto; Sasselov, Dimitar; Seader, Shawn; Shporer,
Avi; Steffen, Jason H.; Still, Martin; Tenenbaum, Peter; Thompson,
Susan E.; Torres, Guillermo; Twicken, Joseph D.; Welsh, William F.;
Winn, Joshua N.
2013Sci...340..587B Altcode: 2013arXiv1304.7387B
We present the detection of five planets—Kepler-62b, c, d,
e, and f—of size 1.31, 0.54, 1.95, 1.61 and 1.41 Earth radii
(R<SUB>⊕</SUB>), orbiting a K2V star at periods of 5.7, 12.4,
18.2, 122.4, and 267.3 days, respectively. The outermost planets,
Kepler-62e and -62f, are super-Earth-size (1.25 R<SUB>⊕</SUB> <
planet radius ≤ 2.0 R<SUB>⊕</SUB>) planets in the habitable zone
of their host star, respectively receiving 1.2 ± 0.2 times and 0.41
± 0.05 times the solar flux at Earth’s orbit. Theoretical models
of Kepler-62e and -62f for a stellar age of ~7 billion years suggest
that both planets could be solid, either with a rocky composition or
composed of mostly solid water in their bulk.
---------------------------------------------------------
Title: Erratum: A sub-Mercury-sized exoplanet
Authors: Barclay, Thomas; Rowe, Jason F.; Lissauer, Jack J.; Huber,
Daniel; Fressin, François; Howell, Steve B.; Bryson, Stephen
T.; Chaplin, William J.; Désert, Jean-Michel; Lopez, Eric D.;
Marcy, Geoffrey W.; Mullally, Fergal; Ragozzine, Darin; Torres,
Guillermo; Adams, Elisabeth R.; Agol, Eric; Barrado, David; Basu,
Sarbani; Bedding, Timothy R.; Buchhave, Lars A.; Charbonneau, David;
Christiansen, Jessie L.; Christensen-Dalsgaard, Jørgen; Ciardi, David;
Cochran, William D.; Dupree, Andrea K.; Elsworth, Yvonne; Everett,
Mark; Fischer, Debra A.; Ford, Eric B.; Fortney, Jonathan J.; Geary,
John C.; Haas, Michael R.; Handberg, Rasmus; Hekker, Saskia; Henze,
Christopher E.; Horch, Elliott; Howard, Andrew W.; Hunter, Roger C.;
Isaacson, Howard; Jenkins, Jon M.; Karoff, Christoffer; Kawaler,
Steven D.; Kjeldsen, Hans; Klaus, Todd C.; Latham, David W.; Li,
Jie; Lillo-Box, Jorge; Lund, Mikkel N.; Lundkvist, Mia; Metcalfe,
Travis S.; Miglio, Andrea; Morris, Robert L.; Quintana, Elisa V.;
Stello, Dennis; Smith, Jeffrey C.; Still, Martin; Thompson, Susan E.
2013Natur.496..252B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Fundamental Properties of Kepler Planet-candidate Host Stars
using Asteroseismology
Authors: Huber, Daniel; Chaplin, William J.; Christensen-Dalsgaard,
Jørgen; Gilliland, Ronald L.; Kjeldsen, Hans; Buchhave, Lars A.;
Fischer, Debra A.; Lissauer, Jack J.; Rowe, Jason F.; Sanchis-Ojeda,
Roberto; Basu, Sarbani; Handberg, Rasmus; Hekker, Saskia; Howard,
Andrew W.; Isaacson, Howard; Karoff, Christoffer; Latham, David W.;
Lund, Mikkel N.; Lundkvist, Mia; Marcy, Geoffrey W.; Miglio, Andrea;
Silva Aguirre, Victor; Stello, Dennis; Arentoft, Torben; Barclay,
Thomas; Bedding, Timothy R.; Burke, Christopher J.; Christiansen,
Jessie L.; Elsworth, Yvonne P.; Haas, Michael R.; Kawaler, Steven D.;
Metcalfe, Travis S.; Mullally, Fergal; Thompson, Susan E.
2013ApJ...767..127H Altcode: 2013arXiv1302.2624H
We have used asteroseismology to determine fundamental properties for
66 Kepler planet-candidate host stars, with typical uncertainties of
3% and 7% in radius and mass, respectively. The results include new
asteroseismic solutions for four host stars with confirmed planets
(Kepler-4, Kepler-14, Kepler-23 and Kepler-25) and increase the
total number of Kepler host stars with asteroseismic solutions to
77. A comparison with stellar properties in the planet-candidate
catalog by Batalha et al. shows that radii for subgiants and giants
obtained from spectroscopic follow-up are systematically too low by
up to a factor of 1.5, while the properties for unevolved stars are
in good agreement. We furthermore apply asteroseismology to confirm
that a large majority of cool main-sequence hosts are indeed dwarfs
and not misclassified giants. Using the revised stellar properties,
we recalculate the radii for 107 planet candidates in our sample, and
comment on candidates for which the radii change from a previously
giant-planet/brown-dwarf/stellar regime to a sub-Jupiter size or
vice versa. A comparison of stellar densities from asteroseismology
with densities derived from transit models in Batalha et al. assuming
circular orbits shows significant disagreement for more than half of
the sample due to systematics in the modeled impact parameters or
due to planet candidates that may be in eccentric orbits. Finally,
we investigate tentative correlations between host-star masses and
planet-candidate radii, orbital periods, and multiplicity, but caution
that these results may be influenced by the small sample size and
detection biases.
---------------------------------------------------------
Title: Properties of Oscillation Modes in Subgiant Stars Observed
by Kepler
Authors: Benomar, O.; Bedding, T. R.; Mosser, B.; Stello, D.;
Belkacem, K.; Garcia, R. A.; White, T. R.; Kuehn, C. A.; Deheuvels,
S.; Christensen-Dalsgaard, J.
2013ApJ...767..158B Altcode: 2013arXiv1302.4143B
Mixed modes seen in evolved stars carry information on their deeper
layers that can place stringent constraints on their physics and on
their global properties (mass, age, etc.). In this study, we present
a method to identify and measure all oscillatory mode characteristics
(frequency, height, width). Analyzing four subgiant stars, we present
the first measure of the effect of the degree of mixture on the l
= 1 mixed mode characteristics. We also show that some stars have
measurable l = 2 mixed modes and discuss the interest of their measure
to constrain the deeper layers of stars.
---------------------------------------------------------
Title: Asteroseismic Determination of Obliquities of the Exoplanet
Systems Kepler-50 and Kepler-65
Authors: Chaplin, W. J.; Sanchis-Ojeda, R.; Campante, T. L.; Handberg,
R.; Stello, D.; Winn, J. N.; Basu, S.; Christensen-Dalsgaard, J.;
Davies, G. R.; Metcalfe, T. S.; Buchhave, L. A.; Fischer, D. A.;
Bedding, T. R.; Cochran, W. D.; Elsworth, Y.; Gilliland, R. L.; Hekker,
S.; Huber, D.; Isaacson, H.; Karoff, C.; Kawaler, S. D.; Kjeldsen,
H.; Latham, D. W.; Lund, M. N.; Lundkvist, M.; Marcy, G. W.; Miglio,
A.; Barclay, T.; Lissauer, J. J.
2013ApJ...766..101C Altcode: 2013arXiv1302.3728C
Results on the obliquity of exoplanet host stars—the angle between
the stellar spin axis and the planetary orbital axis—provide important
diagnostic information for theories describing planetary formation. Here
we present the first application of asteroseismology to the problem
of stellar obliquity determination in systems with transiting planets
and Sun-like host stars. We consider two systems observed by the NASA
Kepler mission which have multiple transiting small (super-Earth sized)
planets: the previously reported Kepler-50 and a new system, Kepler-65,
whose planets we validate in this paper. Both stars show rich spectra
of solar-like oscillations. From the asteroseismic analysis we find
that each host has its rotation axis nearly perpendicular to the line
of sight with the sines of the angles constrained at the 1σ level to
lie above 0.97 and 0.91, respectively. We use statistical arguments to
show that coplanar orbits are favored in both systems, and that the
orientations of the planetary orbits and the stellar rotation axis
are correlated.
---------------------------------------------------------
Title: The High-latitude Branch of the Solar Torsional Oscillation
in the Rising Phase of Cycle 24
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R.;
Larson, T. P.; Rempel, M.; Schou, J.; Thompson, M. J.
2013ApJ...767L..20H Altcode:
We use global heliseismic data from the Global Oscillation Network
Group, the Michelson Doppler Imager on board the Solar and Heliospheric
Observatory, and the Helioseismic and Magnetic Imager on board the Solar
Dynamics Observatory, to examine the behavior, during the rising phase
of Solar Cycle 24, of the migrating zonal flow pattern known as the
torsional oscillation. Although the high-latitude part of the pattern
appears to be absent in the new cycle when the flows are derived by
subtracting a mean across a full solar cycle, it can be seen if we
subtract the mean over a shorter period in the rising phase of each
cycle, and these two mean rotation profiles differ significantly
at high latitudes. This indicates that the underlying high-latitude
rotation has changed; we speculate that this is in response to weaker
polar fields, as suggested by a recent model.
---------------------------------------------------------
Title: Kepler-68: Three Planets, One with a Density between that of
Earth and Ice Giants
Authors: Gilliland, Ronald L.; Marcy, Geoffrey W.; Rowe, Jason F.;
Rogers, Leslie; Torres, Guillermo; Fressin, Francois; Lopez, Eric
D.; Buchhave, Lars A.; Christensen-Dalsgaard, Jørgen; Désert,
Jean-Michel; Henze, Christopher E.; Isaacson, Howard; Jenkins,
Jon M.; Lissauer, Jack J.; Chaplin, William J.; Basu, Sarbani;
Metcalfe, Travis S.; Elsworth, Yvonne; Handberg, Rasmus; Hekker,
Saskia; Huber, Daniel; Karoff, Christoffer; Kjeldsen, Hans; Lund,
Mikkel N.; Lundkvist, Mia; Miglio, Andrea; Charbonneau, David; Ford,
Eric B.; Fortney, Jonathan J.; Haas, Michael R.; Howard, Andrew W.;
Howell, Steve B.; Ragozzine, Darin; Thompson, Susan E.
2013ApJ...766...40G Altcode: 2013arXiv1302.2596G
NASA's Kepler Mission has revealed two transiting planets orbiting
Kepler-68. Follow-up Doppler measurements have established the mass of
the innermost planet and revealed a third Jovian-mass planet orbiting
beyond the two transiting planets. Kepler-68b, in a 5.4 day orbit,
has M_P=8.3^{+2.2}_{-2.4} M <SUB>⊕</SUB>, R_P=2.31^{+0.06}_{-0.09}
R <SUB>⊕</SUB>, and \rho _P=3.32^{+0.86}_{-0.98} g cm<SUP>-3</SUP>,
giving Kepler-68b a density intermediate between that of the
ice giants and Earth. Kepler-68c is Earth-sized, with a radius
R_P=0.953^{+0.037}_{-0.042} R <SUB>⊕</SUB> and transits on a 9.6 day
orbit; validation of Kepler-68c posed unique challenges. Kepler-68d
has an orbital period of 580 ± 15 days and a minimum mass of M
<SUB>P</SUB>sin i = 0.947 ± 0.035M<SUB>J</SUB> . Power spectra of
the Kepler photometry at one minute cadence exhibit a rich and strong
set of asteroseismic pulsation modes enabling detailed analysis of the
stellar interior. Spectroscopy of the star coupled with asteroseismic
modeling of the multiple pulsation modes yield precise measurements
of stellar properties, notably T <SUB>eff</SUB> = 5793 ± 74 K, M
<SUB>sstarf</SUB> = 1.079 ± 0.051 M <SUB>⊙</SUB>, R <SUB>sstarf</SUB>
= 1.243 ± 0.019 R <SUB>⊙</SUB>, and ρ<SUB>sstarf</SUB> = 0.7903 ±
0.0054 g cm<SUP>-3</SUP>, all measured with fractional uncertainties
of only a few percent. Models of Kepler-68b suggest that it is likely
composed of rock and water, or has a H and He envelope to yield its
density ~3 g cm<SUP>-3</SUP>.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Kepler planetary
candidates. III. (Batalha+, 2013)
Authors: Batalha, N. M.; Rowe, J. F.; Bryson, S. T.; Barclay, T.;
Burke, C. J.; Caldwell, D. A.; Christiansen, J. L.; Mullally, F.;
Thompson, S. E.; Brown, T. M.; Dupree, A. K.; Fabrycky, D. C.; Ford,
E. B.; Fortney, J. J.; Gilliland, R. L.; Isaacson, H.; Latham,
D. W.; Marcy, G. W.; Quinn, S. N.; Ragozzine, D.; Shporer, A.;
Borucki, W. J.; Ciardi, D. R.; Gautier, T. N., III; Haas, M. R.;
Jenkins, J. M.; Koch, D. G.; Lissauer, J. J.; Rapin, W.; Basri,
G. S.; Boss, A. P.; Buchhave, L. A.; Carter, J. A.; Charbonneau, D.;
Christensen-Dalsgaard, J.; Clarke, B. D.; Cochran, W. D.; Demory,
B. -O.; Desert, J. -M.; DeVore, E.; Doyle, L. R.; Esquerdo, G. A.;
Everett, M.; Fressin, F.; Geary, J. C.; Girouard, F. R.; Gould, A.;
Hall, J. R.; Holman, M. J.; Howard, A. W.; Howell, S. B.; Ibrahim,
K. A.; Kinemuchi, K.; Kjeldsen, H.; Klaus, T. C.; Li, J.; Lucas,
P. W.; Meibom, S.; Morris, R. L.; Prsa, A.; Quintana, E.; Sanderfer,
D. T.; Sasselov, D.; Seader, S. E.; Smith, J. C.; Steffen, J. H.;
Still, M.; Stumpe, M. C.; Tarter, J. C.; Tenenbaum, P.; Torres, G.;
Twicken, J. D.; Uddin, K.; van Cleve, J.; Walkowicz, L.; Welsh, W. F.
2013yCat..22040024B Altcode:
The data employed for transit identification were acquired between 2009
May 13 00:15 UTC and 2010 Sep 22 19:03 UTC (Q1-Q6). Over 190000 stars
were observed at some time during this period. <P />(6 data files).
---------------------------------------------------------
Title: Internal rotation of red giants by asteroseismology
Authors: Di Mauro, M. P.; Cardini, D.; Ventura, R.; Stello, D.; Beck,
P. G.; Davies, G.; Elsworth, Y.; García, R. A.; Hekker, S.; Mosser,
B.; Christensen-Dalsgaard, J.; Bloemen, S.; Catanzaro, G.; De Smedt,
K.; Tkachenko, A.
2013EPJWC..4303012D Altcode: 2012arXiv1212.4758D
We present an asteroseismic approach to study the dynamics of the
stellar interior in red giant stars by asteroseismic inversion of
the splittings induced by the stellar rotation on the oscillation
frequencies. We show preliminary results obtained for the red giant
KIC4448777 observed by the space mission Kepler.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Abundances of 93 solar-type Kepler
targets (Bruntt+, 2012)
Authors: Bruntt, H.; Basu, S.; Smalley, B.; Chaplin, W. J.; Verner,
G. A.; Bedding, T. R.; Catala, C.; Gazzano, J. -C.; Molenda-Zakowicz,
J.; Thygesen, A. O.; Uytterhoeven, K.; Hekker, S.; Huber, D.; Karoff,
C.; Mathur, S.; Mosser, B.; Appourchaux, T.; Campante, T. L.; Elsworth,
Y.; Garcia, R. A.; Handberg, R.; Metcalfe, T. S.; Quirion, P. -O.;
Regulo, C.; Roxburgh, I. W.; Stello, D.; Christensen-Dalsgaard,
J.; Kawaler, S. D.; Kjeldsen, H.; Morris, R. L.; Quintana, E. V.;
Sanderfer, D. T.
2013yCat..74230122B Altcode:
The spectra were obtained with the ESPaDOnS spectrograph at the 3.6-m
Canada-France-Hawaii Telescope (CFHT) in USA and with the NARVAL
spectrograph mounted on the 2-m Bernard Lyot Telescope at the Pic du
Midi Observatory in France. In both the facilities, the observations
were carried out as service observations from May to September in
2010. <P />(3 data files).
---------------------------------------------------------
Title: A sub-Mercury-sized exoplanet
Authors: Barclay, Thomas; Rowe, Jason F.; Lissauer, Jack J.; Huber,
Daniel; Fressin, François; Howell, Steve B.; Bryson, Stephen
T.; Chaplin, William J.; Désert, Jean-Michel; Lopez, Eric D.;
Marcy, Geoffrey W.; Mullally, Fergal; Ragozzine, Darin; Torres,
Guillermo; Adams, Elisabeth R.; Agol, Eric; Barrado, David; Basu,
Sarbani; Bedding, Timothy R.; Buchhave, Lars A.; Charbonneau, David;
Christiansen, Jessie L.; Christensen-Dalsgaard, Jørgen; Ciardi, David;
Cochran, William D.; Dupree, Andrea K.; Elsworth, Yvonne; Everett,
Mark; Fischer, Debra A.; Ford, Eric B.; Fortney, Jonathan J.; Geary,
John C.; Haas, Michael R.; Handberg, Rasmus; Hekker, Saskia; Henze,
Christopher E.; Horch, Elliott; Howard, Andrew W.; Hunter, Roger C.;
Isaacson, Howard; Jenkins, Jon M.; Karoff, Christoffer; Kawaler,
Steven D.; Kjeldsen, Hans; Klaus, Todd C.; Latham, David W.; Li,
Jie; Lillo-Box, Jorge; Lund, Mikkel N.; Lundkvist, Mia; Metcalfe,
Travis S.; Miglio, Andrea; Morris, Robert L.; Quintana, Elisa V.;
Stello, Dennis; Smith, Jeffrey C.; Still, Martin; Thompson, Susan E.
2013Natur.494..452B Altcode: 2013arXiv1305.5587B
Since the discovery of the first exoplanets, it has been known that
other planetary systems can look quite unlike our own. Until fairly
recently, we have been able to probe only the upper range of the planet
size distribution, and, since last year, to detect planets that are
the size of Earth or somewhat smaller. Hitherto, no planets have been
found that are smaller than those we see in the Solar System. Here we
report a planet significantly smaller than Mercury. This tiny planet
is the innermost of three that orbit the Sun-like host star, which we
have designated Kepler-37. Owing to its extremely small size, similar to
that of the Moon, and highly irradiated surface, the planet, Kepler-37b,
is probably rocky with no atmosphere or water, similar to Mercury.
---------------------------------------------------------
Title: Planetary Candidates Observed by Kepler. III. Analysis of
the First 16 Months of Data
Authors: Batalha, Natalie M.; Rowe, Jason F.; Bryson, Stephen
T.; Barclay, Thomas; Burke, Christopher J.; Caldwell, Douglas A.;
Christiansen, Jessie L.; Mullally, Fergal; Thompson, Susan E.; Brown,
Timothy M.; Dupree, Andrea K.; Fabrycky, Daniel C.; Ford, Eric B.;
Fortney, Jonathan J.; Gilliland, Ronald L.; Isaacson, Howard; Latham,
David W.; Marcy, Geoffrey W.; Quinn, Samuel N.; Ragozzine, Darin;
Shporer, Avi; Borucki, William J.; Ciardi, David R.; Gautier, Thomas
N., III; Haas, Michael R.; Jenkins, Jon M.; Koch, David G.; Lissauer,
Jack J.; Rapin, William; Basri, Gibor S.; Boss, Alan P.; Buchhave,
Lars A.; Carter, Joshua A.; Charbonneau, David; Christensen-Dalsgaard,
Joergen; Clarke, Bruce D.; Cochran, William D.; Demory, Brice-Olivier;
Desert, Jean-Michel; Devore, Edna; Doyle, Laurance R.; Esquerdo,
Gilbert A.; Everett, Mark; Fressin, Francois; Geary, John C.; Girouard,
Forrest R.; Gould, Alan; Hall, Jennifer R.; Holman, Matthew J.; Howard,
Andrew W.; Howell, Steve B.; Ibrahim, Khadeejah A.; Kinemuchi, Karen;
Kjeldsen, Hans; Klaus, Todd C.; Li, Jie; Lucas, Philip W.; Meibom,
Søren; Morris, Robert L.; Prša, Andrej; Quintana, Elisa; Sanderfer,
Dwight T.; Sasselov, Dimitar; Seader, Shawn E.; Smith, Jeffrey C.;
Steffen, Jason H.; Still, Martin; Stumpe, Martin C.; Tarter, Jill C.;
Tenenbaum, Peter; Torres, Guillermo; Twicken, Joseph D.; Uddin, Kamal;
Van Cleve, Jeffrey; Walkowicz, Lucianne; Welsh, William F.
2013ApJS..204...24B Altcode: 2012arXiv1202.5852B
New transiting planet candidates are identified in 16 months (2009
May-2010 September) of data from the Kepler spacecraft. Nearly 5000
periodic transit-like signals are vetted against astrophysical and
instrumental false positives yielding 1108 viable new planet candidates,
bringing the total count up to over 2300. Improved vetting metrics
are employed, contributing to higher catalog reliability. Most notable
is the noise-weighted robust averaging of multi-quarter photo-center
offsets derived from difference image analysis that identifies likely
background eclipsing binaries. Twenty-two months of photometry are used
for the purpose of characterizing each of the candidates. Ephemerides
(transit epoch, T <SUB>0</SUB>, and orbital period, P) are tabulated
as well as the products of light curve modeling: reduced radius
(R <SUB>P</SUB>/R <SUB>sstarf</SUB>), reduced semimajor axis (d/R
<SUB>sstarf</SUB>), and impact parameter (b). The largest fractional
increases are seen for the smallest planet candidates (201% for
candidates smaller than 2 R <SUB>⊕</SUB> compared to 53% for
candidates larger than 2 R <SUB>⊕</SUB>) and those at longer orbital
periods (124% for candidates outside of 50 day orbits versus 86% for
candidates inside of 50 day orbits). The gains are larger than expected
from increasing the observing window from 13 months (Quarters 1-5)
to 16 months (Quarters 1-6) even in regions of parameter space where
one would have expected the previous catalogs to be complete. Analyses
of planet frequencies based on previous catalogs will be affected by
such incompleteness. The fraction of all planet candidate host stars
with multiple candidates has grown from 17% to 20%, and the paucity of
short-period giant planets in multiple systems is still evident. The
progression toward smaller planets at longer orbital periods with each
new catalog release suggests that Earth-size planets in the habitable
zone are forthcoming if, indeed, such planets are abundant.
---------------------------------------------------------
Title: Stellar Pulsations
Authors: Suárez, J. C.; Garrido, R.; Balona, L. A.;
Christensen-Dalsgaard, J.
2013ASSP...31.....S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: List of Poster Contributions
Authors: Suárez, J. C.; Garrido, R.; Balona, L. A.;
Christensen-Dalsgaard, J.
2013ASSP...31..291S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Characterizing Two Solar-type Kepler Subgiants with
Asteroseismology: KIC 10920273 and KIC 11395018
Authors: Doǧan, G.; Metcalfe, T. S.; Deheuvels, S.; Di Mauro,
M. P.; Eggenberger, P.; Creevey, O. L.; Monteiro, M. J. P. F. G.;
Pinsonneault, M.; Frasca, A.; Karoff, C.; Mathur, S.; Sousa, S. G.;
Brandão, I. M.; Campante, T. L.; Handberg, R.; Thygesen, A. O.;
Biazzo, K.; Bruntt, H.; Niemczura, E.; Bedding, T. R.; Chaplin, W. J.;
Christensen-Dalsgaard, J.; García, R. A.; Molenda-Żakowicz, J.;
Stello, D.; Van Saders, J. L.; Kjeldsen, H.; Still, M.; Thompson,
S. E.; Van Cleve, J.
2013ApJ...763...49D Altcode: 2012arXiv1211.6650D
Determining fundamental properties of stars through stellar
modeling has improved substantially due to recent advances in
asteroseismology. Thanks to the unprecedented data quality obtained by
space missions, particularly CoRoT and Kepler, invaluable information
is extracted from the high-precision stellar oscillation frequencies,
which provide very strong constraints on possible stellar models for a
given set of classical observations. In this work, we have characterized
two relatively faint stars, KIC 10920273 and KIC 11395018, using
oscillation data from Kepler photometry and atmospheric constraints from
ground-based spectroscopy. Both stars have very similar atmospheric
properties; however, using the individual frequencies extracted from
the Kepler data, we have determined quite distinct global properties,
with increased precision compared to that of earlier results. We found
that both stars have left the main sequence and characterized them
as follows: KIC 10920273 is a one-solar-mass star (M = 1.00 ± 0.04 M
<SUB>⊙</SUB>), but much older than our Sun (t = 7.12 ± 0.47 Gyr),
while KIC 11395018 is significantly more massive than the Sun (M =
1.27 ± 0.04 M <SUB>⊙</SUB>) with an age close to that of the Sun
(t = 4.57 ± 0.23 Gyr). We confirm that the high lithium abundance
reported for these stars should not be considered to represent young
ages, as we precisely determined them to be evolved subgiants. We
discuss the use of surface lithium abundance, rotation, and activity
relations as potential age diagnostics.
---------------------------------------------------------
Title: Asteroseismology with NASA's Kepler Mission
Authors: Huber, Daniel; Chaplin, W. J.; Christensen-Dalsgaard, J.;
Gilliland, R. L.; Kawaler, S. D.; Kjeldsen, H.; Working Groups of
Kepler Asteroseismic Science Consortium (KASC)
2013AAS...22130101H Altcode:
The measurement of stellar oscillations - also called asteroseismology -
is among the most powerful observational tools to study the structure
and evolution of stars. The high precision photometry collected by the
Kepler space telescope has revolutionized asteroseismology over the past
few years by boosting the number of stars with detected oscillations by
nearly two orders of magnitude over ground-based efforts, and delivering
data with unprecedented signal-to-noise. In this talk I will highlight
some of the recent breakthrough discoveries by the Kepler Mission,
focusing in particular on the internal composition and rotation of red
giants and the study of fundamental properties in large ensembles of
stars throughout the Hertzsprung-Russell diagram. I will furthermore
present results for an ensemble of ~80 Kepler Objects of Interest for
which accurate host star and planet candidate properties have been
determined using asteroseismology.
---------------------------------------------------------
Title: Red giant oscillations: Stellar models and mode frequency
calculations
Authors: Jendreieck, A.; Weiss, A.; Silva Aguirre, V.;
Christensen-Dalsgaard, J.; Handberg, R.; Ruchti, G.; Jiang, C.;
Thygesen, A.
2012AN....333..939J Altcode: 2012arXiv1210.6495J
We present preliminary results on modelling KIC 7693833, the so far most
metal-poor red giant star observed by Kepler. From time series spanning
several months, global oscillation parameters and individual frequencies
were obtained and compared to theoretical calculations. Evolution models
are calculated taking into account spectroscopic and asteroseismic
constraints. The oscillation frequencies of the models were computed
and compared to the Kepler data. In the range of mass computed,
there is no preferred model, giving an uncertainty of about 30 K in
T<SUB>eff</SUB>, 0.02 dex in log g, 0.7R<SUB>⊙</SUB> in radius,
and of about 2.5 Gyrs in age.
---------------------------------------------------------
Title: Properties of extrasolar planets and their host stars: A case
study of HAT-P-7
Authors: Van Eylen, V.; Kjeldsen, H.; Christensen-Dalsgaard, J.;
Aerts, C.
2012AN....333.1088V Altcode: 2013arXiv1301.1472V
Data from the Kepler satellite (Q0-Q11) are used to study HAT-P-7. The
satellite's data are extremely valuable for asteroseismic studies of
stars and for observing planetary transits; in this work we do both. An
asteroseismic study of the host star improves the accuracy of the
stellar parameters derived by Christensen-Dalsgaard et al. (2010), who
followed largely the same procedure but based the analysis on only one
month of Kepler data. The stellar information is combined with transit
observations, phase variations and occultations to derive planetary
parameters. In particular, we confirm the presence of ellipsoidal
variations as discovered by Welsh et al. (2010), but revise their
magnitude, and we revise the occultation depth (Borucki et al. 2009)
which leads to different planetary temperature estimates. All other
stellar and planetary parameters are now more accurately determined.
---------------------------------------------------------
Title: A Bayesian approach to the modelling of α Cen A
Authors: Bazot, M.; Bourguignon, S.; Christensen-Dalsgaard, J.
2012MNRAS.427.1847B Altcode: 2012arXiv1209.0222B
Determining the physical characteristics of a star is an inverse problem
consisting of estimating the parameters of models for the stellar
structure and evolution, and knowing certain observable quantities. We
use a Bayesian approach to solve this problem for α Cen A, which allows
us to incorporate prior information on the parameters to be estimated,
in order to better constrain the problem. Our strategy is based on
the use of a Markov chain Monte Carlo (MCMC) algorithm to estimate
the posterior probability densities of the stellar parameters: mass,
age, initial chemical composition, etc. We use the stellar evolutionary
code ASTEC to model the star. To constrain this model both seismic and
non-seismic observations were considered. Several different strategies
were tested to fit these values, using either two free parameters
or five free parameters in ASTEC. We are thus able to show evidence
that MCMC methods become efficient with respect to more classical
grid-based strategies when the number of parameters increases. The
results of our MCMC algorithm allow us to derive estimates for the
stellar parameters and robust uncertainties thanks to the statistical
analysis of the posterior probability densities. We are also able to
compute odds for the presence of a convective core in α Cen A. When
using core-sensitive seismic observational constraints, these can rise
above ∼40 per cent. The comparison of results to previous studies
also indicates that these seismic constraints are of critical importance
for our knowledge of the structure of this star.
---------------------------------------------------------
Title: SONG-OT: The prototype SONG node at Tenerife
Authors: Uytterhoeven, K.; Pallé, P. L.; Grundahl, F.; Frandsen,
S.; Christensen-Dalsgaard, J.; Triviño Hage, A.; SONG Team
2012AN....333.1103U Altcode:
The prototype SONG node, SONG-OT, is currently being installed and
tested at Observatory del Teide on Tenerife. SONG will be a global
network of 1-m robotic telescopes, equipped with a high-resolution
échelle spectrograph and dual-colour lucky imaging cameras. The
network will be devoted to the seismic study of bright stars and
characterisation of low-mass planets. We present the current status
of the network in general and the SONG-OT node in particular.
---------------------------------------------------------
Title: Stellar model fits and inversions
Authors: Christensen-Dalsgaard, J.
2012AN....333..914C Altcode: 2012arXiv1211.2697C
The recent asteroseismic data from the CoRoT and Kepler missions
have provided an entirely new basis for investigating stellar
properties. This has led to a rapid development in techniques for
analysing such data, although it is probably fair to say that we
are still far from having the tools required for the full use of the
potential of the observations. Here I provide a brief overview of some
of the issues related to the interpretation of asteroseismic data.
---------------------------------------------------------
Title: Acoustic glitches in solar-type stars from Kepler
Authors: Mazumdar, A.; Monteiro, M. J. P. F. G.; Ballot, J.; Antia,
H. M.; Basu, S.; Houdek, G.; Mathur, S.; Cunha, M. S.; Silva Aguirre,
V.; García, R. A.; Salabert, D.; Verner, G. A.; Christensen-Dalsgaard,
J.; Metcalfe, T. S.; Chaplin, W. J.
2012AN....333.1040M Altcode:
We report the measurement of the acoustic locations of layers of
sharp variation in sound speed in the interiors of 19 solar-type
stars observed by the Kepler mission. The oscillatory signal in the
frequencies arising due to the acoustic glitches at the base of the
convection zone and the second helium ionisation zone was utilised
to determine their location by four independent methods. Despite the
significantly different methods of analysis, remarkable agreement
was found between the results of these four methods. Further, the
extracted locations of these layers were found to be consistent with
representative models of the stars.
---------------------------------------------------------
Title: Fundamental Properties of Stars Using Asteroseismology from
Kepler and CoRoT and Interferometry from the CHARA Array
Authors: Huber, D.; Ireland, M. J.; Bedding, T. R.; Brandão, I. M.;
Piau, L.; Maestro, V.; White, T. R.; Bruntt, H.; Casagrande, L.;
Molenda-Żakowicz, J.; Silva Aguirre, V.; Sousa, S. G.; Barclay,
T.; Burke, C. J.; Chaplin, W. J.; Christensen-Dalsgaard, J.; Cunha,
M. S.; De Ridder, J.; Farrington, C. D.; Frasca, A.; García, R. A.;
Gilliland, R. L.; Goldfinger, P. J.; Hekker, S.; Kawaler, S. D.;
Kjeldsen, H.; McAlister, H. A.; Metcalfe, T. S.; Miglio, A.; Monteiro,
M. J. P. F. G.; Pinsonneault, M. H.; Schaefer, G. H.; Stello, D.;
Stumpe, M. C.; Sturmann, J.; Sturmann, L.; ten Brummelaar, T. A.;
Thompson, M. J.; Turner, N.; Uytterhoeven, K.
2012ApJ...760...32H Altcode: 2012arXiv1210.0012H
We present results of a long-baseline interferometry campaign using
the PAVO beam combiner at the CHARA Array to measure the angular
sizes of five main-sequence stars, one subgiant and four red
giant stars for which solar-like oscillations have been detected
by either Kepler or CoRoT. By combining interferometric angular
diameters, Hipparcos parallaxes, asteroseismic densities, bolometric
fluxes, and high-resolution spectroscopy, we derive a full set of
near-model-independent fundamental properties for the sample. We
first use these properties to test asteroseismic scaling relations
for the frequency of maximum power (ν<SUB>max</SUB>) and the large
frequency separation (Δν). We find excellent agreement within the
observational uncertainties, and empirically show that simple estimates
of asteroseismic radii for main-sequence stars are accurate to <~
4%. We furthermore find good agreement of our measured effective
temperatures with spectroscopic and photometric estimates with mean
deviations for stars between T <SUB>eff</SUB> = 4600-6200 K of -22 ±
32 K (with a scatter of 97 K) and -58 ± 31 K (with a scatter of 93 K),
respectively. Finally, we present a first comparison with evolutionary
models, and find differences between observed and theoretical properties
for the metal-rich main-sequence star HD 173701. We conclude that
the constraints presented in this study will have strong potential
for testing stellar model physics, in particular when combined with
detailed modeling of individual oscillation frequencies.
---------------------------------------------------------
Title: Sound-speed Inversion of the Sun Using a Nonlocal Statistical
Convection Theory
Authors: Zhang, Chunguang; Deng, Licai; Xiong, Darun;
Christensen-Dalsgaard, Jørgen
2012ApJ...759L..14Z Altcode: 2012arXiv1210.4286Z
Helioseismic inversions reveal a major discrepancy in sound speed
between the Sun and the standard solar model just below the base
of the solar convection zone. We demonstrate that this discrepancy
is caused by the inherent shortcomings of the local mixing-length
theory adopted in the standard solar model. Using a self-consistent
nonlocal convection theory, we construct an envelope model of the
Sun for sound-speed inversion. Our solar model has a very smooth
transition from the convective envelope to the radiative interior,
and the convective energy flux changes sign crossing the boundaries
of the convection zone. It shows evident improvement over the standard
solar model, with a significant reduction in the discrepancy in sound
speed between the Sun and local convection models.
---------------------------------------------------------
Title: Asteroseismology of the Open Clusters NGC 6791, NGC 6811,
and NGC 6819 from 19 Months of Kepler Photometry
Authors: Corsaro, Enrico; Stello, Dennis; Huber, Daniel; Bedding,
Timothy R.; Bonanno, Alfio; Brogaard, Karsten; Kallinger, Thomas;
Benomar, Othman; White, Timothy R.; Mosser, Benoit; Basu, Sarbani;
Chaplin, William J.; Christensen-Dalsgaard, Jørgen; Elsworth, Yvonne
P.; García, Rafael A.; Hekker, Saskia; Kjeldsen, Hans; Mathur,
Savita; Meibom, Søren; Hall, Jennifer R.; Ibrahim, Khadeejah A.;
Klaus, Todd C.
2012ApJ...757..190C Altcode: 2012arXiv1205.4023C
We studied solar-like oscillations in 115 red giants in the three open
clusters, NGC 6791, NGC 6811, and NGC 6819, based on photometric data
covering more than 19 months with NASA's Kepler space telescope. We
present the asteroseismic diagrams of the asymptotic parameters
δν<SUB>02</SUB>, δν<SUB>01</SUB>, and epsilon, which show clear
correlation with fundamental stellar parameters such as mass and
radius. When the stellar populations from the clusters are compared,
we see evidence for a difference in mass of the red giant branch
stars and possibly a difference in structure of the red clump stars,
from our measurements of the small separations δν<SUB>02</SUB> and
δν<SUB>01</SUB>. Ensemble échelle diagrams and upper limits to the
linewidths of l = 0 modes as a function of Δν of the clusters NGC
6791 and NGC 6819 are also shown, together with the correlation between
the l = 0 ridge width and the T <SUB>eff</SUB> of the stars. Lastly,
we distinguish between red giant branch and red clump stars through
the measurement of the period spacing of mixed dipole modes in 53 stars
among all the three clusters to verify the stellar classification from
the color-magnitude diagram. These seismic results also allow us to
identify a number of special cases, including evolved blue stragglers
and binaries, as well as stars in late He-core burning phases, which can
be potentially interesting targets for detailed theoretical modeling.
---------------------------------------------------------
Title: Kepler Asteroseismology of Red-giant Stars
Authors: Christensen-Dalsgaard, J.
2012ASPC..462..503C Altcode: 2011arXiv1110.5012C
The Kepler mission, launched in March 2009, has revolutionized
asteroseismology, providing detailed observations of thousands of
stars. This has allowed in-depth analyses of stars ranging from compact
hot subdwarfs to red giants, and including the detection of solar-like
oscillations in hundreds of stars on or near the main sequence. Here
I mainly consider solar-like oscillations in red giants, where Kepler
observations are yielding results of a perhaps unexpected richness. In
addition to giving a brief overview of the observational and numerical
results for these stars, I present a simple analysis which captures
some of the properties of the observed frequencies.
---------------------------------------------------------
Title: The First Evidence for Multiple Pulsation Axes: A New roAp
Star in the Kepler Field, KIC 10195926
Authors: Kurtz, D. W.; Cunha, M. S.; Saio, H.; Bigot, L.; Balona,
L. A.; Elkin, V. G.; Shibahashi, H.; Brandão, I. M.; Uytterhoeven,
K. : Frandsen, S.; Frimann, S.; Hatzes, A.; Lueftinger, T.;
Gruberbauer, M.; Kjeldsen, H.; Christensen-Dalsgaard, J.; Kawaler,
S. D.
2012ASPC..462..125K Altcode:
This conference talk introduced the characteristics of the rapidly
oscillating Ap stars, then discussed a new rapidly oscillating Ap star
discovered and published by Working Group 5 of the Kepler Asteroseismic
Science Consortium, KIC 10195926. This star shows two pulsation modes
with periods that are amongst the longest known for roAp stars at 17.1
min and 18.1 min, indicating that the star is near the terminal-age
main-sequence. The principal pulsation mode is an oblique dipole
mode that shows a rotationally split frequency septuplet that provides
information on the geometry of the mode. The secondary mode also appears
to be a dipole mode with a rotationally split triplet, but within the
improved oblique pulsator model these two modes cannot have the same
axis of pulsation. This is the first time for any pulsating star that
evidence has been found for separate pulsation axes for different modes.
---------------------------------------------------------
Title: Verifying Asteroseismically Determined Parameters of Kepler
Stars Using Hipparcos Parallaxes: Self-consistent Stellar Properties
and Distances
Authors: Silva Aguirre, V.; Casagrande, L.; Basu, S.; Campante, T. L.;
Chaplin, W. J.; Huber, D.; Miglio, A.; Serenelli, A. M.; Ballot, J.;
Bedding, T. R.; Christensen-Dalsgaard, J.; Creevey, O. L.; Elsworth,
Y.; García, R. A.; Gilliland, R. L.; Hekker, S.; Kjeldsen, H.;
Mathur, S.; Metcalfe, T. S.; Monteiro, M. J. P. F. G.; Mosser, B.;
Pinsonneault, M. H.; Stello, D.; Weiss, A.; Tenenbaum, P.; Twicken,
J. D.; Uddin, K.
2012ApJ...757...99S Altcode: 2012arXiv1208.6294S
Accurately determining the properties of stars is of prime importance
for characterizing stellar populations in our Galaxy. The field of
asteroseismology has been thought to be particularly successful in
such an endeavor for stars in different evolutionary stages. However,
to fully exploit its potential, robust methods for estimating stellar
parameters are required and independent verification of the results
is mandatory. With this purpose, we present a new technique to obtain
stellar properties by coupling asteroseismic analysis with the InfraRed
Flux Method. By using two global seismic observables and multi-band
photometry, the technique allows us to obtain masses, radii, effective
temperatures, bolometric fluxes, and hence distances for field stars
in a self-consistent manner. We apply our method to 22 solar-like
oscillators in the Kepler short-cadence sample, that have accurate
Hipparcos parallaxes. Our distance determinations agree to better than
5%, while measurements of spectroscopic effective temperatures and
interferometric radii also validate our results. We briefly discuss
the potential of our technique for stellar population analysis and
models of Galactic Chemical Evolution.
---------------------------------------------------------
Title: Fast Rotating Solar-like Stars Using Asteroseismic Datasets
Authors: García, R. A.; Ceillier, T.; Campante, T. L.; Davies, G. R.;
Mathur, S.; Suárez, J. C.; Ballot, J.; Benomar, O.; Bonanno, A.;
Brun, A. S.; Chaplin, W. J.; Christensen-Dalsgaard, J.; Deheuvels,
S.; Elsworth, Y.; Handberg, R.; Hekker, S.; Jiménez, A.; Karoff, C.;
Kjeldsen, H.; Mathis, S.; Mosser, B.; Pallé, P. L.; Pinsonneault, M.;
Régulo, C.; Salabert, D.; Silva Aguirre, V.; Stello, D.; Thompson,
M. J.; Verner, G.; PE11 Team of Kepler WG#1
2012ASPC..462..133G Altcode: 2011arXiv1109.6488G
The NASA Kepler mission is providing an unprecedented set of
asteroseismic data. In particular, short-cadence light-curves (∼ 60
s samplings), allow us to study solar-like stars covering a wide range
of masses, spectral types and evolutionary stages. Oscillations have
been observed in around 600 out of 2000 stars observed for one month
during the survey phase of the Kepler mission. The measured light
curves can present features related to the surface magnetic activity
(starspots) and, thus we are able to obtain a good estimate of the
surface (differential) rotation. In this work we establish the basis
of such research and we show a potential method to find stars with
fast surface rotation.
---------------------------------------------------------
Title: Seismic Analysis of Four Solar-like Stars Observed during
More Than Eight Months by Kepler
Authors: Mathur, S.; Campante, T. L.; Handberg, R.; García, R. A.;
Appourchaux, T.; Bedding, T. R.; Mosser, B.; Chaplin, W. J.; Ballot,
J.; Benomar, O.; Bonanno, A.; Corsaro, E.; Gaulme, P.; Hekker,
S.; Régulo, C.; Salabert, D.; Verner, G.; White, T. R.; Brandão,
I. M.; Creevey, O. L.; Dogan, G.; Bazot, M.; Cunha, M. S.; Elsworth,
Y.; Huber, D.; Hale, S. J.; Houdek, G.; Karoff, C.; Lundkvist, M.;
Metcalfe, T. S.; Molenda-Zakowicz, J.; Monteiro, M. J. P. F. G.;
Thompson, M. J.; Stello, D.; Christensen-Dalsgaard, J.; Gilliland,
R. L.; Kawaler, S. D.; Kjeldsen, H.; Clarke, B. D.; Girouard, F. R.;
Hall, J. R.; Quintana, E. V.; Sanderfer, D. T.; Seader, S. E.
2012ASPC..462..180M Altcode: 2011arXiv1110.0135M
Having started science operations in May 2009, the Kepler photometer
has been able to provide exquisite data for solar-like stars. Five
out of the 42 stars observed continuously during the survey phase
show evidence of oscillations, even though they are rather faint
(magnitudes from 10.5 to 12). In this paper, we present an overview
of the results of the seismic analysis of 4 of these stars observed
during more than eight months.
---------------------------------------------------------
Title: Detailed Study of the Internal Structure of a Red-giant Star
Observed with Kepler
Authors: Di Mauro, M. P.; Ventura, R.; Cardini, D.; Catanzaro, G.;
Barban, C.; Bedding, T. R.; Christensen-Dalsgaard, J.; De Ridder,
J.; Hekker, S.; Huber, D.; Kallinger, T.; Kinemuchi, K.; Kjeldsen,
H.; Miglio, A.; Montalbán, J.; Mosser, B.; Mullally, F.; Stello,
D.; Still, M.; Uytterhoeven, K.
2012ASPC..462..146D Altcode:
We study the internal structure and evolutionary state of KIC 4351319,
a red-giant star observed with the Kepler satellite. The use of
25 individual oscillation frequencies, together with the accurate
atmospheric data provided by ground-based spectroscopic observations,
allowed us to estimate the main parameters of this star with a
level of precision without precedents for a red giant. In addition,
the excellent quality of the observations enabled us to define the
location of the base of the convective envelope and to learn about
the internal rotation, the helium abundance, the surface effects and
extra mixing effects such as diffusion and overshooting.
---------------------------------------------------------
Title: Seismic Evidence for a Rapidly Rotating Core in a
Lower-giant-branch Star Observed with Kepler
Authors: Deheuvels, S.; García, R. A.; Chaplin, W. J.; Basu, S.;
Antia, H. M.; Appourchaux, T.; Benomar, O.; Davies, G. R.; Elsworth,
Y.; Gizon, L.; Goupil, M. J.; Reese, D. R.; Regulo, C.; Schou, J.;
Stahn, T.; Casagrande, L.; Christensen-Dalsgaard, J.; Fischer, D.;
Hekker, S.; Kjeldsen, H.; Mathur, S.; Mosser, B.; Pinsonneault, M.;
Valenti, J.; Christiansen, J. L.; Kinemuchi, K.; Mullally, F.
2012ApJ...756...19D Altcode: 2012arXiv1206.3312D
Rotation is expected to have an important influence on the structure
and the evolution of stars. However, the mechanisms of angular momentum
transport in stars remain theoretically uncertain and very complex to
take into account in stellar models. To achieve a better understanding
of these processes, we desperately need observational constraints on the
internal rotation of stars, which until very recently was restricted to
the Sun. In this paper, we report the detection of mixed modes—i.e.,
modes that behave both as g modes in the core and as p modes in
the envelope—in the spectrum of the early red giant KIC 7341231,
which was observed during one year with the Kepler spacecraft. By
performing an analysis of the oscillation spectrum of the star, we
show that its non-radial modes are clearly split by stellar rotation
and we are able to determine precisely the rotational splittings of
18 modes. We then find a stellar model that reproduces very well the
observed atmospheric and seismic properties of the star. We use this
model to perform inversions of the internal rotation profile of the
star, which enables us to show that the core of the star is rotating at
least five times faster than the envelope. This will shed new light on
the processes of transport of angular momentum in stars. In particular,
this result can be used to place constraints on the angular momentum
coupling between the core and the envelope of early red giants, which
could help us discriminate between the theories that have been proposed
over the last few decades.
---------------------------------------------------------
Title: Estimating the p-mode frequencies of the solar twin 18 Scorpii
Authors: Bazot, M.; Campante, T. L.; Chaplin, W. J.; Carfantan, H.;
Bedding, T. R.; Dumusque, X.; Broomhall, A. -M.; Petit, P.; Théado,
S.; Van Grootel, V.; Arentoft, T.; Castro, M.; Christensen-Dalsgaard,
J.; do Nascimento, J. -D., Jr.; Dintrans, B.; Kjeldsen, H.; Monteiro,
M. J. P. F. G.; Santos, N. C.; Sousa, S.; Vauclair, S.
2012A&A...544A.106B Altcode: 2012arXiv1209.0218B
Solar twins have been a focus of attention for more than a
decade, because their structure is extremely close to that of
the Sun. Today, thanks to high-precision spectrometers, it is
possible to use asteroseismology to probe their interiors. Our
goal is to use time series obtained from the HARPS spectrometer
to extract the oscillation frequencies of 18 Sco, the brightest
solar twin. We used the tools of spectral analysis to estimate these
quantities. We estimate 52 frequencies using an MCMC algorithm. After
examination of their probability densities and comparison with
results from direct MAP optimization, we obtain a minimal set of
21 reliable modes. The identification of each pulsation mode is
straightforwardly accomplished by comparing to the well-established
solar pulsation modes. We also derived some basic seismic indicators
using these values. These results offer a good basis to start
a detailed seismic analysis of 18 Sco using stellar models. <P
/>Based on observations collected at the European Organisation for
Astronomical Research in the Southern Hemisphere, Chile (run ID:
183.D-0729(A)).Results of the MCMC analysis are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/544/A106">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/544/A106</A>
---------------------------------------------------------
Title: Calibrating Convective Properties of Solar-like Stars in the
Kepler Field of View
Authors: Bonaca, Ana; Tanner, Joel D.; Basu, Sarbani; Chaplin,
William J.; Metcalfe, Travis S.; Monteiro, Mário J. P. F. G.; Ballot,
Jérôme; Bedding, Timothy R.; Bonanno, Alfio; Broomhall, Anne-Marie;
Bruntt, Hans; Campante, Tiago L.; Christensen-Dalsgaard, Jørgen;
Corsaro, Enrico; Elsworth, Yvonne; García, Rafael A.; Hekker, Saskia;
Karoff, Christoffer; Kjeldsen, Hans; Mathur, Savita; Régulo, Clara;
Roxburgh, Ian; Stello, Dennis; Trampedach, Regner; Barclay, Thomas;
Burke, Christopher J.; Caldwell, Douglas A.
2012ApJ...755L..12B Altcode: 2012arXiv1207.2765B
Stellar models generally use simple parameterizations to treat
convection. The most widely used parameterization is the so-called
mixing-length theory where the convective eddy sizes are described
using a single number, α, the mixing-length parameter. This is a free
parameter, and the general practice is to calibrate α using the known
properties of the Sun and apply that to all stars. Using data from
NASA's Kepler mission we show that using the solar-calibrated α is not
always appropriate, and that in many cases it would lead to estimates
of initial helium abundances that are lower than the primordial
helium abundance. Kepler data allow us to calibrate α for many other
stars and we show that for the sample of stars we have studied, the
mixing-length parameter is generally lower than the solar value. We
studied the correlation between α and stellar properties, and we find
that α increases with metallicity. We therefore conclude that results
obtained by fitting stellar models or by using population-synthesis
models constructed with solar values of α are likely to have large
systematic errors. Our results also confirm theoretical expectations
that the mixing-length parameter should vary with stellar properties.
---------------------------------------------------------
Title: Planet Occurrence within 0.25 AU of Solar-type Stars from
Kepler
Authors: Howard, Andrew W.; Marcy, Geoffrey W.; Bryson, Stephen T.;
Jenkins, Jon M.; Rowe, Jason F.; Batalha, Natalie M.; Borucki, William
J.; Koch, David G.; Dunham, Edward W.; Gautier, Thomas N., III; Van
Cleve, Jeffrey; Cochran, William D.; Latham, David W.; Lissauer,
Jack J.; Torres, Guillermo; Brown, Timothy M.; Gilliland, Ronald
L.; Buchhave, Lars A.; Caldwell, Douglas A.; Christensen-Dalsgaard,
Jørgen; Ciardi, David; Fressin, Francois; Haas, Michael R.; Howell,
Steve B.; Kjeldsen, Hans; Seager, Sara; Rogers, Leslie; Sasselov,
Dimitar D.; Steffen, Jason H.; Basri, Gibor S.; Charbonneau, David;
Christiansen, Jessie; Clarke, Bruce; Dupree, Andrea; Fabrycky,
Daniel C.; Fischer, Debra A.; Ford, Eric B.; Fortney, Jonathan J.;
Tarter, Jill; Girouard, Forrest R.; Holman, Matthew J.; Johnson,
John Asher; Klaus, Todd C.; Machalek, Pavel; Moorhead, Althea V.;
Morehead, Robert C.; Ragozzine, Darin; Tenenbaum, Peter; Twicken,
Joseph D.; Quinn, Samuel N.; Isaacson, Howard; Shporer, Avi; Lucas,
Philip W.; Walkowicz, Lucianne M.; Welsh, William F.; Boss, Alan;
Devore, Edna; Gould, Alan; Smith, Jeffrey C.; Morris, Robert L.;
Prsa, Andrej; Morton, Timothy D.; Still, Martin; Thompson, Susan E.;
Mullally, Fergal; Endl, Michael; MacQueen, Phillip J.
2012ApJS..201...15H Altcode: 2011arXiv1103.2541H
We report the distribution of planets as a function of planet radius,
orbital period, and stellar effective temperature for orbital periods
less than 50 days around solar-type (GK) stars. These results are based
on the 1235 planets (formally "planet candidates") from the Kepler
mission that include a nearly complete set of detected planets as
small as 2 R <SUB>⊕</SUB>. For each of the 156,000 target stars,
we assess the detectability of planets as a function of planet
radius, R <SUB>p</SUB>, and orbital period, P, using a measure of the
detection efficiency for each star. We also correct for the geometric
probability of transit, R <SUB>sstarf</SUB>/a. We consider first
Kepler target stars within the "solar subset" having T <SUB>eff</SUB>
= 4100-6100 K, log g = 4.0-4.9, and Kepler magnitude Kp < 15 mag,
i.e., bright, main-sequence GK stars. We include only those stars
having photometric noise low enough to permit detection of planets
down to 2 R <SUB>⊕</SUB>. We count planets in small domains of R
<SUB>p</SUB> and P and divide by the included target stars to calculate
planet occurrence in each domain. The resulting occurrence of planets
varies by more than three orders of magnitude in the radius-orbital
period plane and increases substantially down to the smallest radius
(2 R <SUB>⊕</SUB>) and out to the longest orbital period (50 days,
~0.25 AU) in our study. For P < 50 days, the distribution of planet
radii is given by a power law, df/dlog R = k<SUB>R</SUB>R <SUP>α</SUP>
with k<SUB>R</SUB> = 2.9<SUP>+0.5</SUP> <SUB>- 0.4</SUB>, α = -1.92 ±
0.11, and R ≡ R <SUB>p</SUB>/R <SUB>⊕</SUB>. This rapid increase
in planet occurrence with decreasing planet size agrees with the
prediction of core-accretion formation but disagrees with population
synthesis models that predict a desert at super-Earth and Neptune
sizes for close-in orbits. Planets with orbital periods shorter than
2 days are extremely rare; for R <SUB>p</SUB> > 2 R <SUB>⊕</SUB>
we measure an occurrence of less than 0.001 planets per star. For all
planets with orbital periods less than 50 days, we measure occurrence
of 0.130 ± 0.008, 0.023 ± 0.003, and 0.013 ± 0.002 planets per
star for planets with radii 2-4, 4-8, and 8-32 R <SUB>⊕</SUB>,
in agreement with Doppler surveys. We fit occurrence as a function
of P to a power-law model with an exponential cutoff below a critical
period P <SUB>0</SUB>. For smaller planets, P <SUB>0</SUB> has larger
values, suggesting that the "parking distance" for migrating planets
moves outward with decreasing planet size. We also measured planet
occurrence over a broader stellar T <SUB>eff</SUB> range of 3600-7100
K, spanning M0 to F2 dwarfs. Over this range, the occurrence of 2-4 R
<SUB>⊕</SUB> planets in the Kepler field increases with decreasing
T <SUB>eff</SUB>, with these small planets being seven times more
abundant around cool stars (3600-4100 K) than the hottest stars in
our sample (6600-7100 K). <P />Based in part on observations obtained
at the W. M. Keck Observatory, which is operated by the University of
California and the California Institute of Technology.
---------------------------------------------------------
Title: Kepler-36: A Pair of Planets with Neighboring Orbits and
Dissimilar Densities
Authors: Carter, Joshua A.; Agol, Eric; Chaplin, William J.; Basu,
Sarbani; Bedding, Timothy R.; Buchhave, Lars A.; Christensen-Dalsgaard,
Jørgen; Deck, Katherine M.; Elsworth, Yvonne; Fabrycky, Daniel C.;
Ford, Eric B.; Fortney, Jonathan J.; Hale, Steven J.; Handberg,
Rasmus; Hekker, Saskia; Holman, Matthew J.; Huber, Daniel; Karoff,
Christopher; Kawaler, Steven D.; Kjeldsen, Hans; Lissauer, Jack J.;
Lopez, Eric D.; Lund, Mikkel N.; Lundkvist, Mia; Metcalfe, Travis S.;
Miglio, Andrea; Rogers, Leslie A.; Stello, Dennis; Borucki, William J.;
Bryson, Steve; Christiansen, Jessie L.; Cochran, William D.; Geary,
John C.; Gilliland, Ronald L.; Haas, Michael R.; Hall, Jennifer;
Howard, Andrew W.; Jenkins, Jon M.; Klaus, Todd; Koch, David G.;
Latham, David W.; MacQueen, Phillip J.; Sasselov, Dimitar; Steffen,
Jason H.; Twicken, Joseph D.; Winn, Joshua N.
2012Sci...337..556C Altcode: 2012arXiv1206.4718C
In the solar system, the planets’ compositions vary with orbital
distance, with rocky planets in close orbits and lower-density gas
giants in wider orbits. The detection of close-in giant planets around
other stars was the first clue that this pattern is not universal
and that planets’ orbits can change substantially after their
formation. Here, we report another violation of the orbit-composition
pattern: two planets orbiting the same star with orbital distances
differing by only 10% and densities differing by a factor of 8. One
planet is likely a rocky “super-Earth,” whereas the other is more
akin to Neptune. These planets are 20 times more closely spaced and
have a larger density contrast than any adjacent pair of planets in
the solar system.
---------------------------------------------------------
Title: VizieR Online Data Catalog: p-mode frequencies of the solar
twin 18 Sco (Bazot+, 2012)
Authors: Bazot, M.; Campante, T. L.; Chaplin, W. J.; Carfantan, H.;
Bedding, T. R.; Dumusque, X.; Broomhall, A. -M.; Petit, P.; Theado,
S.; Van Grootel, V.; Arentoft, T.; Castro, M.; Christensen-Dalsgaard,
J.; Do Nascimento, J. -D., Jr.; Dintrans, B.; Kjeldsen, H.; Monteiro,
M. J. P. F. G.; Santos, N. C.; Sousa, S.; Vauclair, S.
2012yCat..35440106B Altcode: 2012yCat..35449106B
Results from the estimation of the parameter of the spectrum model using
the Markov Chain Monte-Carlo (MCMC) algorithm described in Sect.4. A
burn-in sequence has been removed. The data is stored in the form of
an array [1975001x54] The first 52 columns give the frequencies of
the modes order by degree (13 l=0 modes, 13 l=1 modes, 13 l=2 modes,
13 l=3 modes). For each mode, they are sorted in ascending order. The
last two columns of each line give the parameters Gamma<SUB>1</SUB>
and Gamma<SUB>2</SUB>. <P />(1 data file).
---------------------------------------------------------
Title: Oscillation mode frequencies of 61 main-sequence and subgiant
stars observed by Kepler
Authors: Appourchaux, T.; Chaplin, W. J.; García, R. A.; Gruberbauer,
M.; Verner, G. A.; Antia, H. M.; Benomar, O.; Campante, T. L.; Davies,
G. R.; Deheuvels, S.; Handberg, R.; Hekker, S.; Howe, R.; Régulo,
C.; Salabert, D.; Bedding, T. R.; White, T. R.; Ballot, J.; Mathur,
S.; Silva Aguirre, V.; Elsworth, Y. P.; Basu, S.; Gilliland, R. L.;
Christensen-Dalsgaard, J.; Kjeldsen, H.; Uddin, K.; Stumpe, M. C.;
Barclay, T.
2012A&A...543A..54A Altcode: 2012arXiv1204.3147A
Context. Solar-like oscillations have been observed by Kepler and CoRoT
in several solar-type stars, thereby providing a way to probe the stars
using asteroseismology <BR /> Aims: We provide the mode frequencies of
the oscillations of various stars required to perform a comparison with
those obtained from stellar modelling. <BR /> Methods: We used a time
series of nine months of data for each star. The 61 stars observed were
categorised in three groups: simple, F-like, and mixed-mode. The simple
group includes stars for which the identification of the mode degree is
obvious. The F-like group includes stars for which the identification
of the degree is ambiguous. The mixed-mode group includes evolved stars
for which the modes do not follow the asymptotic relation of low-degree
frequencies. Following this categorisation, the power spectra of the
61 main-sequence and subgiant stars were analysed using both maximum
likelihood estimators and Bayesian estimators, providing individual mode
characteristics such as frequencies, linewidths, and mode heights. We
developed and describe a methodology for extracting a single set of
mode frequencies from multiple sets derived by different methods and
individual scientists. We report on how one can assess the quality of
the fitted parameters using the likelihood ratio test and the posterior
probabilities. <BR /> Results: We provide the mode frequencies of
61 stars (with their 1-σ error bars), as well as their associated
échelle diagrams. <P />Appendices are available in electronic form
at <A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Accurate fundamental parameters and detailed abundance patterns
from spectroscopy of 93 solar-type Kepler targets
Authors: Bruntt, H.; Basu, S.; Smalley, B.; Chaplin, W. J.; Verner,
G. A.; Bedding, T. R.; Catala, C.; Gazzano, J. -C.; Molenda-Żakowicz,
J.; Thygesen, A. O.; Uytterhoeven, K.; Hekker, S.; Huber, D.; Karoff,
C.; Mathur, S.; Mosser, B.; Appourchaux, T.; Campante, T. L.; Elsworth,
Y.; García, R. A.; Handberg, R.; Metcalfe, T. S.; Quirion, P. -O.;
Régulo, C.; Roxburgh, I. W.; Stello, D.; Christensen-Dalsgaard,
J.; Kawaler, S. D.; Kjeldsen, H.; Morris, R. L.; Quintana, E. V.;
Sanderfer, D. T.
2012MNRAS.423..122B Altcode: 2012arXiv1203.0611B; 2012MNRAS.tmp.3037B
We present a detailed spectroscopic study of 93 solar-type stars
that are targets of the NASA/Kepler mission and provide detailed
chemical composition of each target. We find that the overall
metallicity is well represented by Fe lines. Relative abundances
of light elements (CNO) and α elements are generally higher for
low-metallicity stars. Our spectroscopic analysis benefits from the
accurately measured surface gravity from the asteroseismic analysis
of the Kepler light curves. The accuracy on the log g parameter is
better than 0.03 dex and is held fixed in the analysis. We compare
our T<SUB>eff</SUB> determination with a recent colour calibration of
V<SUB>T</SUB>-K<SUB>S</SUB> [TYCHO V magnitude minus Two Micron All Sky
Survey (2MASS) K<SUB>S</SUB> magnitude] and find very good agreement
and a scatter of only 80 K, showing that for other nearby Kepler
targets, this index can be used. The asteroseismic log g values agree
very well with the classical determination using Fe I-Fe II balance,
although we find a small systematic offset of 0.08 dex (asteroseismic
log g values are lower). The abundance patterns of metals, α elements
and the light elements (CNO) show that a simple scaling by [Fe/H]
is adequate to represent the metallicity of the stars, except for
the stars with metallicity below -0.3, where α-enhancement becomes
important. However, this is only important for a very small fraction of
the Kepler sample. We therefore recommend that a simple scaling with
[Fe/H] be employed in the asteroseismic analyses of large ensembles
of solar-type stars.
---------------------------------------------------------
Title: Solving the Mode Identification Problem in Asteroseismology
of F Stars Observed with Kepler
Authors: White, Timothy R.; Bedding, Timothy R.; Gruberbauer, Michael;
Benomar, Othman; Stello, Dennis; Appourchaux, Thierry; Chaplin,
William J.; Christensen-Dalsgaard, Jørgen; Elsworth, Yvonne P.;
García, Rafael A.; Hekker, Saskia; Huber, Daniel; Kjeldsen, Hans;
Mosser, Benoît; Kinemuchi, Karen; Mullally, Fergal; Still, Martin
2012ApJ...751L..36W Altcode: 2012arXiv1205.0544W
Asteroseismology of F-type stars has been hindered by an ambiguity in
identification of their oscillation modes. The regular mode pattern
that makes this task trivial in cooler stars is masked by increased
line widths. The absolute mode frequencies, encapsulated in the
asteroseismic variable epsilon, can help solve this impasse because
the values of epsilon implied by the two possible mode identifications
are distinct. We find that the correct epsilon can be deduced from the
effective temperature and the line widths and we apply these methods
to a sample of solar-like oscillators observed with Kepler.
---------------------------------------------------------
Title: Seismic evidence for non-synchronization in two close sdb+dM
binaries from Kepler photometry
Authors: Pablo, Herbert; Kawaler, Steven D.; Reed, M. D.; Bloemen, S.;
Charpinet, S.; Hu, H.; Telting, J.; Østensen, R. H.; Baran, A. S.;
Green, E. M.; Hermes, J. J.; Barclay, T.; O'Toole, S. J.; Mullally,
Fergal; Kurtz, D. W.; Christensen-Dalsgaard, J.; Caldwell, Douglas A.;
Christiansen, Jessie L.; Kinemuchi, K.
2012MNRAS.422.1343P Altcode: 2012arXiv1202.3649P
We report on extended photometry of two pulsating subdwarf B (sdB)
stars in close binaries. For both cases, we use rotational splitting of
the pulsation frequencies to show that the sdB component rotates much
too slowly to be in synchronous rotation. We use a theory of tidal
interaction in binary stars to place limits on the mass ratios that
are independent of estimates based on the radial velocity curves. The
companions have masses below 0.26 M<SUB>⊙</SUB>. The pulsation spectra
show the signature of high-overtone g-mode pulsation. One star, KIC
11179657, has a clear sequence of g modes with equal period spacings
as well as several periodicities that depart from that trend. KIC
02991403 shows a similar sequence, but has many more modes that do
not fit the simple pattern.
---------------------------------------------------------
Title: A Uniform Asteroseismic Analysis of 22 Solar-type Stars
Observed by Kepler
Authors: Mathur, S.; Metcalfe, T. S.; Woitaszek, M.; Bruntt, H.;
Verner, G. A.; Christensen-Dalsgaard, J.; Creevey, O. L.; Doǧan, G.;
Basu, S.; Karoff, C.; Stello, D.; Appourchaux, T.; Campante, T. L.;
Chaplin, W. J.; García, R. A.; Bedding, T. R.; Benomar, O.; Bonanno,
A.; Deheuvels, S.; Elsworth, Y.; Gaulme, P.; Guzik, J. A.; Handberg,
R.; Hekker, S.; Herzberg, W.; Monteiro, M. J. P. F. G.; Piau, L.;
Quirion, P. -O.; Régulo, C.; Roth, M.; Salabert, D.; Serenelli, A.;
Thompson, M. J.; Trampedach, R.; White, T. R.; Ballot, J.; Brandão,
I. M.; Molenda-Żakowicz, J.; Kjeldsen, H.; Twicken, J. D.; Uddin,
K.; Wohler, B.
2012ApJ...749..152M Altcode: 2012arXiv1202.2844M
Asteroseismology with the Kepler space telescope is providing not
only an improved characterization of exoplanets and their host stars,
but also a new window on stellar structure and evolution for the
large sample of solar-type stars in the field. We perform a uniform
analysis of 22 of the brightest asteroseismic targets with the highest
signal-to-noise ratio observed for 1 month each during the first year
of the mission, and we quantify the precision and relative accuracy
of asteroseismic determinations of the stellar radius, mass, and age
that are possible using various methods. We present the properties
of each star in the sample derived from an automated analysis of the
individual oscillation frequencies and other observational constraints
using the Asteroseismic Modeling Portal (AMP), and we compare them to
the results of model-grid-based methods that fit the global oscillation
properties. We find that fitting the individual frequencies typically
yields asteroseismic radii and masses to ~1% precision, and ages to
~2.5% precision (respectively, 2, 5, and 8 times better than fitting
the global oscillation properties). The absolute level of agreement
between the results from different approaches is also encouraging,
with model-grid-based methods yielding slightly smaller estimates of
the radius and mass and slightly older values for the stellar age
relative to AMP, which computes a large number of dedicated models
for each star. The sample of targets for which this type of analysis
is possible will grow as longer data sets are obtained during the
remainder of the mission.
---------------------------------------------------------
Title: Commission 12: Solar Radiation and Structure
Authors: Kosovichev, Alexander; Cauzzi, Gianna; Pillet, Valentin
Martinez; Asplund, Martin; Brandenburg, Axel; Chou, Dean-Yi;
Christensen-Dalsgaard, Jorgen; Gan, Weiqun; Kuznetsov, Vladimir D.;
Rovira, Marta G.; Shchukina, Nataliya; Venkatakrishnan, P.
2012IAUTA..28...81K Altcode: 2012IAUTB..28...81K
Commission 12 of the International Astronomical Union encompasses
investigations of the internal structure and dynamics of the Sun, mostly
accessible through the techniques of local and global helioseismology,
the quiet solar atmosphere, solar radiation and its variability, and
the nature of relatively stable magnetic structures like sunspots,
faculae and the magnetic network. The Commission sees participation
of over 350 scientists worldwide.
---------------------------------------------------------
Title: Asteroseismology with Kepler and SONG
Authors: Christensen-Dalsgaard, J.
2012AfrSk..16...74C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Asteroseismology of the Solar Analogs 16 Cyg A and B from
Kepler Observations
Authors: Metcalfe, T. S.; Chaplin, W. J.; Appourchaux, T.; García,
R. A.; Basu, S.; Brandão, I.; Creevey, O. L.; Deheuvels, S.; Doǧan,
G.; Eggenberger, P.; Karoff, C.; Miglio, A.; Stello, D.; Yıldız,
M.; Çelik, Z.; Antia, H. M.; Benomar, O.; Howe, R.; Régulo, C.;
Salabert, D.; Stahn, T.; Bedding, T. R.; Davies, G. R.; Elsworth, Y.;
Gizon, L.; Hekker, S.; Mathur, S.; Mosser, B.; Bryson, S. T.; Still,
M. D.; Christensen-Dalsgaard, J.; Gilliland, R. L.; Kawaler, S. D.;
Kjeldsen, H.; Ibrahim, K. A.; Klaus, T. C.; Li, J.
2012ApJ...748L..10M Altcode: 2012arXiv1201.5966M
The evolved solar-type stars 16 Cyg A and B have long been studied
as solar analogs, yielding a glimpse into the future of our own
Sun. The orbital period of the binary system is too long to provide
meaningful dynamical constraints on the stellar properties, but
asteroseismology can help because the stars are among the brightest
in the Kepler field. We present an analysis of three months of nearly
uninterrupted photometry of 16 Cyg A and B from the Kepler space
telescope. We extract a total of 46 and 41 oscillation frequencies
for the two components, respectively, including a clear detection
of octupole (l = 3) modes in both stars. We derive the properties
of each star independently using the Asteroseismic Modeling Portal,
fitting the individual oscillation frequencies and other observational
constraints simultaneously. We evaluate the systematic uncertainties
from an ensemble of results generated by a variety of stellar evolution
codes and fitting methods. The optimal models derived by fitting each
component individually yield a common age (t = 6.8 ± 0.4 Gyr) and
initial composition (Z <SUB>i</SUB> = 0.024 ± 0.002, Y <SUB>i</SUB> =
0.25 ± 0.01) within the uncertainties, as expected for the components
of a binary system, bolstering our confidence in the reliability of
asteroseismic techniques. The longer data sets that will ultimately
become available will allow future studies of differential rotation,
convection zone depths, and long-term changes due to stellar activity
cycles.
---------------------------------------------------------
Title: Kepler-22b: A 2.4 Earth-radius Planet in the Habitable Zone
of a Sun-like Star
Authors: Borucki, William J.; Koch, David G.; Batalha, Natalie;
Bryson, Stephen T.; Rowe, Jason; Fressin, Francois; Torres,
Guillermo; Caldwell, Douglas A.; Christensen-Dalsgaard, Jørgen;
Cochran, William D.; DeVore, Edna; Gautier, Thomas N.; Geary, John
C.; Gilliland, Ronald; Gould, Alan; Howell, Steve B.; Jenkins,
Jon M.; Latham, David W.; Lissauer, Jack J.; Marcy, Geoffrey W.;
Sasselov, Dimitar; Boss, Alan; Charbonneau, David; Ciardi, David;
Kaltenegger, Lisa; Doyle, Laurance; Dupree, Andrea K.; Ford, Eric B.;
Fortney, Jonathan; Holman, Matthew J.; Steffen, Jason H.; Mullally,
Fergal; Still, Martin; Tarter, Jill; Ballard, Sarah; Buchhave, Lars
A.; Carter, Josh; Christiansen, Jessie L.; Demory, Brice-Olivier;
Désert, Jean-Michel; Dressing, Courtney; Endl, Michael; Fabrycky,
Daniel; Fischer, Debra; Haas, Michael R.; Henze, Christopher; Horch,
Elliott; Howard, Andrew W.; Isaacson, Howard; Kjeldsen, Hans; Johnson,
John Asher; Klaus, Todd; Kolodziejczak, Jeffery; Barclay, Thomas;
Li, Jie; Meibom, Søren; Prsa, Andrej; Quinn, Samuel N.; Quintana,
Elisa V.; Robertson, Paul; Sherry, William; Shporer, Avi; Tenenbaum,
Peter; Thompson, Susan E.; Twicken, Joseph D.; Van Cleve, Jeffrey;
Welsh, William F.; Basu, Sarbani; Chaplin, William; Miglio, Andrea;
Kawaler, Steven D.; Arentoft, Torben; Stello, Dennis; Metcalfe,
Travis S.; Verner, Graham A.; Karoff, Christoffer; Lundkvist, Mia;
Lund, Mikkel N.; Handberg, Rasmus; Elsworth, Yvonne; Hekker, Saskia;
Huber, Daniel; Bedding, Timothy R.; Rapin, William
2012ApJ...745..120B Altcode: 2011arXiv1112.1640B
A search of the time-series photometry from NASA's Kepler spacecraft
reveals a transiting planet candidate orbiting the 11th magnitude G5
dwarf KIC 10593626 with a period of 290 days. The characteristics of the
host star are well constrained by high-resolution spectroscopy combined
with an asteroseismic analysis of the Kepler photometry, leading to
an estimated mass and radius of 0.970 ± 0.060 M <SUB>⊙</SUB> and
0.979 ± 0.020 R <SUB>⊙</SUB>. The depth of 492 ± 10 ppm for the
three observed transits yields a radius of 2.38 ± 0.13 Re for the
planet. The system passes a battery of tests for false positives,
including reconnaissance spectroscopy, high-resolution imaging, and
centroid motion. A full BLENDER analysis provides further validation
of the planet interpretation by showing that contamination of the
target by an eclipsing system would rarely mimic the observed shape
of the transits. The final validation of the planet is provided by
16 radial velocities (RVs) obtained with the High Resolution Echelle
Spectrometer on Keck I over a one-year span. Although the velocities
do not lead to a reliable orbit and mass determination, they are able
to constrain the mass to a 3σ upper limit of 124 M <SUB>⊕</SUB>,
safely in the regime of planetary masses, thus earning the designation
Kepler-22b. The radiative equilibrium temperature is 262 K for a planet
in Kepler-22b's orbit. Although there is no evidence that Kepler-22b
is a rocky planet, it is the first confirmed planet with a measured
radius to orbit in the habitable zone of any star other than the Sun.
---------------------------------------------------------
Title: Masses of Subgiant Stars from Asteroseismology Using the
Coupling Strengths of Mixed Modes
Authors: Benomar, O.; Bedding, T. R.; Stello, D.; Deheuvels, S.;
White, T. R.; Christensen-Dalsgaard, J.
2012ApJ...745L..33B Altcode: 2012arXiv1201.1067B
For a few decades now, asteroseismology, the study of stellar
oscillations, has enabled us to probe the interiors of stars with great
precision. It allows stringent tests of stellar models and can provide
accurate radii, masses, and ages for individual stars. Of particular
interest are the mixed modes that occur in subgiant solar-like stars
since they can place very strong constraints on stellar ages. Here,
we measure the characteristics of the mixed modes, particularly the
coupling strength, using a grid of stellar models for stars with masses
between 0.9 and 1.5 M <SUB>⊙</SUB>. We show that the coupling strength
of the l = 1 mixed modes is predominantly a function of stellar mass
and appears to be independent of metallicity. This should allow an
accurate mass evaluation, further increasing the usefulness of mixed
modes in subgiants as asteroseismic tools.
---------------------------------------------------------
Title: Kepler-21b: A 1.6 R <SUB>Earth</SUB> Planet Transiting the
Bright Oscillating F Subgiant Star HD 179070
Authors: Howell, Steve B.; Rowe, Jason F.; Bryson, Stephen T.; Quinn,
Samuel N.; Marcy, Geoffrey W.; Isaacson, Howard; Ciardi, David R.;
Chaplin, William J.; Metcalfe, Travis S.; Monteiro, Mario J. P. F. G.;
Appourchaux, Thierry; Basu, Sarbani; Creevey, Orlagh L.; Gilliland,
Ronald L.; Quirion, Pierre-Olivier; Stello, Denis; Kjeldsen, Hans;
Christensen-Dalsgaard, Jörgen; Elsworth, Yvonne; García, Rafael
A.; Houdek, Günter; Karoff, Christoffer; Molenda-Żakowicz, Joanna;
Thompson, Michael J.; Verner, Graham A.; Torres, Guillermo; Fressin,
Francois; Crepp, Justin R.; Adams, Elisabeth; Dupree, Andrea; Sasselov,
Dimitar D.; Dressing, Courtney D.; Borucki, William J.; Koch, David
G.; Lissauer, Jack J.; Latham, David W.; Buchhave, Lars A.; Gautier,
Thomas N., III; Everett, Mark; Horch, Elliott; Batalha, Natalie M.;
Dunham, Edward W.; Szkody, Paula; Silva, David R.; Mighell, Ken;
Holberg, Jay; Ballot, Jerôme; Bedding, Timothy R.; Bruntt, Hans;
Campante, Tiago L.; Handberg, Rasmus; Hekker, Saskia; Huber, Daniel;
Mathur, Savita; Mosser, Benoit; Régulo, Clara; White, Timothy R.;
Christiansen, Jessie L.; Middour, Christopher K.; Haas, Michael R.;
Hall, Jennifer R.; Jenkins, Jon M.; McCaulif, Sean; Fanelli, Michael
N.; Kulesa, Craig; McCarthy, Don; Henze, Christopher E.
2012ApJ...746..123H Altcode: 2011arXiv1112.2165H
We present Kepler observations of the bright (V = 8.3), oscillating
star HD 179070. The observations show transit-like events which
reveal that the star is orbited every 2.8 days by a small, 1.6 R
<SUB>Earth</SUB> object. Seismic studies of HD 179070 using short
cadence Kepler observations show that HD 179070 has a frequency-power
spectrum consistent with solar-like oscillations that are acoustic
p-modes. Asteroseismic analysis provides robust values for the mass
and radius of HD 179070, 1.34 ± 0.06 M <SUB>⊙</SUB> and 1.86 ±
0.04 R <SUB>⊙</SUB>, respectively, as well as yielding an age of
2.84 ± 0.34 Gyr for this F5 subgiant. Together with ground-based
follow-up observations, analysis of the Kepler light curves and
image data, and blend scenario models, we conservatively show at the
>99.7% confidence level (3σ) that the transit event is caused by
a 1.64 ± 0.04 R <SUB>Earth</SUB> exoplanet in a 2.785755 ± 0.000032
day orbit. The exoplanet is only 0.04 AU away from the star and our
spectroscopic observations provide an upper limit to its mass of ~10 M
<SUB>Earth</SUB> (2σ). HD 179070 is the brightest exoplanet host star
yet discovered by Kepler. <P />Based in part on observations obtained
at the W. M. Keck Observatory, which is operated by the University
of California and the California Institute of Technology, the Mayall
telescope at Kitt Peak National Observatory, and the WIYN Observatory
which is a joint facility of NOAO, University of Wisconsin-Madison,
Indiana University, and Yale University.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Kepler compact pulsator candidates
(Ostensen+, 2011)
Authors: Ostensen, R. H.; Silvotti, R.; Charpinet, S.; Oreiro, R.;
Bloemen, S.; Baran, A. S.; Reed, M. D.; Kawaler, S. D.; Telting,
J. H.; Green, E. M.; O'Toole, S. J.; Aerts, C.; Gansicke, B. T.;
Marsh, T. R.; Breedt, E.; Heber, U.; Koester, D.; Quint, A. C.; Kurtz,
D. W.; Rodriguez-Lopez, C.; Vuckovic, M.; Ottosen, T. A.; Frimann, S.;
Somero, A.; Wilson, P. A.; Thygesen, A. O.; Lindberg, J. E.; Kjeldsen,
H.; Christensen-Dalsgaard, J.; Allen, C.; McCauliff, S.; Middour, C. K.
2012yCat..74142860O Altcode:
We present results from the final 6 months of a survey to search for
pulsations in white dwarfs (WDs) and hot subdwarf stars with the Kepler
spacecraft. Spectroscopic observations are used to separate the objects
into accurate classes, and we explore the physical parameters of the
subdwarf B (sdB) stars and white dwarfs in the sample. From the Kepler
photometry and our spectroscopic data, we find that the sample contains
five new pulsators of the V1093 Her type, one AM CVn type cataclysmic
variable and a number of other binary systems. <P />(1 data file).
---------------------------------------------------------
Title: Fundamental properties of five Kepler stars using global
asteroseismic quantities and ground-based observations
Authors: Creevey, O. L.; Doǧan, G.; Frasca, A.; Thygesen, A. O.;
Basu, S.; Bhattacharya, J.; Biazzo, K.; Brandão, I. M.; Bruntt, H.;
Mazumdar, A.; Niemczura, E.; Shrotriya, T.; Sousa, S. G.; Stello, D.;
Subramaniam, A.; Campante, T. L.; Handberg, R.; Mathur, S.; Bedding,
T. R.; García, R. A.; Régulo, C.; Salabert, D.; Molenda-Żakowicz,
J.; Quirion, P. -O.; White, T. R.; Bonanno, A.; Chaplin, W. J.;
Christensen-Dalsgaard, J.; Christiansen, J. L.; Elsworth, Y.; Fanelli,
M. N.; Karoff, C.; Kinemuchi, K.; Kjeldsen, H.; Gai, N.; Monteiro,
M. J. P. F. G.; Suárez, J. C.
2012A&A...537A.111C Altcode: 2011arXiv1111.4615C
We present an asteroseismic study of the solar-like stars KIC 11395018,
KIC 10273246, KIC 10920273, KIC 10339342, and KIC 11234888 using
short-cadence time series of more than eight months from the Kepler
satellite. For four of these stars, we derive atmospheric parameters
from spectra acquired with the Nordic Optical Telescope. The global
seismic quantities (average largefrequency separation and frequency
of maximum power), combined with the atmospheric parameters, yield
the mean density and surface gravity with precisions of 2% and ~0.03
dex, respectively. We also determine the radius, mass, and age with
precisions of 2-5%, 7-11%, and ~35%, respectively, using grid-based
analyses. Coupling the stellar parameters with photometric data yields
an asteroseismic distance with a precision better than 10%. A vsini
measurement provides a rotational period-inclination correlation, and
using the rotational periods from the recent literature, we constrain
the stellar inclination for three of the stars. An Li abundance analysis
yields an independent estimate of the age, but this is inconsistent
with the asteroseismically determined age for one of the stars. We
assess the performance of five grid-based analysis methods and find
them all to provide consistent values of the surface gravity to ~0.03
dex when both atmospheric and seismic constraints are at hand. The
different grid-based analyses all yield fitted values of radius and
mass to within 2.4σ, and taking the mean of these results reduces
it to 1.5σ. The absence of a metallicity constraint when the average
large frequency separation is measured with a precision of 1% biases
the fitted radius and mass for the stars with non-solar metallicity
(metal-rich KIC 11395018 and metal-poor KIC 10273246), while including
a metallicity constraint reduces the uncertainties in both of these
parameters by almost a factor of two. We found that including the
average small frequency separation improves the determination of the
age only for KIC 11395018 and KIC 11234888, and for the latter this
improvement was due to the lack of strong atmospheric constraints.
---------------------------------------------------------
Title: Fast core rotation in red-giant stars as revealed by
gravity-dominated mixed modes
Authors: Beck, Paul G.; Montalban, Josefina; Kallinger, Thomas;
De Ridder, Joris; Aerts, Conny; García, Rafael A.; Hekker, Saskia;
Dupret, Marc-Antoine; Mosser, Benoit; Eggenberger, Patrick; Stello,
Dennis; Elsworth, Yvonne; Frandsen, Søren; Carrier, Fabien; Hillen,
Michel; Gruberbauer, Michael; Christensen-Dalsgaard, Jørgen; Miglio,
Andrea; Valentini, Marica; Bedding, Timothy R.; Kjeldsen, Hans;
Girouard, Forrest R.; Hall, Jennifer R.; Ibrahim, Khadeejah A.
2012Natur.481...55B Altcode: 2011arXiv1112.2825B
When the core hydrogen is exhausted during stellar evolution, the
central region of a star contracts and the outer envelope expands
and cools, giving rise to a red giant. Convection takes place over
much of the star's radius. Conservation of angular momentum requires
that the cores of these stars rotate faster than their envelopes;
indirect evidence supports this. Information about the angular-momentum
distribution is inaccessible to direct observations, but it can be
extracted from the effect of rotation on oscillation modes that probe
the stellar interior. Here we report an increasing rotation rate from
the surface of the star to the stellar core in the interiors of red
giants, obtained using the rotational frequency splitting of recently
detected `mixed modes'. By comparison with theoretical stellar models,
we conclude that the core must rotate at least ten times faster
than the surface. This observational result confirms the theoretical
prediction of a steep gradient in the rotation profile towards the
deep stellar interior.
---------------------------------------------------------
Title: Nitty-gritty Modeling Details - Geeking Out on Precision
Frequencies for Comparison Sake
Authors: Christensen-Dalsgaard, Jörgen; Hu, Haili
2011asa..progE..23C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Calculating Asteroseismic Diagrams for Solar-like Oscillations
Authors: White, Timothy R.; Bedding, Timothy R.; Stello, Dennis;
Christensen-Dalsgaard, Jørgen; Huber, Daniel; Kjeldsen, Hans
2011ApJ...743..161W Altcode: 2011arXiv1109.3455W
With the success of the Kepler and CoRoT missions, the number of
stars with detected solar-like oscillations has increased by several
orders of magnitude; for the first time we are able to perform
large-scale ensemble asteroseismology of these stars. In preparation
for this golden age of asteroseismology we have computed expected
values of various asteroseismic observables from models of varying
mass and metallicity. The relationships between these asteroseismic
observables, such as the separations between mode frequencies, are able
to significantly constrain estimates of the ages and masses of these
stars. We investigate the scaling relation between the large frequency
separation, Δν, and mean stellar density. Furthermore we present
model evolutionary tracks for several asteroseismic diagrams. We
have extended the so-called C-D diagram beyond the main sequence
to the subgiants and the red giant branch. We also consider another
asteroseismic diagram, the epsilon diagram, which is more sensitive to
variations in stellar properties at the subgiant stages and can aid
in determining the correct mode identification. The recent discovery
of gravity-mode period spacings in red giants forms the basis for a
third asteroseismic diagram. We compare the evolutionary model tracks
in these asteroseismic diagrams with results from pre-Kepler studies
of solar-like oscillations and early results from Kepler.
---------------------------------------------------------
Title: Testing Scaling Relations for Solar-like Oscillations from
the Main Sequence to Red Giants Using Kepler Data
Authors: Huber, D.; Bedding, T. R.; Stello, D.; Hekker, S.; Mathur,
S.; Mosser, B.; Verner, G. A.; Bonanno, A.; Buzasi, D. L.; Campante,
T. L.; Elsworth, Y. P.; Hale, S. J.; Kallinger, T.; Silva Aguirre,
V.; Chaplin, W. J.; De Ridder, J.; García, R. A.; Appourchaux,
T.; Frandsen, S.; Houdek, G.; Molenda-Żakowicz, J.; Monteiro,
M. J. P. F. G.; Christensen-Dalsgaard, J.; Gilliland, R. L.; Kawaler,
S. D.; Kjeldsen, H.; Broomhall, A. M.; Corsaro, E.; Salabert, D.;
Sanderfer, D. T.; Seader, S. E.; Smith, J. C.
2011ApJ...743..143H Altcode: 2011arXiv1109.3460H
We have analyzed solar-like oscillations in ~1700 stars observed by the
Kepler Mission, spanning from the main sequence to the red clump. Using
evolutionary models, we test asteroseismic scaling relations for the
frequency of maximum power (ν<SUB>max</SUB>), the large frequency
separation (Δν), and oscillation amplitudes. We show that the
difference of the Δν-ν<SUB>max</SUB> relation for unevolved and
evolved stars can be explained by different distributions in effective
temperature and stellar mass, in agreement with what is expected from
scaling relations. For oscillation amplitudes, we show that neither
(L/M)<SUP> s </SUP> scaling nor the revised scaling relation by Kjeldsen
& Bedding is accurate for red-giant stars, and demonstrate that a
revised scaling relation with a separate luminosity-mass dependence can
be used to calculate amplitudes from the main sequence to red giants
to a precision of ~25%. The residuals show an offset particularly for
unevolved stars, suggesting that an additional physical dependency is
necessary to fully reproduce the observed amplitudes. We investigate
correlations between amplitudes and stellar activity, and find evidence
that the effect of amplitude suppression is most pronounced for subgiant
stars. Finally, we test the location of the cool edge of the instability
strip in the Hertzsprung-Russell diagram using solar-like oscillations
and find the detections in the hottest stars compatible with a domain
of hybrid stochastically excited and opacity driven pulsation.
---------------------------------------------------------
Title: Modeling Kepler Observations of Solar-like Oscillations in
the Red Giant Star HD 186355
Authors: Jiang, C.; Jiang, B. W.; Christensen-Dalsgaard, J.; Bedding,
T. R.; Stello, D.; Huber, D.; Frandsen, S.; Kjeldsen, H.; Karoff, C.;
Mosser, B.; Demarque, P.; Fanelli, M. N.; Kinemuchi, K.; Mullally, F.
2011ApJ...742..120J Altcode: 2011arXiv1109.0962J
We have analyzed oscillations of the red giant star HD 186355
observed by the NASA Kepler satellite. The data consist of the first
five quarters of science operations of Kepler, which cover about 13
months. The high-precision time-series data allow us to accurately
extract the oscillation frequencies from the power spectrum. We find
that the frequency of the maximum oscillation power, ν<SUB>max</SUB>,
and the mean large frequency separation, Δν, are around 106 and
9.4 μHz, respectively. A regular pattern of radial and non-radial
oscillation modes is identified by stacking the power spectra
in an echelle diagram. We use the scaling relations of Δν and
ν<SUB>max</SUB> to estimate the preliminary asteroseismic mass,
which is confirmed with the modeling result (M = 1.45 ± 0.05 M
<SUB>⊙</SUB>) using the Yale Rotating stellar Evolution Code
(YREC7). In addition, we constrain the effective temperature,
luminosity, and radius from comparisons between observational
constraints and models. A number of mixed l = 1 modes are also
detected and taken into account in our model comparisons. We find
a mean observational period spacing for these mixed modes of about
58 s, suggesting that this red giant branch star is in the shell
hydrogen-burning phase.
---------------------------------------------------------
Title: Spin-Orbit Alignment for the Circumbinary Planet Host
Kepler-16 A
Authors: Winn, Joshua N.; Albrecht, Simon; Johnson, John Asher; Torres,
Guillermo; Cochran, William D.; Marcy, Geoffrey W.; Howard, Andrew W.;
Isaacson, Howard; Fischer, Debra; Doyle, Laurance; Welsh, William;
Carter, Joshua A.; Fabrycky, Daniel C.; Ragozzine, Darin; Quinn,
Samuel N.; Shporer, Avi; Howell, Steve B.; Latham, David W.; Orosz,
Jerome; Prsa, Andrej; Slawson, Robert W.; Borucki, William J.; Koch,
David; Barclay, Thomas; Boss, Alan P.; Christensen-Dalsgaard, Jørgen;
Girouard, Forrest R.; Jenkins, Jon; Klaus, Todd C.; Meibom, Søren;
Morris, Robert L.; Sasselov, Dimitar; Still, Martin; Van Cleve, Jeffrey
2011ApJ...741L...1W Altcode: 2011arXiv1109.3198W
Kepler-16 is an eccentric low-mass eclipsing binary with a
circumbinary transiting planet. Here, we investigate the angular
momentum of the primary star, based on Kepler photometry and Keck
spectroscopy. The primary star's rotation period is 35.1 ± 1.0 days,
and its projected obliquity with respect to the stellar binary orbit
is 1fdg6 ± 2fdg4. Therefore, the three largest sources of angular
momentum—the stellar orbit, the planetary orbit, and the primary's
rotation—are all closely aligned. This finding supports a formation
scenario involving accretion from a single disk. Alternatively, tides
may have realigned the stars despite their relatively wide separation
(0.2 AU), a hypothesis that is supported by the agreement between the
measured rotation period and the "pseudosynchronous" period of tidal
evolution theory. The rotation period, chromospheric activity level,
and fractional light variations suggest a main-sequence age of 2-4
Gyr. Evolutionary models of low-mass stars can match the observed
masses and radii of the primary and secondary stars to within about 3%.
---------------------------------------------------------
Title: The SONG project and the prototype node at Tenerife
Authors: Uytterhoeven, K.; Palle, P. L.; Grundahl, F.; Frandsen, S.;
Kjeldsen, H.; Christensen-Dalsgaard, J.; Fredslund Andersen, M.;
Weiss, E.; Joergensen, U. G.; Rasmussen, P. K.; Soerensen, A. N.;
Harpsoee, K.; Skottfelt, J.
2011arXiv1111.1834U Altcode:
SONG (Stellar Observations Network Group) is a global network of 1-m
class robotic telescopes that is under development. The SONG prototype
will shortly be operational at Observatorio del Teide, Tenerife, and
first light is expected by December 2011. The main scientific goals of
the SONG project are asteroseismology of bright stars and follow-up
and characterization of exo-planets by means of precise measurements
of stellar surface motions and brightness variations. We present the
Tenerife SONG node and its instruments.
---------------------------------------------------------
Title: VizieR Online Data Catalog: BVRI light curves of KIC Cepheids
(Szabo+, 2011)
Authors: Szabo, R.; Szabados, L.; Ngeow, C. -C.; Smolec, R.;
Derekas, A.; Moskalik, P.; Nuspl, J.; Lehmann, H.; Furesz, G.;
Molenda-Zakowicz, J.; Bryson, S. T.; Henden, A. A.; Kurtz, D. W.;
Stello, D.; Nemec, J. M.; Benko, J. M.; Berdnikov, L.; Bruntt, H.;
Evans, N. R.; Gorynya, N. A.; Pastukhova, E. N.; Simcoe, R. J.;
Grindlay, J. E.; Los, E. J.; Doane, A.; Laycock, S. G.; Mink, D. J.;
Champine, G.; Sliski, A.; Handler, G.; Kiss, L. L.; Kollath, Z.;
Kovacs, J.; Christensen-Dalsgaard, J.; Kjeldsen, H.; Allen, C.;
Thompson, S. E.; van Cleve, J.
2011yCat..74132709S Altcode:
We report results of initial work done on selected candidate Cepheids
to be observed with the Kepler space telescope. Prior to the launch,
40 candidates were selected from previous surveys and data bases. The
analysis of the first 322d of Kepler photometry, and recent ground-based
follow-up multicolour photometry and spectroscopy allowed us to confirm
that one of these stars, V1154 Cyg (KIC 7548061), is indeed a 4.9d
Cepheid. Using the phase lag method, we show that this star pulsates
in the fundamental mode. New radial velocity data are consistent with
previous measurements, suggesting that a long-period binary component is
unlikely. No evidence is seen in the ultraprecise, nearly uninterrupted
Kepler photometry for non-radial or stochastically excited modes at
the micromagnitude level. The other candidates are not Cepheids, but
an interesting mix of possible spotted stars, eclipsing systems and
flare stars. <P />(5 data files).
---------------------------------------------------------
Title: VizieR Online Data Catalog: Kepler planetary
candidates. I. (Borucki+, 2011)
Authors: Borucki, W. J.; Koch, D. G.; Basri, G.; Batalha, N.; Boss,
A.; Brown, T. M.; Caldwell, D.; Christensen-Dalsgaard, J.; Cochran,
W. D.; DeVore, E.; Dunham, E. W.; Dupree, A. K.; Gautier, T. N.,
III; Geary, J. C.; Gilliland, R.; Gould, A.; Howell, S. B.; Jenkins,
J. M.; Kjeldsen, H.; Latham, D. W.; Lissauer, J. J.; Marcy, G. W.;
Monet, D. G.; Sasselov, D.; Tarter, J.; Charbonneau, D.; Doyle, L.;
Ford, E. B.; Fortney, J.; Holman, M. J.; Seager, S.; Steffen, J. H.;
Welsh, W. F.; Allen, C.; Bryson, S. T.; Buchhave, L.; Chandrasekaran,
H.; Christiansen, J. L.; Ciardi, D.; Clarke, B. D.; Dotson, J. L.;
Endl, M.; Fischer, D.; Fressin, F.; Haas, M.; Horch, E.; Howard,
A.; Isaacson, H.; Kolodziejczak, J.; Li, J.; MacQueen, P.; Meibom,
S.; Prsa, A.; Quintana, E. V.; Rowe, J.; Sherry, W.; Tenenbaum, P.;
Torres, G.; Twicken, J. D.; van Cleve, J.; Walkowicz, L.; Wu, H.
2011yCat..17280117B Altcode:
In the spring of 2009, the Kepler Mission commenced high-precision
photometry on nearly 156000 stars to determine the frequency and
characteristics of small exoplanets, conduct a guest observer program,
and obtain asteroseismic data on a wide variety of stars. On 2010
June 15, the Kepler Mission released most of the data from the first
quarter of observations. At the time of this data release, 705 stars
from this first data set have exoplanet candidates with sizes from as
small as that of Earth to larger than that of Jupiter. Here we give
the identity and characteristics of 305 released stars with planetary
candidates. Data for the remaining 400 stars with planetary candidates
will be released in 2011 February. More than half the candidates on
the released list have radii less than half that of Jupiter. Five
candidates are present in and near the habitable zone; two near
super-Earth size, and three bracketing the size of Jupiter. The
released stars also include five possible multi-planet systems. One
of these has two Neptune-size (2.3 and 2.5 Earth radius) candidates
with near-resonant periods. <P />(1 data file).
---------------------------------------------------------
Title: VizieR Online Data Catalog: Kepler planetary
candidates. II. (Borucki+, 2011)
Authors: Borucki, W. J.; Koch, D. G.; Basri, G.; Batalha, N.; Brown,
T. M.; Bryson, S. T.; Caldwell, D.; Christensen-Dalsgaard, J.;
Cochran, W. D.; DeVore, E.; Dunham, E. W.; Gautier, T. N.; Geary,
J. C.; Gilliland, R.; Gould, A.; Howell, S. B.; Jenkins, J. M.;
Latham, D. W.; Lissauer, J. J.; Marcy, G. W.; Rowe, J.; Sasselov,
D.; Boss, A.; Charbonneau, D.; Ciardi, D.; Doyle, L.; Dupree, A. K.;
Ford, E. B.; Fortney, J.; Holman, M. J.; Seager, S.; Steffen, J. H.;
Tarter, J.; Welsh, W. F.; Allen, C.; Buchhave, L. A.; Christiansen,
J. L.; Clarke, B. D.; Das, S.; Desert, J. -M.; Endl, M.; Fabrycky,
D.; Fressin, F.; Haas, M.; Horch, E.; Howard, A.; Isaacson, H.;
Kjeldsen, H.; Kolodziejczak, J.; Kulesa, C.; Li, J.; Lucas, P. W.;
Machalek, P.; McCarthy, D.; MacQueen, P.; Meibom, S.; Miquel, T.;
Prsa, A.; Quinn, S. N.; Quintana, E. V.; Ragozzine, D.; Sherry, W.;
Shporer, A.; Tenenbaum, P.; Torres, G.; Twicken, J. D.; van Cleve,
J.; Walkowicz, L.; Witteborn, F. C.; Still, M.
2011yCat..17360019B Altcode:
The results discussed in this paper are based on three data segments:
the first segment (labeled Q0) started on JD 2454953.53 and ended on
2454963.25 and was taken during commissioning operations, the second
data segment (labeled Q1) taken at the beginning of science operations
that started on JD 2454964.50 and finished on JD 2454997.99, and a
third segment (labeled Q2) starting on JD 2455002.51 and finishing on
JD 2455091.48. The durations of the segments are 9.7, 33.5, and 89.0
days, respectively. The observations span a total period of 137.95
days including the gaps. A total of 156097 long cadence (LC) targets
in Q1, and 166247 LC and 1492 short cadence (SC) targets in Q2 were
observed. The results reported here are for the LC observations of
153196 stars observed during Q2. The selected stars are primarily
main-sequence dwarfs chosen from the Kepler Input Catalog (KIC,
Cat. V/133). <P />(4 data files).
---------------------------------------------------------
Title: Asteroseismic Diagrams from a Survey of Solar-like Oscillations
with Kepler
Authors: White, Timothy R.; Bedding, Timothy R.; Stello, Dennis;
Appourchaux, Thierry; Ballot, Jérôme; Benomar, Othman; Bonanno,
Alfio; Broomhall, Anne-Marie; Campante, Tiago L.; Chaplin, William
J.; Christensen-Dalsgaard, Jørgen; Corsaro, Enrico; Doǧan, Gülnur;
Elsworth, Yvonne P.; Fletcher, Stephen T.; García, Rafael A.; Gaulme,
Patrick; Handberg, Rasmus; Hekker, Saskia; Huber, Daniel; Karoff,
Christoffer; Kjeldsen, Hans; Mathur, Savita; Mosser, Benoit; Monteiro,
Mario J. P. F. G.; Régulo, Clara; Salabert, David; Silva Aguirre,
Victor; Thompson, Michael J.; Verner, Graham; Morris, Robert L.;
Sanderfer, Dwight T.; Seader, Shawn E.
2011ApJ...742L...3W Altcode: 2011arXiv1110.1375W
Photometric observations made by the NASA Kepler Mission have led to a
dramatic increase in the number of main-sequence and subgiant stars with
detected solar-like oscillations. We present an ensemble asteroseismic
analysis of 76 solar-type stars. Using frequencies determined from the
Kepler time-series photometry, we have measured three asteroseismic
parameters that characterize the oscillations: the large frequency
separation (Δν), the small frequency separation between modes of
l = 0 and l = 2 (δν<SUB>02</SUB>), and the dimensionless offset
(epsilon). These measurements allow us to construct asteroseismic
diagrams, namely the so-called Christensen-Dalsgaard diagram of
δν<SUB>02</SUB> versus Δν, and the recently re-introduced epsilon
diagram. We compare the Kepler results with previously observed
solar-type stars and with theoretical models. The positions of
stars in these diagrams places constraints on their masses and
ages. Additionally, we confirm the observational relationship
between epsilon and T <SUB>eff</SUB> that allows for the unambiguous
determination of radial order and should help resolve the problem of
mode identification in F stars.
---------------------------------------------------------
Title: The Observatorio del Teide welcomes SONG:the Stellar
Observations Network Group
Authors: Creevey, O. L.; Grundahl, F.; Pallé, P. L.; Gråe Jørgensen,
U.; Belmonte, J. A.; Christensen-Dalsgaard, J.; Frandsen, S.; Kjeldsen,
H.; Kjærgaard, P.
2011hsa6.conf..686C Altcode: 2011arXiv1112.5539C
The Stellar Observations Network Group (SONG) is an internationalnetwork
project aiming to place eight 1 m robotic telescopes around the
globe,with the primary objectives of studying stellar oscillations
and planetsusing ultra-precision radial velocity measurements.The
prototype of SONG will be installed and running at the Observatoriodel
Teide by Summer 2011. In these proceedings we present the project,
primary scientific objectives, and instrument, and discussthe observing
possibilities for the Spanish community.
---------------------------------------------------------
Title: Constructing a One-solar-mass Evolutionary Sequence Using
Asteroseismic Data from Kepler
Authors: Silva Aguirre, V.; Chaplin, W. J.; Ballot, J.; Basu,
S.; Bedding, T. R.; Serenelli, A. M.; Verner, G. A.; Miglio, A.;
Monteiro, M. J. P. F. G.; Weiss, A.; Appourchaux, T.; Bonanno,
A.; Broomhall, A. M.; Bruntt, H.; Campante, T. L.; Casagrande, L.;
Corsaro, E.; Elsworth, Y.; García, R. A.; Gaulme, P.; Handberg,
R.; Hekker, S.; Huber, D.; Karoff, C.; Mathur, S.; Mosser, B.;
Salabert, D.; Schönrich, R.; Sousa, S. G.; Stello, D.; White, T. R.;
Christensen-Dalsgaard, J.; Gilliland, R. L.; Kawaler, S. D.; Kjeldsen,
H.; Houdek, G.; Metcalfe, T. S.; Molenda-Żakowicz, J.; Thompson,
M. J.; Caldwell, D. A.; Christiansen, J. L.; Wohler, B.
2011ApJ...740L...2S Altcode: 2011arXiv1108.2031S
Asteroseismology of solar-type stars has entered a new era of
large surveys with the success of the NASA Kepler mission, which
is providing exquisite data on oscillations of stars across the
Hertzsprung-Russell diagram. From the time-series photometry, the two
seismic parameters that can be most readily extracted are the large
frequency separation (Δν) and the frequency of maximum oscillation
power (ν<SUB>max</SUB>). After the survey phase, these quantities
are available for hundreds of solar-type stars. By scaling from solar
values, we use these two asteroseismic observables to identify for the
first time an evolutionary sequence of 1 M <SUB>sun</SUB> field stars,
without the need for further information from stellar models. Comparison
of our determinations with the few available spectroscopic results
shows an excellent level of agreement. We discuss the potential of the
method for differential analysis throughout the main-sequence evolution
and the possibility of detecting twins of very well-known stars.
---------------------------------------------------------
Title: The Kepler characterization of the variability among A-
and F-type stars. I. General overview
Authors: Uytterhoeven, K.; Moya, A.; Grigahcène, A.; Guzik,
J. A.; Gutiérrez-Soto, J.; Smalley, B.; Handler, G.; Balona,
L. A.; Niemczura, E.; Fox Machado, L.; Benatti, S.; Chapellier, E.;
Tkachenko, A.; Szabó, R.; Suárez, J. C.; Ripepi, V.; Pascual, J.;
Mathias, P.; Martín-Ruíz, S.; Lehmann, H.; Jackiewicz, J.; Hekker,
S.; Gruberbauer, M.; García, R. A.; Dumusque, X.; Díaz-Fraile, D.;
Bradley, P.; Antoci, V.; Roth, M.; Leroy, B.; Murphy, S. J.; De Cat,
P.; Cuypers, J.; Kjeldsen, H.; Christensen-Dalsgaard, J.; Breger, M.;
Pigulski, A.; Kiss, L. L.; Still, M.; Thompson, S. E.; van Cleve, J.
2011A&A...534A.125U Altcode: 2011arXiv1107.0335U
Context. The Kepler spacecraft is providing time series of photometric
data with micromagnitude precision for hundreds of A-F type stars. <BR
/> Aims: We present a first general characterization of the pulsational
behaviour of A-F type stars as observed in the Kepler light curves
of a sample of 750 candidate A-F type stars, and observationally
investigate the relation between γ Doradus (γ Dor), δ Scuti
(δ Sct), and hybrid stars. <BR /> Methods: We compile a database
of physical parameters for the sample stars from the literature and
new ground-based observations. We analyse the Kepler light curve of
each star and extract the pulsational frequencies using different
frequency analysis methods. We construct two new observables, "energy"
and "efficiency", related to the driving energy of the pulsation
mode and the convective efficiency of the outer convective zone,
respectively. <BR /> Results: We propose three main groups to describe
the observed variety in pulsating A-F type stars: γ Dor, δ Sct, and
hybrid stars. We assign 63% of our sample to one of the three groups,
and identify the remaining part as rotationally modulated/active stars,
binaries, stars of different spectral type, or stars that show no clear
periodic variability. 23% of the stars (171 stars) are hybrid stars,
which is a much higher fraction than what has been observed before. We
characterize for the first time a large number of A-F type stars (475
stars) in terms of number of detected frequencies, frequency range,
and typical pulsation amplitudes. The majority of hybrid stars show
frequencies with all kinds of periodicities within the γ Dor and δ
Sct range, also between 5 and 10 d<SUP>-1</SUP>, which is a challenge
for the current models. We find indications for the existence of δ
Sct and γ Dor stars beyond the edges of the current observational
instability strips. The hybrid stars occupy the entire region within
the δ Sct and γ Dor instability strips and beyond. Non-variable
stars seem to exist within the instability strips. The location of
γ Dor and δ Sct classes in the (T<SUB>eff</SUB>, log g)-diagram
has been extended. We investigate two newly constructed variables,
"efficiency" and "energy", as a means to explore the relation between
γ Dor and δ Sct stars. <BR /> Conclusions: Our results suggest a
revision of the current observational instability strips of δ Sct and
γ Dor stars and imply an investigation of pulsation mechanisms to
supplement the κ mechanism and convective blocking effect to drive
hybrid pulsations. Accurate physical parameters for all stars are
needed to confirm these findings.
---------------------------------------------------------
Title: Fourier analysis of non-Blazhko ab-type RR Lyrae stars observed
with the Kepler space telescope
Authors: Nemec, J. M.; Smolec, R.; Benkő, J. M.; Moskalik, P.;
Kolenberg, K.; Szabó, R.; Kurtz, D. W.; Bryson, S.; Guggenberger,
E.; Chadid, M.; Jeon, Y. -B.; Kunder, A.; Layden, A. C.; Kinemuchi,
K.; Kiss, L. L.; Poretti, E.; Christensen-Dalsgaard, J.; Kjeldsen,
H.; Caldwell, D.; Ripepi, V.; Derekas, A.; Nuspl, J.; Mullally, F.;
Thompson, S. E.; Borucki, W. J.
2011MNRAS.417.1022N Altcode: 2011arXiv1106.6120N; 2011MNRAS.tmp.1514N
Nineteen of the ∼40 RR Lyr stars in the Kepler field have been
identified as candidate non-Blazhko (or unmodulated) stars. In
this paper we present the results of Fourier decomposition of the
time-series photometry of these stars acquired during the first 417
d of operation (Q0-Q5) of the Kepler telescope. Fourier parameters
based on ∼18 400 long-cadence observations per star (and ∼150 000
short-cadence observations for FN Lyr and for AW Dra) are derived. None
of the stars shows the recently discovered 'period-doubling' effect
seen in Blazhko variables; however, KIC 7021124 has been found to
pulsate simultaneously in the fundamental and second overtone modes
with a period ratio P<SUB>2</SUB>/P<SUB>0</SUB>∼ 0.593 05 and is
similar to the double-mode star V350 Lyr. Period change rates are
derived from O - C diagrams spanning, in some cases, over 100 years;
these are compared with high-precision periods derived from the
Kepler data alone. Extant Fourier correlations by Kovács, Jurcsik et
al. (with minor transformations from the V to the Kp passband) have
been used to derive underlying physical characteristics for all the
stars. This procedure seems to be validated through comparisons of
the Kepler variables with Galactic and Large Magellanic Cloud (LMC)
RR Lyr stars. The most metal-poor star in the sample is NR Lyr, with
[Fe/H] =-2.3 dex; and the four most metal-rich stars have [Fe/H]
ranging from -0.6 to +0.1 dex. Pulsational luminosities and masses
are found to be systematically smaller than L and ? values derived
from stellar evolution models, and are favoured over the evolutionary
values when periods are computed with the Warsaw linear hydrodynamics
code. Finally, the Fourier parameters are compared with theoretical
values derived using the Warsaw non-linear convective pulsation code.
---------------------------------------------------------
Title: Asteroseismology from multi-month Kepler photometry: the
evolved Sun-like stars KIC 10273246 and KIC 10920273
Authors: Campante, T. L.; Handberg, R.; Mathur, S.; Appourchaux, T.;
Bedding, T. R.; Chaplin, W. J.; García, R. A.; Mosser, B.; Benomar,
O.; Bonanno, A.; Corsaro, E.; Fletcher, S. T.; Gaulme, P.; Hekker, S.;
Karoff, C.; Régulo, C.; Salabert, D.; Verner, G. A.; White, T. R.;
Houdek, G.; Brandão, I. M.; Creevey, O. L.; Doǧan, G.; Bazot,
M.; Christensen-Dalsgaard, J.; Cunha, M. S.; Elsworth, Y.; Huber,
D.; Kjeldsen, H.; Lundkvist, M.; Molenda-Żakowicz, J.; Monteiro,
M. J. P. F. G.; Stello, D.; Clarke, B. D.; Girouard, F. R.; Hall, J. R.
2011A&A...534A...6C Altcode: 2011arXiv1108.3807C
Context. The evolved main-sequence Sun-like stars KIC 10273246 (F-type)
and KIC 10920273 (G-type) were observed with the NASA Kepler satellite
for approximately ten months with a duty cycle in excess of 90%. Such
continuous and long observations are unprecedented for solar-type
stars other than the Sun. <BR /> Aims: We aimed mainly at extracting
estimates of p-mode frequencies - as well as of other individual mode
parameters - from the power spectra of the light curves of both stars,
thus providing scope for a full seismic characterization. <BR />
Methods: The light curves were corrected for instrumental effects in
a manner independent of the Kepler science pipeline. Estimation of
individual mode parameters was based both on the maximization of the
likelihood of a model describing the power spectrum and on a classic
prewhitening method. Finally, we employed a procedure for selecting
frequency lists to be used in stellar modeling. <BR /> Results: A
total of 30 and 21 modes of degree l = 0,1,2 - spanning at least eight
radial orders - have been identified for KIC 10273246 and KIC 10920273,
respectively. Two avoided crossings (l = 1 ridge) have been identified
for KIC 10273246, whereas one avoided crossing plus another likely
one have been identified for KIC 10920273. Good agreement is found
between observed and predicted mode amplitudes for the F-type star KIC
10273246, based on a revised scaling relation. Estimates are given of
the rotational periods, the parameters describing stellar granulation
and the global asteroseismic parameters Δν and ν<SUB>max</SUB>.
---------------------------------------------------------
Title: An Asteroseismic Membership Study of the Red Giants in Three
Open Clusters Observed by Kepler: NGC 6791, NGC 6819, and NGC 6811
Authors: Stello, Dennis; Meibom, Søren; Gilliland, Ronald L.;
Grundahl, Frank; Hekker, Saskia; Mosser, Benoît; Kallinger, Thomas;
Mathur, Savita; García, Rafael A.; Huber, Daniel; Basu, Sarbani;
Bedding, Timothy R.; Brogaard, Karsten; Chaplin, William J.; Elsworth,
Yvonne P.; Molenda-Żakowicz, Joanna; Szabó, Robert; Still, Martin;
Jenkins, Jon M.; Christensen-Dalsgaard, Jørgen; Kjeldsen, Hans;
Serenelli, Aldo M.; Wohler, Bill
2011ApJ...739...13S Altcode: 2011arXiv1107.1234S
Studying star clusters offers significant advances in stellar
astrophysics due to the combined power of having many stars with
essentially the same distance, age, and initial composition. This
makes clusters excellent test benches for verification of stellar
evolution theory. To fully exploit this potential, it is vital that
the star sample is uncontaminated by stars that are not members of
the cluster. Techniques for determining cluster membership therefore
play a key role in the investigation of clusters. We present results
on three clusters in the Kepler field of view based on a newly
established technique that uses asteroseismology to identify fore-
or background stars in the field, which demonstrates advantages over
classical methods such as kinematic and photometry measurements. Four
previously identified seismic non-members in NGC 6819 are confirmed
in this study, and three additional non-members are found—two in
NGC 6819 and one in NGC 6791. We further highlight which stars are,
or might be, affected by blending, which needs to be taken into account
when analyzing these Kepler data.
---------------------------------------------------------
Title: The excitation of solar-like oscillations in a δSct star by
efficient envelope convection
Authors: Antoci, V.; Handler, G.; Campante, T. L.; Thygesen, A. O.;
Moya, A.; Kallinger, T.; Stello, D.; Grigahcène, A.; Kjeldsen, H.;
Bedding, T. R.; Lüftinger, T.; Christensen-Dalsgaard, J.; Catanzaro,
G.; Frasca, A.; De Cat, P.; Uytterhoeven, K.; Bruntt, H.; Houdek,
G.; Kurtz, D. W.; Lenz, P.; Kaiser, A.; van Cleve, J.; Allen, C.;
Clarke, B. D.
2011Natur.477..570A Altcode: 2011arXiv1109.4285A
Delta Scuti (δSct) stars are opacity-driven pulsators with masses
of 1.5-2.5M<SUB>solar</SUB>, their pulsations resulting from the
varying ionization of helium. In less massive stars such as the Sun,
convection transports mass and energy through the outer 30per cent of
the star and excites a rich spectrum of resonant acoustic modes. Based
on the solar example, with no firm theoretical basis, models predict
that the convective envelope in δSct stars extends only about 1per
cent of the radius, but with sufficient energy to excite solar-like
oscillations. This was not observed before the Kepler mission,
so the presence of a convective envelope in the models has been
questioned. Here we report the detection of solar-like oscillations
in the δSct star HD187547, implying that surface convection operates
efficiently in stars about twice as massive as the Sun, as the ad hoc
models predicted.
---------------------------------------------------------
Title: Verification of the Kepler Input Catalog from Asteroseismology
of Solar-type Stars
Authors: Verner, G. A.; Chaplin, W. J.; Basu, S.; Brown, T. M.;
Hekker, S.; Huber, D.; Karoff, C.; Mathur, S.; Metcalfe, T. S.;
Mosser, B.; Quirion, P. -O.; Appourchaux, T.; Bedding, T. R.; Bruntt,
H.; Campante, T. L.; Elsworth, Y.; García, R. A.; Handberg, R.;
Régulo, C.; Roxburgh, I. W.; Stello, D.; Christensen-Dalsgaard, J.;
Gilliland, R. L.; Kawaler, S. D.; Kjeldsen, H.; Allen, C.; Clarke,
B. D.; Girouard, F. R.
2011ApJ...738L..28V Altcode: 2011arXiv1109.0869V
We calculate precise stellar radii and surface gravities from the
asteroseismic analysis of over 500 solar-type pulsating stars observed
by the Kepler space telescope. These physical stellar properties
are compared with those given in the Kepler Input Catalog (KIC),
determined from ground-based multi-color photometry. For the stars
in our sample, we find general agreement but we detect an average
overestimation bias of 0.23 dex in the KIC determination of log (g)
for stars with log (g)<SUB>KIC</SUB> > 4.0 dex, and a resultant
underestimation bias of up to 50% in the KIC radii estimates for stars
with R <SUB>KIC</SUB> < 2 R <SUB>sun</SUB>. Part of the difference
may arise from selection bias in the asteroseismic sample; nevertheless,
this result implies there may be fewer stars characterized in the KIC
with R ~ 1 R <SUB>sun</SUB> than is suggested by the physical properties
in the KIC. Furthermore, if the radius estimates are taken from the
KIC for these affected stars and then used to calculate the size of
transiting planets, a similar underestimation bias may be applied to
the planetary radii.
---------------------------------------------------------
Title: ADIPLS: Aarhus Adiabatic Oscillation Package (ADIPACK)
Authors: Christensen-Dalsgaard, J.
2011ascl.soft09002C Altcode:
The goal of the development of the Aarhus Adiabatic Oscillation Package
was to have a simple and efficient tool for the computation of adiabatic
oscillation frequencies and eigenfunctions for general stellar models,
emphasizing also the accuracy of the results. The Fortran code offers
considerable flexibility in the choice of integration method as well
as ability to determine all frequencies of a given model, in a given
range of degree and frequency. Development of the Aarhus adiabatic
pulsation code started around 1978. Although the main features have been
stable for more than a decade, development of the code is continuing,
concerning numerical properties and output. The code has been provided
as a generally available package and has seen substantial use at a
number of installations. Further development of the package, including
bringing the documentation closer to being up to date, is planned as
part of the HELAS Coordination Action.
---------------------------------------------------------
Title: Amplitudes of Solar-like Oscillations: Constraints from Red
Giants in Open Clusters Observed by Kepler
Authors: Stello, Dennis; Huber, Daniel; Kallinger, Thomas; Basu,
Sarbani; Mosser, Benoît; Hekker, Saskia; Mathur, Savita; García,
Rafael A.; Bedding, Timothy R.; Kjeldsen, Hans; Gilliland, Ronald L.;
Verner, Graham A.; Chaplin, William J.; Benomar, Othman; Meibom,
Søren; Grundahl, Frank; Elsworth, Yvonne P.; Molenda-Żakowicz,
Joanna; Szabó, Robert; Christensen-Dalsgaard, Jørgen; Tenenbaum,
Peter; Twicken, Joseph D.; Uddin, Kamal
2011ApJ...737L..10S Altcode: 2011arXiv1107.0490S
Scaling relations that link asteroseismic quantities to global stellar
properties are important for gaining understanding of the intricate
physics that underpins stellar pulsations. The common notion that all
stars in an open cluster have essentially the same distance, age, and
initial composition implies that the stellar parameters can be measured
to much higher precision than what is usually achievable for single
stars. This makes clusters ideal for exploring the relation between
the mode amplitude of solar-like oscillations and the global stellar
properties. We have analyzed data obtained with NASA's Kepler space
telescope to study solar-like oscillations in 100 red giant stars
located in either of the three open clusters, NGC 6791, NGC 6819,
and NGC 6811. By fitting the measured amplitudes to predictions from
simple scaling relations that depend on luminosity, mass, and effective
temperature, we find that the data cannot be described by any power
of the luminosity-to-mass ratio as previously assumed. As a result
we provide a new improved empirical relation which treats luminosity
and mass separately. This relation turns out to also work remarkably
well for main-sequence and subgiant stars. In addition, the measured
amplitudes reveal the potential presence of a number of previously
unknown unresolved binaries in the red clump in NGC 6791 and NGC 6819,
pointing to an interesting new application for asteroseismology as a
probe into the formation history of open clusters.
---------------------------------------------------------
Title: Non-Blazhko RR Lyrae Stars Observed with the KEPLER Space
Telescope
Authors: Nemec, J. M.; Smolec, R.; Benko, J. M.; Moskalik, P.;
Kolenberg, K.; Szabó, R.; Kurtz, D. W.; Bryson, S.; Guggenberger,
E.; Chadid, M.; Jeon, Y. -B.; Kunder, A.; Layden, A. C.; Kinemuchi,
K.; Kiss, L. L.; Poretti, E.; Christensen-Dalsgaard, J.; Kjeldsen,
H.; Caldwell, D.; Ripepi, V.; Derekas, A.; Nuspl, J.; Mullally, F.;
Thompson, S. E.; Borucki, W. J.
2011rrls.conf...84N Altcode: 2011arXiv1108.5683N
This paper summarizes the main results of our recent study of
the non-Blazhko RR Lyrae stars observed with the Kepler space
telescope. These stars offer the opportunity for studying the stability
of the pulsations of RR Lyrae stars and for providing a reference
against which the Blazhko RR Lyrae stars can be compared. Of particular
interest is the stationarity of the low-dispersion (σ < 1mmag)
light curves constructed from ∼18000 long-cadence (30-min) and (for
FN Lyr and AW Dra) the ∼150000 short-cadence (1-min) photometric data
points. Fourier-based [Fe/H] values and other physical characteristics
are also derived. When the observed periods are compared with periods
computed with the Warsaw non-linear convective pulsation code better
agreement is achieved assuming pulsational L and M values rather than
the (higher) evolutionary L and M values.
---------------------------------------------------------
Title: Using SONG to probe rapid variability and evolution of
starspots
Authors: Neff, James E.; Hakkila, Jon; Hill, Frank; Jackiewicz, Jason;
Metcalfe, Travis S.; Christensen-Dalsgaard, Jørgen; Frandsen, Søren;
Grundahl, Frank; Kjeldsen, Hans; Jørgensen, Uffe Gråe; Rasmussen,
Per Kjærgaard; Gu, Sheng-Hong
2011IAUS..273..451N Altcode:
The Stellar Observations Network Group (SONG) is being developed
as a network of 1-meter spectroscopic telescopes designed for and
primarily dedicated to asteroseismology. It is patterned after the
highly successful GONG project. The Danish prototype telescope will
be installed in Tenerife in early 2011. Ultimately we hope to have
as many as 8 identical nodes providing continuous high-resolution
spectroscopic observations for targets anywhere in the sky. The
primary scientific goals of SONG are asteroseismology and the search
for Earth-mass exoplanets. The spectroscopic requirements for these
programs push the limits of current technology, but the resulting
spectrograph design will enable many secondary science programs
with less stringent requirements. Doppler imaging of starspots can
be accomplished using continuous observations over several stellar
rotations using identical instrumentation at each node. It should be
possible to observe the evolution of starspot morphology in real-time,
for example. We discuss the design and status of the SONG project
in general, and we describe how SONG could be used to probe short
timescale changes in stellar surface structure.
---------------------------------------------------------
Title: Stellar hydrodynamics caught in the act: Asteroseismology
with CoRoT and Kepler
Authors: Christensen-Dalsgaard, Jørgen; Thompson, Michael J.
2011IAUS..271...32C Altcode: 2011arXiv1104.5191C
Asteroseismic investigations, particularly based on data on stellar
oscillations from the CoRoT and Kepler space missions, are providing
unique possibilities for investigating the properties of stellar
interiors. This constitutes entirely new ways to study the effects
of dynamic phenomena on stellar structure and evolution. Important
examples are the extent of convection zones and the associated mixing
and the direct and indirect effects of stellar rotation. In addition,
the stellar oscillations themselves show very interesting dynamic
behaviour. Here we discuss examples of the results obtained from such
investigations, across the Hertzsprung-Russell diagram.
---------------------------------------------------------
Title: Solar-like oscillations from the depths of the red-giant star
KIC 4351319 observed with Kepler
Authors: di Mauro, M. P.; Cardini, D.; Catanzaro, G.; Ventura, R.;
Barban, C.; Bedding, T. R.; Christensen-Dalsgaard, J.; De Ridder,
J.; Hekker, S.; Huber, D.; Kallinger, T.; Miglio, A.; Montalban, J.;
Mosser, B.; Stello, D.; Uytterhoeven, K.; Kinemuchi, K.; Kjeldsen,
H.; Mullally, F.; Still, M.
2011MNRAS.415.3783D Altcode: 2011MNRAS.tmp.1166D; 2011arXiv1105.1076D
We present the results of the asteroseismic analysis of the red-giant
star KIC 4351319 (TYC 3124-914-1), observed for 30 d in short-cadence
mode with the Kepler satellite. The analysis has allowed us to determine
the large and small frequency separations, ?Hz and ?Hz, respectively,
and the frequency of maximum oscillation power, ?Hz. <P />The high
signal-to-noise ratio of the observations allowed us to identify 25
independent pulsation modes whose frequencies range approximately from
300 to ?Hz. <P />The observed oscillation frequencies together with
the accurate determination of the atmospheric parameters (effective
temperature, gravity and metallicity), provided by additional
ground-based spectroscopic observations, enabled us to theoretically
interpret the observed oscillation spectrum. <P />KIC 4351319 appears
to oscillate with a well-defined solar-type p-mode pattern due to radial
acoustic modes and non-radial nearly pure p modes. In addition, several
non-radial mixed modes have been identified. <P />Theoretical models
well reproduce the observed oscillation frequencies and indicate that
this star, located at the base of the ascending red-giant branch, is in
the hydrogen-shell-burning phase, with a mass of ∼1.3 M<SUB>⊙</SUB>,
a radius of ? and an age of ∼5.6 Gyr. The main parameters of this
star have been determined with an unprecedented level of precision
for a red-giant star, with uncertainties of 2 per cent for mass,
7 per cent for age, 1 per cent for radius and 4 per cent for luminosity.
---------------------------------------------------------
Title: Characteristics of Planetary Candidates Observed by
Kepler. II. Analysis of the First Four Months of Data
Authors: Borucki, William J.; Koch, David G.; Basri, Gibor; Batalha,
Natalie; Brown, Timothy M.; Bryson, Stephen T.; Caldwell, Douglas;
Christensen-Dalsgaard, Jørgen; Cochran, William D.; DeVore, Edna;
Dunham, Edward W.; Gautier, Thomas N., III; Geary, John C.; Gilliland,
Ronald; Gould, Alan; Howell, Steve B.; Jenkins, Jon M.; Latham, David
W.; Lissauer, Jack J.; Marcy, Geoffrey W.; Rowe, Jason; Sasselov,
Dimitar; Boss, Alan; Charbonneau, David; Ciardi, David; Doyle,
Laurance; Dupree, Andrea K.; Ford, Eric B.; Fortney, Jonathan; Holman,
Matthew J.; Seager, Sara; Steffen, Jason H.; Tarter, Jill; Welsh,
William F.; Allen, Christopher; Buchhave, Lars A.; Christiansen,
Jessie L.; Clarke, Bruce D.; Das, Santanu; Désert, Jean-Michel;
Endl, Michael; Fabrycky, Daniel; Fressin, Francois; Haas, Michael;
Horch, Elliott; Howard, Andrew; Isaacson, Howard; Kjeldsen, Hans;
Kolodziejczak, Jeffery; Kulesa, Craig; Li, Jie; Lucas, Philip W.;
Machalek, Pavel; McCarthy, Donald; MacQueen, Phillip; Meibom, Søren;
Miquel, Thibaut; Prsa, Andrej; Quinn, Samuel N.; Quintana, Elisa V.;
Ragozzine, Darin; Sherry, William; Shporer, Avi; Tenenbaum, Peter;
Torres, Guillermo; Twicken, Joseph D.; Van Cleve, Jeffrey; Walkowicz,
Lucianne; Witteborn, Fred C.; Still, Martin
2011ApJ...736...19B Altcode: 2011arXiv1102.0541B
On 2011 February 1 the Kepler mission released data for 156,453
stars observed from the beginning of the science observations on
2009 May 2 through September 16. There are 1235 planetary candidates
with transit-like signatures detected in this period. These are
associated with 997 host stars. Distributions of the characteristics
of the planetary candidates are separated into five class sizes:
68 candidates of approximately Earth-size (R <SUB>p</SUB> <
1.25 R <SUB>⊕</SUB>), 288 super-Earth-size (1.25 R <SUB>⊕</SUB>
<= R <SUB>p</SUB> < 2 R <SUB>⊕</SUB>), 662 Neptune-size
(2 R <SUB>⊕</SUB> <= R <SUB>p</SUB> < 6 R <SUB>⊕</SUB>),
165 Jupiter-size (6 R <SUB>⊕</SUB> <= R <SUB>p</SUB> <
15 R <SUB>⊕</SUB>), and 19 up to twice the size of Jupiter (15 R
<SUB>⊕</SUB> <= R <SUB>p</SUB> < 22 R <SUB>⊕</SUB>). In the
temperature range appropriate for the habitable zone, 54 candidates
are found with sizes ranging from Earth-size to larger than that
of Jupiter. Six are less than twice the size of the Earth. Over 74%
of the planetary candidates are smaller than Neptune. The observed
number versus size distribution of planetary candidates increases to a
peak at two to three times the Earth-size and then declines inversely
proportional to the area of the candidate. Our current best estimates
of the intrinsic frequencies of planetary candidates, after correcting
for geometric and sensitivity biases, are 5% for Earth-size candidates,
8% for super-Earth-size candidates, 18% for Neptune-size candidates,
2% for Jupiter-size candidates, and 0.1% for very large candidates; a
total of 0.34 candidates per star. Multi-candidate, transiting systems
are frequent; 17% of the host stars have multi-candidate systems,
and 34% of all the candidates are part of multi-candidate systems.
---------------------------------------------------------
Title: First Kepler results on compact pulsators - VI. Targets in
the final half of the survey phase
Authors: Østensen, R. H.; Silvotti, R.; Charpinet, S.; Oreiro, R.;
Bloemen, S.; Baran, A. S.; Reed, M. D.; Kawaler, S. D.; Telting, J. H.;
Green, E. M.; O'Toole, S. J.; Aerts, C.; Gänsicke, B. T.; Marsh,
T. R.; Breedt, E.; Heber, U.; Koester, D.; Quint, A. C.; Kurtz, D. W.;
Rodríguez-López, C.; Vučković, M.; Ottosen, T. A.; Frimann, S.;
Somero, A.; Wilson, P. A.; Thygesen, A. O.; Lindberg, J. E.; Kjeldsen,
H.; Christensen-Dalsgaard, J.; Allen, C.; McCauliff, S.; Middour, C. K.
2011MNRAS.414.2860O Altcode: 2011arXiv1101.4150O; 2011MNRAS.tmp..850O
We present results from the final 6 months of a survey to search
for pulsations in white dwarfs (WDs) and hot subdwarf stars with the
Kepler spacecraft. Spectroscopic observations are used to separate the
objects into accurate classes, and we explore the physical parameters
of the subdwarf B (sdB) stars and white dwarfs in the sample. From
the Kepler photometry and our spectroscopic data, we find that the
sample contains five new pulsators of the V1093 Her type, one AM CVn
type cataclysmic variable and a number of other binary systems. <P
/>This completes the survey for compact pulsators with Kepler. No
V361 Hya type of short-period pulsating sdB stars were found in
this half, leaving us with a total of one single multiperiodic V361
Hya and 13 V1093 Her pulsators for the full survey. Except for the
sdB pulsators, no other clearly pulsating hot subdwarfs or white
dwarfs were found, although a few low-amplitude candidates still
remain. The most interesting targets discovered in this survey will
be observed throughout the remainder of the Kepler mission, providing
the most long-term photometric data sets ever made on such compact,
evolved stars. Asteroseismic investigations of these data sets will
be invaluable in revealing the interior structure of these stars and
will boost our understanding of their evolutionary history.
---------------------------------------------------------
Title: The High Albedo of the Hot Jupiter Kepler-7 b
Authors: Demory, Brice-Olivier; Seager, Sara; Madhusudhan, Nikku;
Kjeldsen, Hans; Christensen-Dalsgaard, Jørgen; Gillon, Michaël;
Rowe, Jason F.; Welsh, William F.; Adams, Elisabeth R.; Dupree, Andrea;
McCarthy, Don; Kulesa, Craig; Borucki, William J.; Koch, David G.
2011ApJ...735L..12D Altcode: 2011arXiv1105.5143D
Hot Jupiters are expected to be dark from both observations
(albedo upper limits) and theory (alkali metals and/or TiO and
VO absorption). However, only a handful of hot Jupiters have been
observed with high enough photometric precision at visible wavelengths
to investigate these expectations. The NASA Kepler mission provides
a means to widen the sample and to assess the extent to which hot
Jupiter albedos are low. We present a global analysis of Kepler-7 b
based on Q0-Q4 data, published radial velocities, and asteroseismology
constraints. We measure an occultation depth in the Kepler bandpass
of 44 ± 5 ppm. If directly related to the albedo, this translates
to a Kepler geometric albedo of 0.32 ± 0.03, the most precise value
measured so far for an exoplanet. We also characterize the planetary
orbital phase light curve with an amplitude of 42 ± 4 ppm. Using
atmospheric models, we find it unlikely that the high albedo is due to
a dominant thermal component and propose two solutions to explain the
observed planetary flux. First, we interpret the Kepler-7 b albedo as
resulting from an excess reflection over what can be explained solely
by Rayleigh scattering, along with a nominal thermal component. This
excess reflection might indicate the presence of a cloud or haze
layer in the atmosphere, motivating new modeling and observational
efforts. Alternatively, the albedo can be explained by Rayleigh
scattering alone if Na and K are depleted in the atmosphere by a factor
of 10-100 below solar abundances.
---------------------------------------------------------
Title: First Kepler results on compact pulsators - VIII. Mode
identifications via period spacings in g-mode pulsating subdwarf
B stars
Authors: Reed, M. D.; Baran, A.; Quint, A. C.; Kawaler, S. D.; O'Toole,
S. J.; Telting, J.; Charpinet, S.; Rodríguez-López, C.; Østensen,
R. H.; Provencal, J. L.; Johnson, E. S.; Thompson, S. E.; Allen, C.;
Middour, C. K.; Kjeldsen, H.; Christensen-Dalsgaard, J.
2011MNRAS.414.2885R Altcode: 2011arXiv1102.4286R; 2011MNRAS.tmp..852R
We investigate the possibility of nearly equally spaced periods in
13 hot subdwarf B (sdB) stars observed with the Kepler spacecraft
and one observed with CoRoT. Asymptotic limits for gravity (g-)mode
pulsations provide relationships between equal-period spacings of
modes with differing degrees ℓ and relationships between periods of
the same radial order n but differing degrees ℓ. Period transforms,
Kolmogorov-Smirnov tests and linear least-squares fits have been used
to detect and determine the significance of equal-period spacings. We
have also used Monte Carlo simulations to estimate the likelihood that
the detected spacings could be produced randomly. <P />Period transforms
for nine of the Kepler stars indicate ℓ= 1 period spacings, with five
also showing peaks for ℓ= 2 modes. 12 stars indicate ℓ= 1 modes
using the Kolmogorov-Smirnov test while another shows solely ℓ=
2 modes. Monte Carlo results indicate that equal-period spacings are
significant in 10 stars above 99 per cent confidence, and 13 of the 14
are above 94 per cent confidence. For 12 stars, the various methods
find consistent period spacings to within the errors, two others
show some inconsistencies, likely caused by binarity, and the last
has significant detections but the mode assignment disagrees between
the methods. <P />We use asymptotic period spacing relationships to
associate observed periods of variability with pulsation modes for ℓ=
1 and 2. From the Kepler first-year survey sample of 13 multiperiodic
g-mode pulsators, five stars have several consecutive overtones making
period spacings easy to detect, six others have fewer consecutive
overtones but period spacings are readily detected, and two stars
show marginal indications of equal-period spacings. We also examine a
g-mode sdB pulsator observed by CoRoT with a rich pulsation spectrum,
and our tests detect regular period spacings. <P />We use Monte
Carlo simulations to estimate the significance of the detections in
individual stars. From the simulations, it is determined that regular
period spacings in 10 of the 14 stars are very unlikely to be random,
another two are moderately unlikely to be random and two are mostly
unconstrained. <P />We find a common ℓ= 1 period spacing spanning a
range from 231 to 272 s allowing us to correlate pulsation modes with
222 periodicities and that the ℓ= 2 period spacings are related
to the ℓ= 1 spacings by the asymptotic relationship ?. We briefly
discuss the impact of equal-period spacings which indicate low-degree
modes with a lack of significant mode trappings.
---------------------------------------------------------
Title: Kepler photometry of KIC 10661783: a binary star with total
eclipses and δ Scuti pulsations
Authors: Southworth, John; Zima, W.; Aerts, C.; Bruntt, H.; Lehmann,
H.; Kim, S. -L.; Kurtz, D. W.; Pavlovski, K.; Prša, A.; Smalley,
B.; Gilliland, R. L.; Christensen-Dalsgaard, J.; Kawaler, S. D.;
Kjeldsen, H.; Cote, M. T.; Tenenbaum, P.; Twicken, J. D.
2011MNRAS.414.2413S Altcode: 2011MNRAS.tmp..507S; 2011arXiv1102.3599S
We present Kepler satellite photometry of KIC 10661783, a short-period
binary star system which shows total eclipses and multiperiodic δ Scuti
pulsations. A frequency analysis of the eclipse-subtracted light curve
reveals at least 68 frequencies, of which 55 or more can be attributed
to pulsation modes. The main limitation on this analysis is the
frequency resolution within the 27-d short-cadence light curve. Most of
the variability signal lies in the frequency range 18-31 d<SUP>-1</SUP>,
with amplitudes between 0.1 and 4 mmag. One harmonic term (2f) and a
few combination frequencies (f<SUB>i</SUB>+f<SUB>j</SUB>) have been
detected. From a plot of the residuals versus orbital phase, we assign
the pulsations to the primary star in the system. The pulsations were
removed from the short-cadence data and the light curve was modelled
using the Wilson-Devinney code. We are unable to get a perfect fit
due to the residual effects of pulsations and also to the treatment
of reflection and reprocessing in the light-curve model. A model
where the secondary star fills its Roche lobe is favoured, which
means that KIC 10661783 can be classified as an oEA system. Further
photometric and spectroscopic observations will allow the masses and
radii of the two stars to be measured to high precision and hundreds
of δ Scuti pulsation frequencies to be resolved. This could lead to
unique constraints on theoretical models of δ Scuti stars, if the
evolutionary history of KIC 10661783 can be accounted for.
---------------------------------------------------------
Title: The first evidence for multiple pulsation axes: a new rapidly
oscillating Ap star in the Kepler field, KIC 10195926
Authors: Kurtz, D. W.; Cunha, M. S.; Saio, H.; Bigot, L.; Balona,
L. A.; Elkin, V. G.; Shibahashi, H.; Brandão, I. M.; Uytterhoeven,
K.; Frandsen, S.; Frimann, S.; Hatzes, A.; Lueftinger, T.; Gruberbauer,
M.; Kjeldsen, H.; Christensen-Dalsgaard, J.; Kawaler, S. D.
2011MNRAS.414.2550K Altcode: 2011arXiv1102.4298K; 2011MNRAS.tmp..558K
We have discovered a new rapidly oscillating Ap (roAp) star among
the Kepler mission target stars, KIC 10195926. This star shows two
pulsation modes with periods that are amongst the longest known for
roAp stars at 17.1 and 18.1 min, indicating that the star is near the
terminal-age main sequence. The principal pulsation mode is an oblique
dipole mode that shows a rotationally split frequency septuplet that
provides information on the geometry of the mode. The secondary mode
also appears to be a dipole mode with a rotationally split triplet,
but we are able to show within the improved oblique pulsator model
that these two modes cannot have the same axis of pulsation. This is
the first time for any pulsating star that evidence has been found for
separate pulsation axes for different modes. The two modes are separated
in frequency by 55 μHz, which we model as the large separation. The
star is an α<SUP>2</SUP> CVn spotted magnetic variable that shows a
complex rotational light variation with a period of P<SUB>rot</SUB>=
5.684 59 d. For the first time for any spotted magnetic star of the
upper main sequence, we find clear evidence of light variation with a
period of twice the rotation period, that is, a subharmonic frequency
of ν<SUB>rot</SUB>/2. We propose that this and other subharmonics
are the first observed manifestation of torsional modes in an roAp
star. From high-resolution spectra, we determine T<SUB>eff</SUB>=
7400 K, log g= 3.6 and v sin i= 21 km s<SUP>-1</SUP>. We have found
a magnetic pulsation model with fundamental parameters close to
these values that reproduces the rotational variations of the two
obliquely pulsating modes with different pulsation axes. The star
shows overabundances of the rare earth elements, but these are not
as extreme as most other roAp stars. The spectrum is variable with
rotation, indicating surface abundance patches.
---------------------------------------------------------
Title: First Kepler results on compact pulsators - VII. Pulsating
subdwarf B stars detected in the second half of the survey phase
Authors: Baran, A. S.; Kawaler, S. D.; Reed, M. D.; Quint, A. C.;
O'Toole, S. J.; Østensen, R. H.; Telting, J. H.; Silvotti, R.;
Charpinet, S.; Christensen-Dalsgaard, J.; Still, M.; Hall, J. R.;
Uddin, K.
2011MNRAS.414.2871B Altcode: 2011arXiv1103.1666B; 2011MNRAS.tmp..851B
We present five new pulsating subdwarf B (sdB) stars discovered by
the Kepler spacecraft during the asteroseismology survey phase. We
perform time series analysis on the nearly continuous month-long
Kepler data sets of these five objects; these data sets provide nearly
alias-free time series photometry at unprecedented precision. Following
an iterative pre-whitening process, we derive the pulsational frequency
spectra of these stars, separating out artefacts of known instrumental
origin. We find that these new pulsating sdB stars are multiperiodic
long-period pulsators of the V1093 Her type, with the number of
periodicities ranging from eight (KIC 8302197) to 53 (KIC 11558725). The
frequencies and amplitudes are typical of g-mode pulsators of this
type. We do not find any evidence for binarity in the five stars from
their observed pulsation frequencies. As these are g-mode pulsators,
we briefly looked for period spacings for mode identification and found
average spacings of about 260 and 145 s. This may indicate l= 1 and 2
patterns. Some modes may show evidence of rotational splitting. These
discoveries complete the list of compact pulsators found in the survey
phase. Of the 13 compact pulsators, only one star was identified as a
short-period (p-mode) V361 Hya pulsator, while all other new pulsators
turned out to be V1093 Her class objects. Among the latter objects, two
of them seemed to be pure V1093 Her while the others show additional
low-amplitude peaks in the p-mode frequency range, suggesting their
hybrid nature. Authenticity of these peaks will be tested with longer
runs currently under analysis.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Variability of A- and F-stars
from Kepler (Uytterhoeven+ 2011)
Authors: Uytterhoeven, K.; Moya, A.; Grigahcene, A.; Guzik, J. A.;
Gutierrez-Soto, J.; Smalley, B.; Handler, G.; Balona, L. A.; Niemczura,
E.; Fox Machado, L.; Benatti, S.; Chapellier, E.; Tkachenko, A.; Szabo,
R.; Suarez, J. C.; Ripepi, V.; Pascual, J.; Mathias, P.; Martin-Ruiz,
S.; Lehmann, H.; Jackiewicz, J.; Hekker, S.; Gruberbauer, M.; Garcia,
R. A.; Dumusque, X.; Diaz-Fraile, D.; Bradley, P.; Antoci, V.; Roth,
M.; Leroy, B.; Murphy, S. J.; De Cat, P.; Cuypers, J.; Kjeldsen, H.;
Christensen-Dalsgaard, J.; Breger, M.; Pigulski, A.; Kiss, L. L.;
Still, M.; Thompson, S. E.; van Cleve, J.
2011yCat..35340125U Altcode: 2011yCat..35349125U
We compile a database of physical parameters for the sample stars from
the literature and new ground-based observations. We analyse the Kepler
light curve of each star and extract the pulsational frequencies using
different frequency analysis methods. We construct two new observables,
'energy' and 'efficiency', related to the driving energy of the
pulsation mode and the convective efficiency of the outer convective
zone, respectively. <P />(5 data files).
---------------------------------------------------------
Title: Cepheid investigations using the Kepler space telescope
Authors: Szabó, R.; Szabados, L.; Ngeow, C. -C.; Smolec, R.;
Derekas, A.; Moskalik, P.; Nuspl, J.; Lehmann, H.; Fżrész, G.;
Molenda-Żakowicz, J.; Bryson, S. T.; Henden, A. A.; Kurtz, D. W.;
Stello, D.; Nemec, J. M.; Benkő, J. M.; Berdnikov, L.; Bruntt,
H.; Evans, N. R.; Gorynya, N. A.; Pastukhova, E. N.; Simcoe, R. J.;
Grindlay, J. E.; Los, E. J.; Doane, A.; Laycock, S. G.; Mink, D. J.;
Champine, G.; Sliski, A.; Handler, G.; Kiss, L. L.; Kolláth, Z.;
Kovács, J.; Christensen-Dalsgaard, J.; Kjeldsen, H.; Allen, C.;
Thompson, S. E.; van Cleve, J.
2011MNRAS.413.2709S Altcode: 2011MNRAS.tmp..332S; 2011arXiv1101.2443S
We report results of initial work done on selected candidate
Cepheids to be observed with the Kepler space telescope. Prior to the
launch, 40 candidates were selected from previous surveys and data
bases. The analysis of the first 322 d of Kepler photometry, and recent
ground-based follow-up multicolour photometry and spectroscopy allowed
us to confirm that one of these stars, V1154 Cyg (KIC 7548061), is
indeed a 4.9-d Cepheid. Using the phase lag method, we show that this
star pulsates in the fundamental mode. New radial velocity data are
consistent with previous measurements, suggesting that a long-period
binary component is unlikely. No evidence is seen in the ultraprecise,
nearly uninterrupted Kepler photometry for non-radial or stochastically
excited modes at the micromagnitude level. The other candidates are not
Cepheids, but an interesting mix of possible spotted stars, eclipsing
systems and flare stars.
---------------------------------------------------------
Title: Solar-like Oscillations in KIC 11395018 and KIC 11234888 from
8 Months of Kepler Data
Authors: Mathur, S.; Handberg, R.; Campante, T. L.; García, R. A.;
Appourchaux, T.; Bedding, T. R.; Mosser, B.; Chaplin, W. J.; Ballot,
J.; Benomar, O.; Bonanno, A.; Corsaro, E.; Gaulme, P.; Hekker,
S.; Régulo, C.; Salabert, D.; Verner, G.; White, T. R.; Brandão,
I. M.; Creevey, O. L.; Doǧan, G.; Elsworth, Y.; Huber, D.; Hale,
S. J.; Houdek, G.; Karoff, C.; Metcalfe, T. S.; Molenda-Żakowicz,
J.; Monteiro, M. J. P. F. G.; Thompson, M. J.; Christensen-Dalsgaard,
J.; Gilliland, R. L.; Kawaler, S. D.; Kjeldsen, H.; Quintana, E. V.;
Sanderfer, D. T.; Seader, S. E.
2011ApJ...733...95M Altcode: 2011arXiv1103.4085M
We analyze the photometric short-cadence data obtained with the Kepler
mission during the first 8 months of observations of two solar-type
stars of spectral types G and F: KIC 11395018 and KIC 11234888,
respectively, the latter having a lower signal-to-noise ratio (S/N)
compared with the former. We estimate global parameters of the acoustic
(p) modes such as the average large and small frequency separations, the
frequency of the maximum of the p-mode envelope, and the average line
width of the acoustic modes. We were able to identify and to measure
22 p-mode frequencies for the first star and 16 for the second one
even though the S/N of these stars are rather low. We also derive some
information about the stellar rotation periods from the analyses of the
low-frequency parts of the power spectral densities. A model-independent
estimation of the mean density, mass, and radius is obtained using the
scaling laws. We emphasize the importance of continued observations
for the stars with low S/N for an improved characterization of the
oscillation modes. Our results offer a preview of what will be possible
for many stars with the long data sets obtained during the remainder
of the mission.
---------------------------------------------------------
Title: A more realistic representation of overshoot at the base of
the solar convective envelope as seen by helioseismology
Authors: Christensen-Dalsgaard, J.; Monteiro, M. J. P. F. G.; Rempel,
M.; Thompson, M. J.
2011MNRAS.414.1158C Altcode: 2011MNRAS.tmp..440C; 2011arXiv1102.0235C
The stratification near the base of the Sun's convective envelope
is governed by processes of convective overshooting and element
diffusion, and the region is widely believed to play a key role in
the solar dynamo. The stratification in that region gives rise to
a characteristic signal in the frequencies of solar p modes, which
has been used to determine the depth of the solar convection zone
and to investigate the extent of convective overshoot. Previous
helioseismic investigations have shown that the Sun's spherically
symmetric stratification in this region is smoother than that in a
standard solar model without overshooting, and have ruled out simple
models incorporating overshooting, which extend the region of adiabatic
stratification and have a more-or-less abrupt transition to subadiabatic
stratification at the edge of the overshoot region. In this paper we
consider physically motivated models which have a smooth transition
in stratification bridging the region from the lower convection zone
to the radiative interior beneath. We find that such a model is in
better agreement with the helioseismic data than a standard solar model.
---------------------------------------------------------
Title: Preparation of Kepler light curves for asteroseismic analyses
Authors: García, R. A.; Hekker, S.; Stello, D.; Gutiérrez-Soto,
J.; Handberg, R.; Huber, D.; Karoff, C.; Uytterhoeven, K.;
Appourchaux, T.; Chaplin, W. J.; Elsworth, Y.; Mathur, S.; Ballot,
J.; Christensen-Dalsgaard, J.; Gilliland, R. L.; Houdek, G.; Jenkins,
J. M.; Kjeldsen, H.; McCauliff, S.; Metcalfe, T.; Middour, C. K.;
Molenda-Zakowicz, J.; Monteiro, M. J. P. F. G.; Smith, J. C.; Thompson,
M. J.
2011MNRAS.414L...6G Altcode: 2011arXiv1103.0382G
The Kepler mission is providing photometric data of exquisite
quality for the asteroseismic study of different classes of pulsating
stars. These analyses place particular demands on the pre-processing
of the data, over a range of time-scales from minutes to months. Here,
we describe processing procedures developed by the Kepler Asteroseismic
Science Consortium to prepare light curves that are optimized for the
asteroseismic study of solar-like oscillating stars in which outliers,
jumps and drifts are corrected.
---------------------------------------------------------
Title: Regularities in frequency spacings of δ Scuti stars: the
Kepler star KIC 9700322
Authors: Breger, M.; Balona, L.; Lenz, P.; Hollek, J. K.; Kurtz, D. W.;
Catanzaro, G.; Marconi, M.; Pamyatnykh, A. A.; Smalley, B.; Suárez,
J. C.; Szabo, R.; Uytterhoeven, K.; Ripepi, V.; Christensen-Dalsgaard,
J.; Kjeldsen, H.; Fanelli, M. N.; Ibrahim, K. A.; Uddin, K.
2011MNRAS.414.1721B Altcode: 2010arXiv1012.4373B; 2011MNRAS.tmp..479B
In the faint star KIC 9700322 observed by the Kepler satellite, 76
frequencies with amplitudes from 14 to 29 000 ppm were detected. The
two dominant frequencies at 9.79 and 12.57 d<SUP>-1</SUP> (113.3 and
145.5 μHz), interpreted to be radial modes, are accompanied by a large
number of combination frequencies. A small additional modulation with
a 0.16 d<SUP>-1</SUP> frequency is also seen; this is interpreted to
be the rotation frequency of the star. The corresponding prediction
of slow rotation is confirmed by a spectrum from which v sin i=
19 ± 1 km s<SUP>-1</SUP> is obtained. The analysis of the spectrum
shows that the star is one of the coolest δ Sct variables. We also
determine T<SUB>eff</SUB> = 6700 ± 100 K and log g = 3.7 ± 0.1,
compatible with the observed frequencies of the radial modes. Normal
solar abundances are found. An ℓ= 2 frequency quintuplet is also
detected with a frequency separation consistent with predictions from
the measured rotation rate. A remarkable result is the absence of
additional independent frequencies down to an amplitude limit near
14 ppm, suggesting that the star is stable against most forms of
non-radial pulsation. A low-frequency peak at 2.7763 d<SUP>-1</SUP>
in KIC 9700322 is the frequency difference between the two dominant
modes and is repeated over and over in various frequency combinations
involving the two dominant modes. The relative phases of the combination
frequencies show a strong correlation with frequency, but the physical
significance of this result is not clear. Based on observations
obtained with the Hobby-Eberly Telescope, which is a joint project of
the University of Texas at Austin, the Pennsylvania State University,
Stanford University, Ludwig-Maximilians-Universität München and
Georg-August-Universität Göttingen.
---------------------------------------------------------
Title: Deep asteroseismic sounding of the compact hot B subdwarf
pulsator KIC02697388 from Kepler time series photometry
Authors: Charpinet, S.; Van Grootel, V.; Fontaine, G.; Green, E. M.;
Brassard, P.; Randall, S. K.; Silvotti, R.; Østensen, R. H.; Kjeldsen,
H.; Christensen-Dalsgaard, J.; Kawaler, S. D.; Clarke, B. D.; Li,
J.; Wohler, B.
2011A&A...530A...3C Altcode:
Context. Contemporary high precision photometry from space provided by
the Kepler and CoRoT satellites generates significant breakthroughs
in terms of exploiting the long-period, g-mode pulsating hot B
subdwarf (sdBV<SUB>s</SUB>) stars with asteroseismology. <BR /> Aims:
We present a detailed asteroseismic study of the sdBV<SUB>s</SUB>
star KIC02697388 monitored with Kepler, using the rich pulsation
spectrum uncovered during the ~27-day-long exploratory run Q2.3. <BR
/> Methods: We analyse new high-S/N spectroscopy of KIC02697388 using
appropriate NLTE model atmospheres to provide accurate atmospheric
parameters for this star. We also reanalyse the Kepler light curve
using standard prewhitening techniques. On this basis, we apply
a forward modelling technique using our latest generation of sdB
models. The simultaneous match of the independent periods observed in
KIC02697388 with those of models leads objectively to the identification
of the pulsation modes and, more importantly, to the determination of
some of the parameters of the star. <BR /> Results: The light curve
analysis reveals 43 independent frequencies that can be associated
with oscillation modes. All the modulations observed in this star
correspond to g-mode pulsations except one high-frequency signal,
which is typical of a p-mode oscillation. Although the presence of
this p-mode is surprising considering the atmospheric parameters that
we derive for this cool sdB star (T<SUB>eff</SUB> = 25 395 ± 227 K,
log g = 5.500 ± 0.031 (cgs), and log N(He) /N(H) = -2.767 ± 0.122),
we show that this mode can be accounted for particularly well by
our optimal seismic models, both in terms of frequency match and
nonadiabatic properties. The seismic analysis leads us to identify
two model solutions that can both account for the observed pulsation
properties of KIC02697388. Despite this remaining ambiguity, several
key parameters of the star can be derived with stringent constraints,
such as its mass, its H-rich envelope mass, its radius, and its
luminosity. We derive the properties of the core proposing that it is
a relatively young sdB star that has burnt less than ~34% (in mass) of
its central helium and has a relatively large mixed He/C/O core. This
latter measurement is in line with the trend already uncovered for
two other g-mode sdB pulsators analysed with asteroseismology and
suggests that extra mixing is occurring quite early in the evolution
of He cores on the horizontal branch. <BR /> Conclusions: Additional
monitoring with Kepler of this particularly interesting sdB star should
reveal the inner properties of KIC02697388 and provide important
information about the mode driving mechanism and the helium core
properties. <P />Tables 3 and 4 are available in electronic form at
<A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Asteroseismic inferences on red giants in open clusters NGC
6791, NGC 6819, and NGC 6811 using Kepler
Authors: Hekker, S.; Basu, S.; Stello, D.; Kallinger, T.; Grundahl,
F.; Mathur, S.; García, R. A.; Mosser, B.; Huber, D.; Bedding, T. R.;
Szabó, R.; De Ridder, J.; Chaplin, W. J.; Elsworth, Y.; Hale, S. J.;
Christensen-Dalsgaard, J.; Gilliland, R. L.; Still, M.; McCauliff,
S.; Quintana, E. V.
2011A&A...530A.100H Altcode: 2011arXiv1104.4393H
Context. Four open clusters are present in the Kepler field of view
and timeseries of nearly a year in length are now available. These
timeseries allow us to derive asteroseismic global oscillation
parameters of red-giant stars in the three open clusters NGC 6791, NGC
6819 and NGC 6811. From these parameters and effective temperatures,
we derive masses, radii and luminosities for the clusters as well as
field red giants. <BR /> Aims: We study the influence of evolution and
metallicity on the observed red-giant populations. <BR /> Methods: The
global oscillation parameters are derived using different published
methods and the effective temperatures are derived from 2MASS
colours. The observational results are compared with BaSTI evolution
models. <BR /> Results: We find that the mass has significant influence
on the asteroseismic quantities Δν vs. ν<SUB>max</SUB> relation,
while the influence of metallicity is negligible, under the assumption
that the metallicity does not affect the excitation/damping of the
oscillations. The positions of the stars in the H-R diagram depend on
both mass and metallicity. Furthermore, the stellar masses derived for
the field stars are bracketed by those of the cluster stars. <BR />
Conclusions: Both the mass and metallicity contribute to the observed
difference in locations in the H-R diagram of the old metal-rich cluster
NGC 6791 and the middle-aged solar-metallicity cluster NGC 6819. For
the young cluster NGC 6811, the explanation of the position of the stars
in the H-R diagram challenges the assumption of solar metallicity, and
this open cluster might have significantly lower metallicity [Fe/H]
in the range - 0.3 to - 0.7 dex. Also, nearly all the observed field
stars seem to be older than NGC 6811 and younger than NGC 6791.
---------------------------------------------------------
Title: Kepler observations of the variability in B-type stars
Authors: Balona, L. A.; Pigulski, A.; De Cat, P.; Handler, G.;
Gutiérrez-Soto, J.; Engelbrecht, C. A.; Frescura, F.; Briquet, M.;
Cuypers, J.; Daszyńska-Daszkiewicz, J.; Degroote, P.; Dukes, R. J.;
Garcia, R. A.; Green, E. M.; Heber, U.; Kawaler, S. D.; Lehmann,
H.; Leroy, B.; Molenda-Żaaowicz, J.; Neiner, C.; Noels, A.; Nuspl,
J.; Østensen, R.; Pricopi, D.; Roxburgh, I.; Salmon, S.; Smith,
M. A.; Suárez, J. C.; Suran, M.; Szabó, R.; Uytterhoeven, K.;
Christensen-Dalsgaard, J.; Kjeldsen, H.; Caldwell, D. A.; Girouard,
F. R.; Sanderfer, D. T.
2011MNRAS.413.2403B Altcode: 2011MNRAS.tmp..298B; 2011arXiv1103.0644B
The analysis of the light curves of 48 B-type stars observed by Kepler
is presented. Among these are 15 pulsating stars, all of which show low
frequencies, characteristic of slowly pulsating B (SPB) stars. Seven of
these stars also show a few weak, isolated high frequencies and they
could be considered as SPB/β Cephei (β Cep) hybrids. In all cases,
the frequency spectra are quite different from what is seen from
ground-based observations. We suggest that this is because most of
the low frequencies are modes of high degree which are predicted to be
unstable in models of mid-B stars. We find that there are non-pulsating
stars within the β Cep and SPB instability strips. Apart from the
pulsating stars, we can identify stars with frequency groupings similar
to what is seen in Be stars but which are not Be stars. The origin of
the groupings is not clear, but may be related to rotation. We find
periodic variations in other stars which we attribute to proximity
effects in binary systems or possibly rotational modulation. We find
no evidence for pulsating stars between the cool edge of the SPB
and the hot edge of the δ Sct instability strips. None of the stars
shows the broad features which can be attributed to stochastically
excited modes as recently proposed. Among our sample of B stars are
two chemically peculiar stars, one of which is a HgMn star showing
rotational modulation in the light curve.
---------------------------------------------------------
Title: Kepler observations of Am stars
Authors: Balona, L. A.; Ripepi, V.; Catanzaro, G.; Kurtz,
D. W.; Smalley, B.; De Cat, P.; Eyer, L.; Grigahcène, A.;
Leccia, S.; Southworth, J.; Uytterhoeven, K.; van Winckel, H.;
Christensen-Dalsgaard, J.; Kjeldsen, H.; Caldwell, D. A.; van Cleve,
J.; Girouard, F. R.
2011MNRAS.414..792B Altcode: 2011MNRAS.tmp..396B
We present an analysis of high-resolution spectra for two pulsating Am
stars in the Kepler field. The stellar parameters derived in this way
are important because parameters derived from narrow-band photometry
may be affected by the strong metal lines in these stars. We analyse
the Kepler time series of ten known Am stars and find that six of
them clearly show δ Scuti pulsations. The other four appear to
be non-pulsating. We derive fundamental parameters for all known
pulsating Am stars from ground-based observations and also for the
Kepler Am stars to investigate the location of the instability strip
for pulsating Am stars. We find that there is not much difference
between the Am-star instability strip and the δ Scuti instability
strip. We find that the observed location of pulsating Am stars in the
HR diagram does not agree with the location predicted from diffusion
calculations. Based on observations made with the Italian Telescopio
Nazionale Galileo (TNG) operated on the island of La Palma by the
Fondación Galileo Galilei of the Istituto Nazionale di Astrofisica
(INAF), at the Spanish Observatorio del Roque de los Muchachos of the
Instituto de Astrofisica de Canarias, and with the Mercator Telescope
operated on the island of La Palma by the Flemish Community.
---------------------------------------------------------
Title: Rotation and oblique pulsation in Kepler observations of the
roAp star KIC 10483436
Authors: Balona, L. A.; Cunha, M. S.; Gruberbauer, M.; Kurtz, D. W.;
Saio, H.; White, T. R.; Christensen-Dalsgaard, J.; Kjeldsen, H.;
Christiansen, J. L.; Hall, J. R.; Seader, S. E.
2011MNRAS.413.2651B Altcode: 2011MNRAS.tmp..526B
Photometry of KIC 10483436 was obtained continuously with 1-min
exposures over a 27-d period from the Kepler satellite. The light
curve shows rotational variations from surface spots with a period of
4.303 ± 0.002 d, an amplitude of about 6 mmag and eight pulsation
frequencies typical of roAp stars. The high-frequency pattern
consists of a quintuplet of equally spaced peaks where the frequency
of the dominant central peak (68 μmag amplitude) is 1353.00 μHz
(P= 12.32 min). A second set of three peaks of lower amplitude are
also visible. These appear to form part of a quintuplet centred on
1511.6 μHz with the central peak and one side peak missing. The
equidistant frequency spacing is 2.69 μHz, which corresponds to
the 4.303 d rotation period. However, the amplitudes (12 μmag) of
these peaks are too close to the detection level to allow definite
identification of the multiplets. Although no spectrum is available,
the character of the pulsations shows that this is a roAp star with
two high-frequency modes modulated in amplitude in accordance with
the oblique pulsator model. The 4.303-d variation in the light curve,
which is interpreted as rotational modulation, shows harmonics as high
as the 26th. These harmonics are probably a result of many patches of
varying surface brightness associated with surface abundance variations
characteristic of Ap stars.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Kepler compact pulsator candidates
(Ostensen+, 2010)
Authors: Ostensen, R. H.; Silvotti, R.; Charpinet, S.; Oreiro, R.;
Handler, G.; Green, E. M.; Bloemen, S.; Heber, U.; Gansicke, B. T.;
Marsh, T. R.; Kurtz, D. W.; Telting, J. H.; Reed, M. D.; Kawaler,
S. D.; Aerts, C.; Rodriguez-Lopez, C.; Vuckovic, M.; Ottosen, T. A.;
Liimets, T.; Quint, A. C.; Van Grootel, V.; Randall, S. K.; Gilliland,
R. L.; Kjeldsen, H.; Christensen-Dalsgaard, J.; Borucki, W. J.; Koch,
D.; Quintana, E. V.
2011yCat..74091470O Altcode:
For the survey phase of the Kepler Mission, three groups submitted
proposals containing candidate hot subdwarf and white dwarf stars. Of
the stars included in these proposals, 142 were accepted into the
list of KASC survey stars. Of these, six were observed during the
9.7d commissioning run, and 57 were observed during the first four
(out of 10) survey months. All 63 stars are listed in Table 1. <P />(1
data file).
---------------------------------------------------------
Title: VizieR Online Data Catalog: Solar-like oscillations in Kepler
red giants (Hekker+, 2011)
Authors: Hekker, S.; Elsworth, Y.; De Ridder, J.; Mosser, B.; Garcia,
R. A.; Kallinger, T.; Mathur, S.; Huber, D.; Buzasi, D. L.; Preston,
H. L.; Hale, S. J.; Ballot, J.; Chaplin, W. J.; Regulo, C.; Bedding,
T. R.; Stello, D.; Borucki, W. J.; Koch, D. G.; Jenkins, J.; Allen,
C.; Gilliland, R. L.; Kjeldsen, H.; Christensen-Dalsgaard, J.
2011yCat..35250131H Altcode: 2011yCat..35259131H
For this investigation we use Kepler data obtained during the first four
months of operation. These data have been analysed by different groups
using already published methods and the results are compared. We also
performed simulations to investigate the uncertainty on the resulting
parameters due to different realizations of the stochastic signal. <P
/>(1 data file).
---------------------------------------------------------
Title: Predicting the Detectability of Oscillations in Solar-type
Stars Observed by Kepler
Authors: Chaplin, W. J.; Kjeldsen, H.; Bedding, T. R.;
Christensen-Dalsgaard, J.; Gilliland, R. L.; Kawaler, S. D.;
Appourchaux, T.; Elsworth, Y.; García, R. A.; Houdek, G.; Karoff, C.;
Metcalfe, T. S.; Molenda-Żakowicz, J.; Monteiro, M. J. P. F. G.;
Thompson, M. J.; Verner, G. A.; Batalha, N.; Borucki, W. J.;
Brown, T. M.; Bryson, S. T.; Christiansen, J. L.; Clarke, B. D.;
Jenkins, J. M.; Klaus, T. C.; Koch, D.; An, D.; Ballot, J.; Basu,
S.; Benomar, O.; Bonanno, A.; Broomhall, A. -M.; Campante, T. L.;
Corsaro, E.; Creevey, O. L.; Esch, L.; Gai, N.; Gaulme, P.; Hale,
S. J.; Handberg, R.; Hekker, S.; Huber, D.; Mathur, S.; Mosser, B.;
New, R.; Pinsonneault, M. H.; Pricopi, D.; Quirion, P. -O.; Régulo,
C.; Roxburgh, I. W.; Salabert, D.; Stello, D.; Suran, M. D.
2011ApJ...732...54C Altcode: 2011arXiv1103.0702C
Asteroseismology of solar-type stars has an important part to play
in the exoplanet program of the NASA Kepler Mission. Precise and
accurate inferences on the stellar properties that are made possible
by the seismic data allow very tight constraints to be placed on the
exoplanetary systems. Here, we outline how to make an estimate of the
detectability of solar-like oscillations in any given Kepler target,
using rough estimates of the temperature and radius, and the Kepler
apparent magnitude.
---------------------------------------------------------
Title: Evidence for the Impact of Stellar Activity on the
Detectability of Solar-like Oscillations Observed by Kepler
Authors: Chaplin, W. J.; Bedding, T. R.; Bonanno, A.; Broomhall,
A. -M.; García, R. A.; Hekker, S.; Huber, D.; Verner, G. A.;
Basu, S.; Elsworth, Y.; Houdek, G.; Mathur, S.; Mosser, B.; New,
R.; Stevens, I. R.; Appourchaux, T.; Karoff, C.; Metcalfe, T. S.;
Molenda-Żakowicz, J.; Monteiro, M. J. P. F. G.; Thompson, M. J.;
Christensen-Dalsgaard, J.; Gilliland, R. L.; Kawaler, S. D.; Kjeldsen,
H.; Ballot, J.; Benomar, O.; Corsaro, E.; Campante, T. L.; Gaulme,
P.; Hale, S. J.; Handberg, R.; Jarvis, E.; Régulo, C.; Roxburgh,
I. W.; Salabert, D.; Stello, D.; Mullally, F.; Li, J.; Wohler, W.
2011ApJ...732L...5C Altcode: 2011arXiv1103.5570C
We use photometric observations of solar-type stars, made by the NASA
Kepler Mission, to conduct a statistical study of the impact of stellar
surface activity on the detectability of solar-like oscillations. We
find that the number of stars with detected oscillations falls
significantly with increasing levels of activity. The results present
strong evidence for the impact of magnetic activity on the properties
of near-surface convection in the stars, which appears to inhibit
the amplitudes of the stochastically excited, intrinsically damped
solar-like oscillations.
---------------------------------------------------------
Title: Large-scale Zonal Flows During the Solar Minimum -- Where Is
Cycle 25?
Authors: Hill, Frank; Howe, R.; Komm, R.; Christensen-Dalsgaard, J.;
Larson, T. P.; Schou, J.; Thompson, M. J.
2011SPD....42.1610H Altcode: 2011BAAS..43S.1610H
The so-called torsional oscillation is a pattern of migrating zonal flow
bands that move from mid-latitudes towards the equator and poles as the
magnetic cycle progresses. Helioseismology allows us to probe these
flows below the solar surface. The prolonged solar minimum following
Cycle 23 was accompanied by a delay of 1.5 to 2 years in the migration
of bands of faster rotation towards the equator. During the rising phase
of Cycle 24, while the lower-level bands match those seen in the rising
phase of Cycle 23, the rotation rate at middle and higher latitudes
remains slower than it was at the corresponding phase in earlier cycles,
perhaps reflecting the weakness of the polar fields. In addition,
there is no evidence of the poleward flow associated with Cycle 25. We
will present the latest results based on nearly sixteen years of global
helioseismic observations from GONG and MDI, with recent results from
HMI, and discuss the implications for the development of Cycle 25.
---------------------------------------------------------
Title: Ensemble Asteroseismology of Solar-Type Stars with the NASA
Kepler Mission
Authors: Chaplin, W. J.; Kjeldsen, H.; Christensen-Dalsgaard, J.;
Basu, S.; Miglio, A.; Appourchaux, T.; Bedding, T. R.; Elsworth, Y.;
García, R. A.; Gilliland, R. L.; Girardi, L.; Houdek, G.; Karoff,
C.; Kawaler, S. D.; Metcalfe, T. S.; Molenda-Żakowicz, J.; Monteiro,
M. J. P. F. G.; Thompson, M. J.; Verner, G. A.; Ballot, J.; Bonanno,
A.; Brandão, I. M.; Broomhall, A. -M.; Bruntt, H.; Campante, T. L.;
Corsaro, E.; Creevey, O. L.; Doğan, G.; Esch, L.; Gai, N.; Gaulme,
P.; Hale, S. J.; Handberg, R.; Hekker, S.; Huber, D.; Jiménez, A.;
Mathur, S.; Mazumdar, A.; Mosser, B.; New, R.; Pinsonneault, M. H.;
Pricopi, D.; Quirion, P. -O.; Régulo, C.; Salabert, D.; Serenelli,
A. M.; Silva Aguirre, V.; Sousa, S. G.; Stello, D.; Stevens, I. R.;
Suran, M. D.; Uytterhoeven, K.; White, T. R.; Borucki, W. J.; Brown,
T. M.; Jenkins, J. M.; Kinemuchi, K.; Van Cleve, J.; Klaus, T. C.
2011Sci...332..213C Altcode: 2011arXiv1109.4723C
In addition to its search for extrasolar planets, the NASA Kepler
mission provides exquisite data on stellar oscillations. We report the
detections of oscillations in 500 solar-type stars in the Kepler field
of view, an ensemble that is large enough to allow statistical studies
of intrinsic stellar properties (such as mass, radius, and age) and
to test theories of stellar evolution. We find that the distribution
of observed masses of these stars shows intriguing differences to
predictions from models of synthetic stellar populations in the Galaxy.
---------------------------------------------------------
Title: HD 181068: A Red Giant in a Triply Eclipsing Compact
Hierarchical Triple System
Authors: Derekas, A.; Kiss, L. L.; Borkovits, T.; Huber, D.; Lehmann,
H.; Southworth, J.; Bedding, T. R.; Balam, D.; Hartmann, M.; Hrudkova,
M.; Ireland, M. J.; Kovács, J.; Mező, Gy.; Moór, A.; Niemczura, E.;
Sarty, G. E.; Szabó, Gy. M.; Szabó, R.; Telting, J. H.; Tkachenko,
A.; Uytterhoeven, K.; Benkő, J. M.; Bryson, S. T.; Maestro, V.;
Simon, A. E.; Stello, D.; Schaefer, G.; Aerts, C.; ten Brummelaar,
T. A.; De Cat, P.; McAlister, H. A.; Maceroni, C.; Mérand, A.;
Still, M.; Sturmann, J.; Sturmann, L.; Turner, N.; Tuthill, P. G.;
Christensen-Dalsgaard, J.; Gilliland, R. L.; Kjeldsen, H.; Quintana,
E. V.; Tenenbaum, P.; Twicken, J. D.
2011Sci...332..216D Altcode: 2012arXiv1202.2196D
Hierarchical triple systems comprise a close binary and a more distant
component. They are important for testing theories of star formation
and of stellar evolution in the presence of nearby companions. We
obtained 218 days of Kepler photometry of HD 181068 (magnitude of
7.1), supplemented by ground-based spectroscopy and interferometry,
which show it to be a hierarchical triple with two types of mutual
eclipses. The primary is a red giant that is in a 45-day orbit with
a pair of red dwarfs in a close 0.9-day orbit. The red giant shows
evidence for tidally induced oscillations that are driven by the
orbital motion of the close pair. HD 181068 is an ideal target for
studies of dynamical evolution and testing tidal friction theories in
hierarchical triple systems.
---------------------------------------------------------
Title: Kepler Detected Gravity-Mode Period Spacings in a Red
Giant Star
Authors: Beck, P. G.; Bedding, T. R.; Mosser, B.; Stello, D.; Garcia,
R. A.; Kallinger, T.; Hekker, S.; Elsworth, Y.; Frandsen, S.; Carrier,
F.; De Ridder, J.; Aerts, C.; White, T. R.; Huber, D.; Dupret, M. -A.;
Montalbán, J.; Miglio, A.; Noels, A.; Chaplin, W. J.; Kjeldsen, H.;
Christensen-Dalsgaard, J.; Gilliland, R. L.; Brown, T. M.; Kawaler,
S. D.; Mathur, S.; Jenkins, J. M.
2011Sci...332..205B Altcode:
Stellar interiors are inaccessible through direct observations. For
this reason, helioseismologists made use of the Sun’s acoustic
oscillation modes to tune models of its structure. The quest to detect
modes that probe the solar core has been ongoing for decades. We
report the detection of mixed modes penetrating all the way to the
core of an evolved star from 320 days of observations with the Kepler
satellite. The period spacings of these mixed modes are directly
dependent on the density gradient between the core region and the
convective envelope.
---------------------------------------------------------
Title: VizieR Online Data Catalog: 2M1938+4603 (KIC 9472174) eclipses
(Ostensen+, 2010)
Authors: Ostensen, R. H.; Green, E. M.; Bloemen, S.; Marsh, T. R.;
Laird, J. B.; Morris, M.; Moriyama, E.; Oreiro, R.; Reed, M. D.;
Kawaler, S. D.; Aerts, C.; Vuckovic, M.; Degroote, P.; Telting, J. H.;
Kjeldsen, H.; Gilliland, R. L.; Christensen-Dalsgaard, J.; Borucki,
W. J.; Koch, D.
2011yCat..74089051O Altcode:
The discovery of the strong reflection effect with grazing eclipses
was made by two of us (JBL and MM) during a photometric run in 2008
June. Here we present only the eclipse timings from the ground-based
photometry, as the pulsations are too complex and have too low
amplitudes to be significant in those light curves. <P />(4 data files).
---------------------------------------------------------
Title: Sounding Open Clusters: Asteroseismic Constraints from Kepler
on the Properties of NGC 6791 and NGC 6819
Authors: Basu, Sarbani; Grundahl, Frank; Stello, Dennis; Kallinger,
Thomas; Hekker, Saskia; Mosser, Benoit; García, Rafael A.; Mathur,
Savita; Brogaard, Karsten; Bruntt, Hans; Chaplin, William J.; Gai,
Ning; Elsworth, Yvonne; Esch, Lisa; Ballot, Jerome; Bedding, Timothy
R.; Gruberbauer, Michael; Huber, Daniel; Miglio, Andrea; Yildiz, Mutlu;
Kjeldsen, Hans; Christensen-Dalsgaard, Jørgen; Gilliland, Ronald L.;
Fanelli, Michael M.; Ibrahim, Khadeejah A.; Smith, Jeffrey C.
2011ApJ...729L..10B Altcode: 2011arXiv1102.2231B
We present initial results on some of the properties of open clusters
NGC 6791 and NGC 6819 derived from asteroseismic data obtained by
NASA's Kepler mission. In addition to estimating the mass, radius,
and log g of stars on the red giant branch (RGB) of these clusters,
we estimate the distance to the clusters and their ages. Our
model-independent estimate of the distance modulus of NGC 6791 is
(m - M)<SUB>0</SUB> = 13.11 ± 0.06. We find (m - M)<SUB>0</SUB> =
11.85 ± 0.05 for NGC 6819. The average mass of stars on the RGB of
NGC 6791 is 1.20 ± 0.01 M <SUB>sun</SUB>, while that of NGC 6819 is
1.68 ± 0.03 M <SUB>sun</SUB>. It should be noted that we do not have
data that cover the entire RGB and the actual mass will be somewhat
lower. We have determined model-dependent estimates of ages of these
clusters. We find ages between 6.8 and 8.6 Gyr for NGC 6791, however,
most sets of models give ages around 7 Gyr. We obtain ages between 2
and 2.4 Gyr for NGC 6819.
---------------------------------------------------------
Title: Asteroseismic modelling of the solar-type subgiant star
β Hydri
Authors: Brandão, I. M.; Doğan, G.; Christensen-Dalsgaard, J.;
Cunha, M. S.; Bedding, T. R.; Metcalfe, T. S.; Kjeldsen, H.; Bruntt,
H.; Arentoft, T.
2011A&A...527A..37B Altcode: 2010arXiv1012.3872B
Context. Comparing models and data of pulsating stars is a powerful
way to understand the stellar structure better. Moreover, such
comparisons are necessary to make improvements to the physics of the
stellar models, since they do not yet perfectly represent either the
interior or especially the surface layers of stars. Because β Hydri
is an evolved solar-type pulsator with mixed modes in its frequency
spectrum, it is very interesting for asteroseismic studies. <BR /> Aims:
The goal of the present work is to search for a representative model
of the solar-type star β Hydri, based on up-to-date non-seismic and
seismic data. <BR /> Methods: We present a revised list of frequencies
for 33 modes, which we produced by analysing the power spectrum of the
published observations again using a new weighting scheme that minimises
the daily sidelobes. We ran several grids of evolutionary models with
different input parameters and different physics, using the stellar
evolutionary code ASTEC. For the models that are inside the observed
error box of β Hydri, we computed their frequencies with the pulsation
code ADIPLS. We used two approaches to find the model that oscillates
with the frequencies that are closest to the observed frequencies of
β Hydri: (i) we assume that the best model is the one that reproduces
the star's interior based on the radial oscillation frequencies alone,
to which we have applied the correction for the near-surface effects;
(ii) we assume that the best model is the one that produces the lowest
value of the chi-square (χ<SUP>2</SUP>), i.e. that minimises the
difference between the observed frequencies of all available modes
and the model predictions, after all model frequencies are corrected
for near-surface effects. <BR /> Results: We show that after applying
a correction for near-surface effects to the frequencies of the best
models, we can reproduce the observed modes well, including those
that have mixed mode character. The model that gives the lowest value
of the χ<SUP>2</SUP> is a post-main-sequence model with a mass of
1.04 M<SUB>⊙</SUB> and a metallicity slightly lower than that of
the Sun. Our results underscore the importance of having individual
frequencies to constrain the properties of the stellar model.
---------------------------------------------------------
Title: Gravity modes as a way to distinguish between hydrogen-
and helium-burning red giant stars
Authors: Bedding, Timothy R.; Mosser, Benoit; Huber, Daniel;
Montalbán, Josefina; Beck, Paul; Christensen-Dalsgaard, Jørgen;
Elsworth, Yvonne P.; García, Rafael A.; Miglio, Andrea; Stello,
Dennis; White, Timothy R.; De Ridder, Joris; Hekker, Saskia; Aerts,
Conny; Barban, Caroline; Belkacem, Kevin; Broomhall, Anne-Marie;
Brown, Timothy M.; Buzasi, Derek L.; Carrier, Fabien; Chaplin,
William J.; di Mauro, Maria Pia; Dupret, Marc-Antoine; Frandsen,
Søren; Gilliland, Ronald L.; Goupil, Marie-Jo; Jenkins, Jon M.;
Kallinger, Thomas; Kawaler, Steven; Kjeldsen, Hans; Mathur, Savita;
Noels, Arlette; Silva Aguirre, Victor; Ventura, Paolo
2011Natur.471..608B Altcode: 2011arXiv1103.5805B
Red giants are evolved stars that have exhausted the supply of hydrogen
in their cores and instead burn hydrogen in a surrounding shell. Once a
red giant is sufficiently evolved, the helium in the core also undergoes
fusion. Outstanding issues in our understanding of red giants include
uncertainties in the amount of mass lost at the surface before helium
ignition and the amount of internal mixing from rotation and other
processes. Progress is hampered by our inability to distinguish between
red giants burning helium in the core and those still only burning
hydrogen in a shell. Asteroseismology offers a way forward, being
a powerful tool for probing the internal structures of stars using
their natural oscillation frequencies. Here we report observations of
gravity-mode period spacings in red giants that permit a distinction
between evolutionary stages to be made. We use high-precision
photometry obtained by the Kepler spacecraft over more than a year
to measure oscillations in several hundred red giants. We find many
stars whose dipole modes show sequences with approximately regular
period spacings. These stars fall into two clear groups, allowing us
to distinguish unambiguously between hydrogen-shell-burning stars
(period spacing mostly ~50seconds) and those that are also burning
helium (period spacing ~100 to 300 seconds).
---------------------------------------------------------
Title: Kepler's First Rocky Planet: Kepler-10b
Authors: Batalha, Natalie M.; Borucki, William J.; Bryson, Stephen
T.; Buchhave, Lars A.; Caldwell, Douglas A.; Christensen-Dalsgaard,
Jørgen; Ciardi, David; Dunham, Edward W.; Fressin, Francois;
Gautier, Thomas N., III; Gilliland, Ronald L.; Haas, Michael R.;
Howell, Steve B.; Jenkins, Jon M.; Kjeldsen, Hans; Koch, David G.;
Latham, David W.; Lissauer, Jack J.; Marcy, Geoffrey W.; Rowe, Jason
F.; Sasselov, Dimitar D.; Seager, Sara; Steffen, Jason H.; Torres,
Guillermo; Basri, Gibor S.; Brown, Timothy M.; Charbonneau, David;
Christiansen, Jessie; Clarke, Bruce; Cochran, William D.; Dupree,
Andrea; Fabrycky, Daniel C.; Fischer, Debra; Ford, Eric B.; Fortney,
Jonathan; Girouard, Forrest R.; Holman, Matthew J.; Johnson, John;
Isaacson, Howard; Klaus, Todd C.; Machalek, Pavel; Moorehead, Althea
V.; Morehead, Robert C.; Ragozzine, Darin; Tenenbaum, Peter; Twicken,
Joseph; Quinn, Samuel; VanCleve, Jeffrey; Walkowicz, Lucianne M.;
Welsh, William F.; Devore, Edna; Gould, Alan
2011ApJ...729...27B Altcode: 2011arXiv1102.0605B
NASA's Kepler Mission uses transit photometry to determine
the frequency of Earth-size planets in or near the habitable
zone of Sun-like stars. The mission reached a milestone toward
meeting that goal: the discovery of its first rocky planet,
Kepler-10b. Two distinct sets of transit events were detected: (1)
a 152 ± 4 ppm dimming lasting 1.811 ± 0.024 hr with ephemeris
T [BJD] =2454964.57375<SUP>+0.00060</SUP> <SUB>-0.00082</SUB> +
N*0.837495<SUP>+0.000004</SUP> <SUB>-0.000005</SUB> days and (2)
a 376 ± 9 ppm dimming lasting 6.86 ± 0.07 hr with ephemeris
T [BJD] =2454971.6761<SUP>+0.0020</SUP> <SUB>-0.0023</SUB> +
N*45.29485<SUP>+0.00065</SUP> <SUB>-0.00076</SUB> days. Statistical
tests on the photometric and pixel flux time series established the
viability of the planet candidates triggering ground-based follow-up
observations. Forty precision Doppler measurements were used to confirm
that the short-period transit event is due to a planetary companion. The
parent star is bright enough for asteroseismic analysis. Photometry was
collected at 1 minute cadence for >4 months from which we detected
19 distinct pulsation frequencies. Modeling the frequencies resulted in
precise knowledge of the fundamental stellar properties. Kepler-10 is
a relatively old (11.9 ± 4.5 Gyr) but otherwise Sun-like main-sequence
star with T <SUB>eff</SUB> = 5627 ± 44 K, M <SUB>sstarf</SUB> = 0.895
± 0.060 M <SUB>sun</SUB>, and R <SUB>sstarf</SUB> = 1.056 ± 0.021 R
<SUB>sun</SUB>. Physical models simultaneously fit to the transit light
curves and the precision Doppler measurements yielded tight constraints
on the properties of Kepler-10b that speak to its rocky composition: M
<SUB>P</SUB> = 4.56<SUP>+1.17</SUP> <SUB>-1.29</SUB> M <SUB>⊕</SUB>,
R <SUB>P</SUB> = 1.416<SUP>+0.033</SUP> <SUB>-0.036</SUB> R
<SUB>⊕</SUB>, and ρ<SUB>P</SUB> = 8.8<SUP>+2.1</SUP> <SUB>-2.9</SUB>
g cm<SUP>-3</SUP>. Kepler-10b is the smallest transiting exoplanet
discovered to date. <P />Based in part on observations obtained at
the W. M. Keck Observatory, which is operated by the University of
California and the California Institute of Technology.
---------------------------------------------------------
Title: Characteristics of Kepler Planetary Candidates Based on the
First Data Set
Authors: Borucki, William J.; Koch, David G.; Basri, Gibor;
Batalha, Natalie; Boss, Alan; Brown, Timothy M.; Caldwell, Douglas;
Christensen-Dalsgaard, Jørgen; Cochran, William D.; DeVore, Edna;
Dunham, Edward W.; Dupree, Andrea K.; Gautier, Thomas N., III;
Geary, John C.; Gilliland, Ronald; Gould, Alan; Howell, Steve B.;
Jenkins, Jon M.; Kjeldsen, Hans; Latham, David W.; Lissauer, Jack
J.; Marcy, Geoffrey W.; Monet, David G.; Sasselov, Dimitar; Tarter,
Jill; Charbonneau, David; Doyle, Laurance; Ford, Eric B.; Fortney,
Jonathan; Holman, Matthew J.; Seager, Sara; Steffen, Jason H.; Welsh,
William F.; Allen, Christopher; Bryson, Stephen T.; Buchhave, Lars;
Chandrasekaran, Hema; Christiansen, Jessie L.; Ciardi, David; Clarke,
Bruce D.; Dotson, Jessie L.; Endl, Michael; Fischer, Debra; Fressin,
Francois; Haas, Michael; Horch, Elliott; Howard, Andrew; Isaacson,
Howard; Kolodziejczak, Jeffery; Li, Jie; MacQueen, Phillip; Meibom,
Søren; Prsa, Andrej; Quintana, Elisa V.; Rowe, Jason; Sherry, William;
Tenenbaum, Peter; Torres, Guillermo; Twicken, Joseph D.; Van Cleve,
Jeffrey; Walkowicz, Lucianne; Wu, Hayley
2011ApJ...728..117B Altcode: 2010arXiv1006.2799B
In the spring of 2009, the Kepler Mission commenced high-precision
photometry on nearly 156,000 stars to determine the frequency and
characteristics of small exoplanets, conduct a guest observer program,
and obtain asteroseismic data on a wide variety of stars. On 2010
June 15, the Kepler Mission released most of the data from the first
quarter of observations. At the time of this data release, 705 stars
from this first data set have exoplanet candidates with sizes from as
small as that of Earth to larger than that of Jupiter. Here we give
the identity and characteristics of 305 released stars with planetary
candidates. Data for the remaining 400 stars with planetary candidates
will be released in 2011 February. More than half the candidates on
the released list have radii less than half that of Jupiter. Five
candidates are present in and near the habitable zone; two near
super-Earth size, and three bracketing the size of Jupiter. The
released stars also include five possible multi-planet systems. One
of these has two Neptune-size (2.3 and 2.5 Earth radius) candidates
with near-resonant periods.
---------------------------------------------------------
Title: Kepler photometry of the prototypical Blazhko star RR Lyr:
an old friend seen in a new light
Authors: Kolenberg, K.; Bryson, S.; Szabó, R.; Kurtz, D. W.; Smolec,
R.; Nemec, J. M.; Guggenberger, E.; Moskalik, P.; Benkő, J. M.;
Chadid, M.; Jeon, Y. -B.; Kiss, L. L.; Kopacki, G.; Nuspl, J.; Still,
M.; Christensen-Dalsgaard, J.; Kjeldsen, H.; Borucki, W. J.; Caldwell,
D. A.; Jenkins, J. M.; Koch, D.
2011MNRAS.411..878K Altcode: 2010arXiv1011.5908K
We present our analysis of the long-cadence Kepler data for the
well-studied Blazhko star RR Lyr, gathered during the first two
quarters of the satellite's observations and covering a total of 127
d. Besides being of great importance for our understanding of RR Lyrae
stars in general, these RR Lyr data can be regarded as a case study
for observations of bright stars with Kepler. Kepler can perform
high-precision photometry on targets like RR Lyr, as the saturated
flux is conserved to a very high degree. The Kepler data on RR Lyr are
revolutionary in several respects. Even with long-cadence sampling
(one measurement per 29.4 min), the unprecedented precision (<
mmag) of the Kepler photometry allows the study of the star's extreme
light-curve variations in detail. The multiplet structures at the main
frequency and its harmonics, typical for Blazhko stars, are clearly
detected up to the quintuplets. For the first time, photometric data
of RR Lyr reveal the presence of half-integer frequencies, linked to a
period-doubling effect. This phenomenon may be connected to the still
unexplained Blazhko modulation. Moreover, with three observed Blazhko
cycles at our disposal, we observe that there is no exact repetition in
the light-curve changes from one modulation cycle to the next for RR
Lyr. This may be due to additional periodicities in the star, or to
transient or quasi-periodic changes.
---------------------------------------------------------
Title: Atmospheric parameters and pulsational properties for a sample
of δ Sct, γ Dor and hybrid Kepler targets
Authors: Catanzaro, G.; Ripepi, V.; Bernabei, S.; Marconi, M.;
Balona, L.; Kurtz, D. W.; Smalley, B.; Borucki, W. J.; Bruntt, H.;
Christensen-Dalsgaard, J.; Grigahcène, A.; Kjeldsen, H.; Koch, D. G.;
Monteiro, M. J. P. F. G.; Suárez, J. C.; Szabó, R.; Uytterhoeven, K.
2011MNRAS.411.1167C Altcode: 2010arXiv1009.4317C; 2010MNRAS.tmp.1732C
We report spectroscopic observations for 19 δ Sct candidates observed
by the Kepler satellite both in long and short cadence mode. For all
these stars, by using spectral synthesis, we derive the effective
temperature, the surface gravity and the projected rotational
velocity. An equivalent spectral-type classification has been also
performed for all stars in the sample. These determinations are
fundamental for modelling the frequency spectra that will be extracted
from the Kepler data for asteroseismic inference. For all the 19 stars,
we also present periodograms obtained from Kepler data. We find that
all stars show peaks in both low- (γ Dor; g-mode) and high-frequency
(δ Sct; p-mode) regions. Using the amplitudes and considering 5 cycles
d<SUP>-1</SUP> as a boundary frequency, we classified three stars as
pure γ Dor, four as γ Dor-δ hybrid Sct, five as δ Sct-γ Dor hybrid
and six as pure δ Sct. The only exception is the star KIC 05296877,
which we suggest could be a binary. This work is based on spectra
taken at the Loiano (INAF - OA Bologna) and Serra La Nave (INAF -
OA Catania) Observatories.
---------------------------------------------------------
Title: The radius and mass of the close solar twin 18 Scorpii derived
from asteroseismology and interferometry
Authors: Bazot, M.; Ireland, M. J.; Huber, D.; Bedding, T. R.;
Broomhall, A. -M.; Campante, T. L.; Carfantan, H.; Chaplin, W. J.;
Elsworth, Y.; Meléndez, J.; Petit, P.; Théado, S.; Van Grootel,
V.; Arentoft, T.; Asplund, M.; Castro, M.; Christensen-Dalsgaard,
J.; Do Nascimento, J. D.; Dintrans, B.; Dumusque, X.; Kjeldsen, H.;
McAlister, H. A.; Metcalfe, T. S.; Monteiro, M. J. P. F. G.; Santos,
N. C.; Sousa, S.; Sturmann, J.; Sturmann, L.; ten Brummelaar, T. A.;
Turner, N.; Vauclair, S.
2011A&A...526L...4B Altcode: 2012arXiv1209.0217B
The growing interest in solar twins is motivated by the possibility of
comparing them directly to the Sun. To carry on this kind of analysis,
we need to know their physical characteristics with precision. Our
first objective is to use asteroseismology and interferometry on
the brightest of them: 18 Sco. We observed the star during 12 nights
with HARPS for seismology and used the PAVO beam-combiner at CHARA
for interferometry. An average large frequency separation 134.4 ±
0.3 μHz and angular and linear radiuses of 0.6759 ± 0.0062 mas and
1.010 ± 0.009 R<SUB>⊙</SUB> were estimated. We used these values
to derive the mass of the star, 1.02 ± 0.03 M<SUB>⊙</SUB>. <P
/>Based on observations collected at the European Southern Observatory
(ID 183.D-0729(A)) and at the CHARA Array, operated by Georgia State
University.
---------------------------------------------------------
Title: Kepler observations of the beaming binary KPD 1946+4340
Authors: Bloemen, S.; Marsh, T. R.; Østensen, R. H.; Charpinet,
S.; Fontaine, G.; Degroote, P.; Heber, U.; Kawaler, S. D.; Aerts,
C.; Green, E. M.; Telting, J.; Brassard, P.; Gänsicke, B. T.;
Handler, G.; Kurtz, D. W.; Silvotti, R.; Van Grootel, V.; Lindberg,
J. E.; Pursimo, T.; Wilson, P. A.; Gilliland, R. L.; Kjeldsen, H.;
Christensen-Dalsgaard, J.; Borucki, W. J.; Koch, D.; Jenkins, J. M.;
Klaus, T. C.
2011MNRAS.410.1787B Altcode: 2010arXiv1010.2747B; 2010MNRAS.tmp.1640B; 2010MNRAS.tmp.1742B
The Kepler Mission has acquired 33.5 d of continuous 1-min photometry
of KPD 1946+4340, a short-period binary system that consists of a
subdwarf B star (sdB) and a white dwarf. In the light curve, eclipses
are clearly seen, with the deepest occurring when the compact white
dwarf crosses the disc of the sdB (0.4 per cent) and the more shallow
ones (0.1 per cent) when the sdB eclipses the white dwarf. As expected,
the sdB is deformed by the gravitational field of the white dwarf, which
produces an ellipsoidal modulation of the light curve. Spectacularly,
a very strong Doppler beaming (also known as Doppler boosting) effect
is also clearly evident at the 0.1 per cent level. This originates
from the sdB's orbital velocity, which we measure to be 164.0 ± 1.9
km s<SUP>-1</SUP> from supporting spectroscopy. We present light-curve
models that account for all these effects, as well as gravitational
lensing, which decreases the apparent radius of the white dwarf by
about 6 per cent, when it eclipses the sdB. We derive system parameters
and uncertainties from the light curve using Markov chain Monte Carlo
simulations. Adopting a theoretical white dwarf mass-radius relation,
the mass of the subdwarf is found to be 0.47 ± 0.03 M<SUB>⊙</SUB>
and the mass of the white dwarf 0.59 ± 0.02 M<SUB>⊙</SUB>. The
effective temperature of the white dwarf is 15 900 ± 300 K. With
a spectroscopic effective temperature of T<SUB>eff</SUB>= 34 730 ±
250 K and a surface gravity of log g= 5.43 ± 0.04, the subdwarf has
most likely exhausted its core helium, and is in a shell He burning
stage. <P />The detection of Doppler beaming in Kepler light curves
potentially allows one to measure radial velocities without the
need of spectroscopic data. For the first time, a photometrically
observed Doppler beaming amplitude is compared to a spectroscopically
established value. The sdB's radial velocity amplitude derived from
the photometry (168 ± 4 km s<SUP>-1</SUP>) is in perfect agreement
with the spectroscopic value. After subtracting our best model for the
orbital effects, we searched the residuals for stellar oscillations
but did not find any significant pulsation frequencies.
---------------------------------------------------------
Title: Solar-like oscillations in red giants observed with Kepler:
comparison of global oscillation parameters from different methods
Authors: Hekker, S.; Elsworth, Y.; De Ridder, J.; Mosser, B.; García,
R. A.; Kallinger, T.; Mathur, S.; Huber, D.; Buzasi, D. L.; Preston,
H. L.; Hale, S. J.; Ballot, J.; Chaplin, W. J.; Régulo, C.; Bedding,
T. R.; Stello, D.; Borucki, W. J.; Koch, D. G.; Jenkins, J.; Allen,
C.; Gilliland, R. L.; Kjeldsen, H.; Christensen-Dalsgaard, J.
2011A&A...525A.131H Altcode: 2010arXiv1008.2959H
Context. The large number of stars for which uninterrupted
high-precision photometric timeseries data are being collected with
Kepler and CoRoT initiated the development of automated methods to
analyse the stochastically excited oscillations in main-sequence,
subgiant and red-giant stars. <BR /> Aims: We investigate the
differences in results for global oscillation parameters of G and K
red-giant stars due to different methods and definitions. We also
investigate uncertainties originating from the stochastic nature
of the oscillations. <BR /> Methods: For this investigation we use
Kepler data obtained during the first four months of operation. These
data have been analysed by different groups using already published
methods and the results are compared. We also performed simulations
to investigate the uncertainty on the resulting parameters due to
different realizations of the stochastic signal. <BR /> Results:
We obtain results for the frequency of maximum oscillation power
(ν_max) and the mean large separation (<Δν>) from different
methods for over one thousand red-giant stars. The results for these
parameters agree within a few percent and seem therefore robust to the
different analysis methods and definitions used here. The uncertainties
for ν_max and <Δν> due to differences in realization noise are
not negligible and should be taken into account when using these results
for stellar modelling. <P />Table 7 is only available in electronic
form at <A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: The Stellar Imager (SI) - A Mission to Resolve Stellar
Surfaces, Interiors, and Magnetic Activity
Authors: Christensen-Dalsgaard, Jørgen; Carpenter, Kenneth G.;
Schrijver, Carolus J.; Karovska, Margarita; Si Team
2011JPhCS.271a2085C Altcode:
The Stellar Imager (SI) is a space-based, UV/Optical Interferometer
(UVOI) designed to enable 0.1 milli-arcsecond (mas) spectral imaging
of stellar surfaces and of the Universe in general. It will also probe
via asteroseismology flows and structures in stellar interiors. SI
will enable the development and testing of a predictive dynamo model
for the Sun, by observing patterns of surface activity and imaging
of the structure and differential rotation of stellar interiors in
a population study of Sun-like stars to determine the dependence of
dynamo action on mass, internal structure and flows, and time. SI's
science focuses on the role of magnetism in the Universe and will
revolutionize our understanding of the formation of planetary systems,
of the habitability and climatology of distant planets, and of many
magneto-hydrodynamically controlled processes in the Universe. SI
is a "Landmark/Discovery Mission" in the 2005 Heliophysics Roadmap,
an implementation of the UVOI in the 2006 Astrophysics Strategic Plan,
and a NASA Vision Mission ("NASA Space Science Vision Missions" (2008),
ed. M. Allen). We present here the science goals of the SI Mission,
a mission architecture that could meet those goals, and the technology
development needed to enable this mission. Additional information on
SI can be found at: http://hires.gsfc.nasa.gov/si/.
---------------------------------------------------------
Title: Asteroseismology of the Transiting Exoplanet Host HD 17156
with Hubble Space Telescope Fine Guidance Sensor
Authors: Gilliland, Ronald L.; McCullough, Peter R.; Nelan,
Edmund P.; Brown, Timothy M.; Charbonneau, David; Nutzman, Philip;
Christensen-Dalsgaard, Jørgen; Kjeldsen, Hans
2011ApJ...726....2G Altcode: 2010arXiv1011.0435G
Observations conducted with the Fine Guidance Sensor on the Hubble
Space Telescope (HST) providing high cadence and precision time-series
photometry were obtained over 10 consecutive days in 2008 December on
the host star of the transiting exoplanet HD 17156b. During this time,
1.0 × 10<SUP>12</SUP> photons (corrected for detector dead time) were
collected in which a noise level of 163 parts per million per 30 s sum
resulted, thus providing excellent sensitivity to the detection of the
analog of the solar 5-minute p-mode oscillations. For HD 17156, robust
detection of p modes supports the determination of the stellar mean
density of langρ<SUB>*</SUB>rang = 0.5301 ± 0.0044 g cm<SUP>-3</SUP>
from a detailed fit to the observed frequencies of modes of degree l =
0, 1, and 2. This is the first star for which the direct determination
of langρ<SUB>*</SUB>rang has been possible using both asteroseismology
and detailed analysis of a transiting planet light curve. Using
the density constraint from asteroseismology, and stellar evolution
modeling results in M <SUB>*</SUB> = 1.285 ± 0.026 M <SUB>sun</SUB>,
R <SUB>*</SUB> = 1.507 ± 0.012 R <SUB>sun</SUB>, and a stellar age of
3.2 ± 0.3 Gyr. <P />Based on observations with the NASA/ESA Hubble
Space Telescope, obtained at the Space Telescope Science Institute,
which is operated by AURA, Inc., under NASA contract NAS 5-26555.
---------------------------------------------------------
Title: Precise Estimates of the Physical Parameters for the Exoplanet
System HD 17156 Enabled by Hubble Space Telescope Fine Guidance
Sensor Transit and Asteroseismic Observations
Authors: Nutzman, Philip; Gilliland, Ronald L.; McCullough, Peter R.;
Charbonneau, David; Christensen-Dalsgaard, Jørgen; Kjeldsen, Hans;
Nelan, Edmund P.; Brown, Timothy M.; Holman, Matthew J.
2011ApJ...726....3N Altcode: 2010arXiv1011.0440N
We present observations of three distinct transits of HD 17156b
obtained with the Fine Guidance Sensors on board the Hubble Space
Telescope. We analyzed both the transit photometry and previously
published radial velocities to find the planet-star radius ratio
R<SUB>p</SUB> /R <SUB>sstarf</SUB> = 0.07454 ± 0.00035, inclination i =
86.49<SUP>+0.24</SUP> <SUB>-0.20</SUB> deg, and scaled semimajor axis
a/R <SUB>sstarf</SUB> = 23.19<SUP>+0.32</SUP> <SUB>-0.27</SUB>. This
last value translates directly to a mean stellar density determination
ρ<SUB>sstarf</SUB> = 0.522<SUP>+0.021</SUP> <SUB>-0.018</SUB>
g cm<SUP>-3</SUP>. Analysis of asteroseismology observations by
the companion paper of Gilliland et al. provides a consistent but
significantly refined measurement of ρ<SUB>sstarf</SUB> = 0.5308 ±
0.0040. We compare stellar isochrones to this density estimate and find
M <SUB>sstarf</SUB> = 1.275 ± 0.018 M <SUB>sun</SUB> and a stellar
age of 3.37<SUP>+0.20</SUP> <SUB>-0.47</SUB> Gyr. Using this estimate
of M <SUB>sstarf</SUB> and incorporating the density constraint from
asteroseismology, we model both the photometry and published radial
velocities to estimate the planet radius R<SUB>p</SUB> = 1.0870 ±
0.0066 R<SUB>J</SUB> and the stellar radius R <SUB>sstarf</SUB> =
1.5007 ± 0.0076 R <SUB>sun</SUB>. The planet radius is larger than
that found in previous studies and consistent with theoretical models
of a solar-composition gas giant of the same mass and equilibrium
temperature. For the three transits, we determine the times of
mid-transit to a precision of 6.2 s, 7.6 s, and 6.9 s, and the
transit times for HD 17156 do not show any significant departures
from a constant period. The joint analysis of transit photometry and
asteroseismology presages similar studies that will be enabled by the
NASA Kepler Mission. <P />Based on observations with the NASA/ESA Hubble
Space Telescope obtained at the Space Telescope Science Institute,
which is operated by the Association of Universities for Research in
Astronomy, Incorporated, under NASA contract NAS5-26555.
---------------------------------------------------------
Title: Kepler observations of rapidly oscillating Ap, δ Scuti and
γ Doradus pulsations in Ap stars
Authors: Balona, L. A.; Cunha, M. S.; Kurtz, D. W.; Brandão, I. M.;
Gruberbauer, M.; Saio, H.; Östensen, R.; Elkin, V. G.; Borucki, W. J.;
Christensen-Dalsgaard, J.; Kjeldsen, H.; Koch, D. G.; Bryson, S. T.
2011MNRAS.410..517B Altcode: 2010arXiv1006.4013B; 2010MNRAS.tmp.1549B
Observations of the A5p star KIC 8677585 obtained during the Kepler
10-d commissioning run with 1-min time resolution show that it is a
rapidly oscillating Ap (roAp) star with several frequencies with periods
near 10 min. In addition, a low frequency at 3.142 d<SUP>-1</SUP> is
also clearly present. Multiperiodic γ Doradus (γ Dor) and δ Scuti
(δ Sct) pulsations, never before seen in any Ap star, are present
in Kepler observations of at least three other Ap stars. Since γ Dor
pulsations are seen in Ap stars, it is likely that the low frequency
in KIC 8677585 is also a γ Dor pulsation. The simultaneous presence
of both γ Dor and roAp pulsations and the unexpected detection of δ
Sct and γ Dor pulsations in Ap stars present new opportunities and
challenges for the interpretation of these stars. Since it is easy to
confuse Am and Ap stars at classification dispersions, the nature of
these Ap stars in the Kepler field needs to be confirmed.
---------------------------------------------------------
Title: First Global Rotation Inversions of HMI Data
Authors: Howe, R.; Larson, T. P.; Schou, J.; Hill, F.; Komm, R.;
Christensen-Dalsgaard, J.; Thompson, M. J.
2011JPhCS.271a2061H Altcode:
We present the first 2-dimensional global rotational inversions of
medium-degree p-mode data from the Helioseismic and Magnetic Imager,
and compare the results with inversions of Michelson Doppler Imager
data for the same time period. The inferred rotation profiles show
good agreement between the two instruments.
---------------------------------------------------------
Title: Discovery of a New AM CVn System with the Kepler Satellite
Authors: Fontaine, G.; Brassard, P.; Green, E. M.; Charpinet, S.;
Dufour, P.; Hubeny, I.; Steeghs, D.; Aerts, C.; Randall, S. K.;
Bergeron, P.; Guvenen, B.; O'Malley, C. J.; Van Grootel, V.; Østensen,
R. H.; Bloemen, S.; Silvotti, R.; Howell, S. B.; Baran, A.; Kepler,
S. O.; Marsh, T. R.; Montgomery, M. H.; Oreiro, R.; Provencal, J.;
Telting, J.; Winget, D. E.; Zima, W.; Christensen-Dalsgaard, J.;
Kjeldsen, H.
2011ApJ...726...92F Altcode:
We report the discovery of a new AM CVn system on the basis of
broadband photometry obtained with the Kepler satellite supplemented
by ground-based optical spectroscopy. Initially retained on Kepler
target lists as a potential compact pulsator, the blue object SDSS
J190817.07+394036.4 (KIC 004547333) has turned out to be a high-state
AM CVn star showing the He-dominated spectrum of its accretion disk
significantly reddened by interstellar absorption. We constructed
new grids of NLTE synthetic spectra for accretion disks in order to
analyze our spectroscopic observations. From this analysis, we infer
preliminary estimates of the rate of mass transfer, the inclination
angle of the disk, and the distance to the system. The AM CVn nature
of the system is also evident in the Kepler light curve, from which
we extracted 11 secure periodicities. The luminosity variations are
dominated by a basic periodicity of 938.507 s, likely to correspond to a
superhump modulation. The light curve folded on the period of 938.507 s
exhibits a pulse shape that is very similar to the superhump wavefront
seen in AM CVn itself, which is a high-state system and the prototype
of the class. Our Fourier analysis also suggests the likely presence
of a quasi-periodic oscillation similar to those already observed in
some high-state AM CVn systems. Furthermore, some very low-frequency,
low-amplitude aperiodic photometric activity is likely present, which
is in line with what is expected in accreting binary systems. Inspired
by previous work, we further looked for and found some intriguing
numerical relationships between the 11 secure detected frequencies,
in the sense that we can account for all of them in terms of only
three basic clocks. This is further evidence in favor of the AM CVn
nature of the system.
---------------------------------------------------------
Title: SONG - getting ready for the prototype
Authors: Grundahl, F.; Christensen-Dalsgaard, J.; Gråe Jørgensen,
U.; Frandsen, S.; Kjeldsen, H.; Kjærgaard Rasmussen, P.
2011JPhCS.271a2083G Altcode:
The Stellar Observations Network Group, SONG, is a project which
aims at building a network of eight identical telescopes distributed
geographically around the globe to allow long-term, high-duty-cycle
observations of stellar oscillations and to search for exoplanets
via the microlensing technique. At each of the network nodes a 1 m
telescope with a high-resolution spectrograph and two lucky-imaging
cameras is placed. The instruments and telescope, for the prototype
node, are currently being built and installation at Observatorio del
Teide, Tenerife, Spain is foreseen for early 2011.
---------------------------------------------------------
Title: The torsional oscillation and the new solar cycle
Authors: Howe, R.; Hill, F.; Komm, R.; Christensen-Dalsgaard, J.;
Larson, T. P.; Schou, J.; Thompson, M. J.; Ulrich, R.
2011JPhCS.271a2074H Altcode:
We present updated observations of the pattern of migrating solar
zonal flows known as the torsional oscillation, covering 15 years of
helioseismic measurements with GONG and MDI and 30 years of surface
Doppler observations from Mount Wilson. We compare the behavior of the
flows during the extended solar minimum following Cycle 23 with that in
earlier minima. We demonstrate that the timing of the migration of the
zonal flow belts may be of some use in predicting the start of the new
cycle. We also note that the behavior of the high-latitude part of the
pattern currently differs from that seen early in the previous cycle,
with the high-latitude poleward-migrating branch still not established.
---------------------------------------------------------
Title: Rotation-rate variations at the tachocline: An update
Authors: Howe, R.; Komm, R.; Hill, F.; Christensen-Dalsgaard, J.;
Larson, T. P.; Schou, J.; Thompson, M. J.; Toomre, J.
2011JPhCS.271a2075H Altcode:
After 15 years of GONG and MDI observations of the solar interior
rotation, we revisit the issue of variations in the rotation rate near
the base of the convection zone. The 1.3-year period seen in the first
few years of the observations disappeared after 2000 and has still
not returned. On the other hand, the agreement between GONG and MDI
observations suggests that variations seen in this region have some
solar origin, whether a true rotation-rate change or possibly mere
stochastic variation; we present a numerical experiment supporting
this contention.
---------------------------------------------------------
Title: Seismic signatures of stellar cores of solar-like pulsators:
Dependence on mass and age
Authors: Brandão, I. M.; Cunha, M. S.; Creevey, O. L.;
Christensen-Dalsgaard, J.
2010AN....331..940B Altcode: 2010arXiv1008.2630B
Useful information from the inner layers of stellar pulsators may be
derived from the study of their oscillations. In this paper we analyse
three diagnostic tools suggested in the literature built from the
oscillation frequencies computed for a set of main sequence models
with masses between 1.0 M<SUB>⊙</SUB> and 1.6 M<SUB>⊙</SUB>,
to check what information they may hold about stellar cores. For the
models with convective cores ({M ≥ 1.2} M<SUB>⊙</SUB>) we find
a relation between the frequency slopes of the diagnostic tools and
the size of the jump in the sound speed at the edge of the core. We
show that this relation is independent of the mass of the models. In
practice, since the size of the jump in the sound speed is related to
the age of the star, using these seismic tools we may, in principle,
infer the star's evolutionary state. We also show that when combining
two of the three diagnostic tools studied, we are able to distinguish
models with convective cores from models without a convective core
but with strong sound speed gradients in the inner layers
---------------------------------------------------------
Title: Kepler observations: Light shed on the hybrid γ Doradus -
δ Scuti pulsation phenomenon
Authors: Grigahcène, A.; Uytterhoeven, K.; Antoci, V.; Balona, L.;
Catanzaro, G.; Daszyńska-Daszkiewicz, J.; Guzik, J. A.; Handler, G.;
Houdek, G.; Kurtz, D. W.; Marconi, M.; Monteiro, M. J. P. F. G.;
Moya, A.; Ripepi, V.; Suárez, J. -C.; Borucki, W. J.; Brown,
T. M.; Christensen-Dalsgaard, J.; Gilliland, R. L.; Jenkins, J. M.;
Kjeldsen, H.; Koch, D.; Bernabei, S.; Bradley, P.; Breger, M.; Di
Criscienzo, M.; Dupret, M. -A.; García, R. A.; García Hernández, A.;
Jackiewicz, J.; Kaiser, A.; Lehmann, H.; Martín-Ruiz, S.; Mathias,
P.; Molenda-Żakowicz, J.; Nemec, J. M.; Nuspl, J.; Paparó, M.;
Roth, M.; Szabó, R.; Suran, M. D.; Ventura, R.
2010AN....331..989G Altcode:
Through the observational study of stellar pulsations, the internal
structure of stars can be probed and theoretical models can be
tested. The main sequence γ Doradus (Dor) and δ Scuti (Sct) stars
with masses 1.2-2.5 M<SUB>⊙</SUB> are particularly interesting for
asteroseismic study. The γ Dor stars pulsate in high-order gravity (g)
modes, with pulsational periods of order of one day. The δ Sct stars,
on the other hand, show low-order g and pressure (p) modes with periods
of order of 2 hours. Theory predicts the existence of `hybrid' stars,
i.e. stars pulsating in both types of modes, in an overlap region
between the instability strips of γ Dor and δ Sct stars in the
Hertzsprung-Russell diagram. Hybrid stars are particularly interesting
as the two types of modes probe different regions of the stellar
interior and hence provide complementary model constraints. Before
the advent of Kepler, only a few hybrid stars had been confirmed. The
{{Kepler}} satellite is providing a true revolution in the study
of and search for hybrid stars. Analysis of the first 50 days of
{{Kepler}} data of hundreds of γ Dor and δ Sct candidates reveals
extremely rich frequency spectra, with most stars showing frequencies
in both the δ Sct and γ Dor frequency range. As these results show
that there are practically no pure δ Sct or γ Dor pulsators, a new
observational classification scheme is proposed by \cite{Grig10}. We
present their results and characterize 234 stars in terms of δ Sct,
γ Dor, δ Sct/γ Dor or γ Dor/δ Sct hybrids.
---------------------------------------------------------
Title: The Kepler Asteroseismic Investigation: Scientific goals and
first results
Authors: Kjeldsen, H.; Christensen-Dalsgaard, J.; Handberg, R.; Brown,
T. M.; Gilliland, R. L.; Borucki, W. J.; Koch, D.
2010AN....331..966K Altcode: 2010arXiv1007.1816K
Kepler is a NASA mission designed to detect exoplanets and characterize
the properties of exoplanetary systems. Kepler also includes an
asteroseismic programme which is being conducted through the Kepler
Asteroseismic Science Consortium (KASC), whose 400 members are organized
into 13 working groups by type of variable star. So far data have been
available from the first 7 month of the mission containing a total of
2937 targets observed at a 1-min cadence for periods between 10 days and
7 months. The goals of the asteroseismic part of the Kepler project is
to perform detailed studies of stellar interiors. The first results of
the asteroseismic analysis are orders of magnitude better than seen
before, and this bodes well for how the future analysis of Kepler
data for many types of stars will impact our general understanding of
stellar structure and evolution.
---------------------------------------------------------
Title: Does Kepler unveil the mystery of the Blazhko effect? First
detection of period doubling in Kepler Blazhko RR Lyrae stars
Authors: Szabó, R.; Kolláth, Z.; Molnár, L.; Kolenberg, K.; Kurtz,
D. W.; Bryson, S. T.; Benkő, J. M.; Christensen-Dalsgaard, J.;
Kjeldsen, H.; Borucki, W. J.; Koch, D.; Twicken, J. D.; Chadid, M.;
di Criscienzo, M.; Jeon, Y. -B.; Moskalik, P.; Nemec, J. M.; Nuspl, J.
2010MNRAS.409.1244S Altcode: 2010MNRAS.tmp.1401S; 2010arXiv1007.3404S
The first detection of the period doubling phenomenon is reported in
the Kepler RR Lyrae stars RR Lyr, V808 Cyg and V355 Lyr. Interestingly,
all these pulsating stars show Blazhko modulation. The period doubling
manifests itself as alternating maxima and minima of the pulsational
cycles in the light curve, as well as through the appearance of
half-integer frequencies located halfway between the main pulsation
period and its harmonics in the frequency spectrum. The effect
was found to be stronger during certain phases of the modulation
cycle. We were able to reproduce the period-doubling bifurcation
in our non-linear RR Lyrae models computed by the Florida-Budapest
hydrocode. This enabled us to trace the origin of this instability
in RR Lyrae stars to a resonance, namely a 9:2 resonance between the
fundamental mode and a high-order (ninth) radial overtone showing
strange-mode characteristics. We discuss the connection of this new
type of variation to the mysterious Blazhko effect and argue that it
may give us fresh insights into solving this century-old enigma.
---------------------------------------------------------
Title: Flavours of variability: 29 RR Lyrae stars observed with Kepler
Authors: Benkő, J. M.; Kolenberg, K.; Szabó, R.; Kurtz, D. W.;
Bryson, S.; Bregman, J.; Still, M.; Smolec, R.; Nuspl, J.; Nemec,
J. M.; Moskalik, P.; Kopacki, G.; Kolláth, Z.; Guggenberger, E.;
di Criscienzo, M.; Christensen-Dalsgaard, J.; Kjeldsen, H.; Borucki,
W. J.; Koch, D.; Jenkins, J. M.; van Cleve, J. E.
2010MNRAS.409.1585B Altcode: 2010arXiv1007.3928B; 2010MNRAS.tmp.1514B
We present our analysis of Kepler observations of 29 RR Lyrae stars,
based on 138 d of observation. We report precise pulsation periods
for all stars. Nine of these stars had incorrect or unknown periods
in the literature. 14 of the stars exhibit both amplitude and phase
Blazhko modulations, with Blazhko periods ranging from 27.7 to more
than 200 d. For V445 Lyr, a longer secondary variation is also observed
in addition to its 53.2-d Blazhko period. The unprecedented precision
of the Kepler photometry has led to the discovery of the the smallest
modulations detected so far. Moreover, additional frequencies beyond
the well-known harmonics and Blazhko multiplets have been found. These
frequencies are located around the half-integer multiples of the
main pulsation frequency for at least three stars. In four stars,
these frequencies are close to the first and/or second overtone
modes. The amplitudes of these periodicities seem to vary over the
Blazhko cycle. V350 Lyr, a non-Blazhko star in our sample, is the
first example of a double-mode RR Lyrae star that pulsates in its
fundamental and second overtone modes.
---------------------------------------------------------
Title: First Kepler results on compact pulsators - III. Subdwarf B
stars with V1093 Her and hybrid (DW Lyn) type pulsations
Authors: Reed, M. D.; Kawaler, S. D.; Østensen, R. H.; Bloemen, S.;
Baran, A.; Telting, J. H.; Silvotti, R.; Charpinet, S.; Quint, A. C.;
Handler, G.; Gilliland, R. L.; Borucki, W. J.; Koch, D. G.; Kjeldsen,
H.; Christensen-Dalsgaard, J.
2010MNRAS.409.1496R Altcode: 2010arXiv1008.0582R; 2010MNRAS.tmp.1698R
We present the discovery of non-radial pulsations in five hot subdwarf B
(sdB) stars based on 27 d of nearly continuous time series photometry
using the Kepler spacecraft. We find that every sdB star cooler than
≈27 500 K that Kepler has observed (seven so far) is a long-period
pulsator of the V1093 Her (PG 1716) class or a hybrid star with both
short and long periods. The apparently non-binary long-period and
hybrid pulsators are described here. The V1093 Her periods range from
1 to 4.5 h and are associated with g-mode pulsations. Three stars also
exhibit short periods indicative of p-modes with periods of 2-5 min and
in addition, these stars exhibit periodicities between both classes
from 15 to 45 min. We detect the coolest and longest-period V1093
Her-type pulsator to date, KIC010670103 (T<SUB>eff</SUB>≈ 20 900 K,
P<SUB>max</SUB>≈ 4.5 h) as well as a suspected hybrid pulsator,
KIC002697388, which is extremely cool (T<SUB>eff</SUB>≈ 23 900
K) and for the first time hybrid pulsators which have larger g-mode
amplitudes than p-mode ones. All of these pulsators are quite rich with
many frequencies and we are able to apply asymptotic relationships
to associate periodicities with modes for KIC010670103. Kepler data
are particularly well suited for these studies as they are long
duration, extremely high duty cycle observations with well-behaved
noise properties.
---------------------------------------------------------
Title: First Kepler results on compact pulsators - I. Survey target
selection and the first pulsators
Authors: Østensen, R. H.; Silvotti, R.; Charpinet, S.; Oreiro, R.;
Handler, G.; Green, E. M.; Bloemen, S.; Heber, U.; Gänsicke, B. T.;
Marsh, T. R.; Kurtz, D. W.; Telting, J. H.; Reed, M. D.; Kawaler,
S. D.; Aerts, C.; Rodríguez-López, C.; Vučković, M.; Ottosen,
T. A.; Liimets, T.; Quint, A. C.; Van Grootel, V.; Randall, S. K.;
Gilliland, R. L.; Kjeldsen, H.; Christensen-Dalsgaard, J.; Borucki,
W. J.; Koch, D.; Quintana, E. V.
2010MNRAS.409.1470O Altcode: 2010MNRAS.409.1470A; 2010arXiv1007.3170O; 2010MNRAS.tmp.1696O
We present results from the first two quarters of a survey to search for
pulsations in compact stellar objects with the Kepler spacecraft. The
survey sample and the various methods applied in its compilation are
described, and spectroscopic observations are presented to separate the
objects into accurate classes. From the Kepler photometry we clearly
identify nine compact pulsators and a number of interesting binary
stars. Of the pulsators, one shows the strong, rapid pulsations typical
of a V361 Hya-type sdB variable (sdBV); seven show long-period pulsation
characteristics of V1093 Her-type sdBVs; and one shows low-amplitude
pulsations with both short and long periods. We derive effective
temperatures and surface gravities for all the subdwarf B stars in
the sample and demonstrate that below the boundary region where hybrid
sdB pulsators are found, all our targets are pulsating. For the stars
hotter than this boundary temperature a low fraction of strong pulsators
(<10 per cent) is confirmed. Interestingly, the short-period pulsator
also shows a low-amplitude mode in the long-period region, and several
of the V1093 Her pulsators show low-amplitude modes in the short-period
region, indicating that hybrid behaviour may be common in these stars,
also outside the boundary temperature region where hybrid pulsators
have hitherto been found.
---------------------------------------------------------
Title: Asteroseismic modelling of Procyon A: Preliminary results
Authors: Doğan, G.; Bonanno, A.; Bedding, T. R.; Campante, T. L.;
Christensen-Dalsgaard, J.; Kjeldsen, H.
2010AN....331..949D Altcode: 2010arXiv1006.5912D
We present our preliminary results of the modelling of the F5 star
Procyon A. The frequencies predicted by our models are compared with
the frequencies extracted through a global fit to the power spectrum
obtained by the latest ground-based observations, which provides two
different mode identification scenarios.
---------------------------------------------------------
Title: Asteroseismology of solar-type stars with Kepler I: Data
analysis
Authors: Karoff, C.; Chaplin, W. J.; Appourchaux, T.; Elsworth, Y.;
Garcia, R. A.; Houdek, G.; Metcalfe, T. S.; Molenda-Żakowicz, J.;
Monteiro, M. J. P. F. G.; Thompson, M. J.; Christensen-Dalsgaard, J.;
Gilliland, R. L.; Kjeldsen, H.; Basu, S.; Bedding, T. R.; Campante,
T. L.; Eggenberger, P.; Fletcher, S. T.; Gaulme, P.; Handberg, R.;
Hekker, S.; Martic, M.; Mathur, S.; Mosser, B.; Regulo, C.; Roxburgh,
I. W.; Salabert, D.; Stello, D.; Verner, G. A.; Belkacem, K.; Biazzo,
K.; Cunha, M. S.; Gruberbauer, M.; Guzik, J. A.; Kupka, F.; Leroy,
B.; Ludwig, H. -G.; Mathis, S.; Noels, A.; Noyes, R. W.; Roca Cortes,
T.; Roth, M.; Sato, K. H.; Schmitt, J.; Suran, M. D.; Trampedach,
R.; Uytterhoeven, K.; Ventura, R.
2010AN....331..972K Altcode: 2010arXiv1005.0507K
We report on the first asteroseismic analysis of solar-type stars
observed by Kepler. Observations of three G-type stars, made at
one-minute cadence during the first 33.5 days of science operations,
reveal high signal-to-noise solar-like oscillation spectra in all three
stars: About 20 modes of oscillation can clearly be distinguished
in each star. We discuss the appearance of the oscillation spectra,
including the presence of a possible signature of faculae, and the
presence of mixed modes in one of the three stars.
---------------------------------------------------------
Title: Four years of HELAS
Authors: Roth, M.; Lühe, O. v. d.; Aerts, C.; Christensen-Dalsgaard,
J.; Corbard, T.; Daszyńska-Daszkiewicz, J.; Di Mauro, M. P.; Gizon,
L.; Jiménez-Reyes, S.; Monteiro, M. J. P. F. G.; Pallé, P. L.;
Thompson, M. J.
2010AN....331.1084R Altcode:
The European Coordination Action on HELio- and ASteroseismology
(HELAS) has completed its fourth and final year of initial funding by
the European Commission. Set up as a network which combines solar and
stellar physics communities in the important and vigorously evolving
field of seismology, HELAS has been able to coordinate the efforts of
European astronomers with remarkable success. Four large international
conferences including the HELAS-IV conference on Lanzarote as well as
many workshops were organized with a substantial contribution from
HELAS. About a dozen workshops, addressing specialized questions in
global and local helioseismology and asteroseismology were entirely
organized by HELAS. Data analysis tools to prepare the European
communities for the upcoming influx of data from new missions have
been prepared, tested and demonstrated. Lecture notes and outreach
material have been assembled and prepared for general access. As a
result, HELAS has an important impact on the scientific output of the
astrophysics seismology communities and significantly increased the
visibility of European research in this field. This paper summarizes
the activities and accomplishments of HELAS.
---------------------------------------------------------
Title: First Kepler results on compact pulsators - V. Slowly pulsating
subdwarf B stars in short-period binaries
Authors: Kawaler, S. D.; Reed, M. D.; Østensen, R. H.; Bloemen,
S.; Kurtz, D. W.; Quint, A. C.; Silvotti, R.; Baran, A. S.; Green,
E. M.; Charpinet, S.; Telting, J.; Aerts, C.; Handler, G.; Kjeldsen,
H.; Christensen-Dalsgaard, J.; Borucki, W. J.; Koch, D. G.
2010MNRAS.409.1509K Altcode: 2010MNRAS.tmp.1700K; 2010arXiv1008.0553K
The survey phase of the Kepler Mission includes a number of hot
subdwarf B (sdB) stars to search for non-radial pulsations. We present
our analysis of two sdB stars that are found to be g-mode pulsators
of the V1093 Her class. These two stars also display the distinct
irradiation effect typical of sdB stars with a close M-dwarf companion
with orbital periods of less than half a day. Because the orbital period
is so short, the stars should be in synchronous rotation, and if so, the
rotation period should imprint itself on the multiplet structure of the
pulsations. However, we do not find clear evidence for such rotational
splitting. Though the stars do show some frequency spacings that are
consistent with synchronous rotation, they also display multiplets
with splittings that are much smaller. Longer-duration time series
photometry will be needed to determine if those small splittings are
in fact rotational splitting, or caused by slow amplitude or phase
modulation. Further data should also improve the signal-to-noise ratio,
perhaps revealing lower-amplitude periodicities that could confirm
the expectation of synchronous rotation. The pulsation periods seen in
these stars show period spacings that are suggestive of high-overtone
g-mode pulsations.
---------------------------------------------------------
Title: First Kepler results on compact pulsators - II. KIC 010139564,
a new pulsating subdwarf B (V361 Hya) star with an additional
low-frequency mode
Authors: Kawaler, S. D.; Reed, M. D.; Quint, A. C.; Østensen, R. H.;
Silvotti, R.; Baran, A. S.; Charpinet, S.; Bloemen, S.; Kurtz, D. W.;
Telting, J.; Handler, G.; Kjeldsen, H.; Christensen-Dalsgaard, J.;
Borucki, W. J.; Koch, D. G.
2010MNRAS.409.1487K Altcode: 2010arXiv1008.2356K; 2010MNRAS.tmp.1701K
We present the discovery of non-radial pulsations in a hot subdwarf B
star based on 30.5 d of nearly continuous time series photometry using
the Kepler spacecraft. KIC 010139564 is found to be a short-period
pulsator of the V361 Hya (EC 14026) class with more than 10 independent
pulsation modes whose periods range from 130 to 190 s. It also shows one
periodicity at a period of 3165 s. If this periodicity is a high-order
g-mode, then this star may be the hottest member of the hybrid DW Lyn
stars. In addition to the resolved pulsation frequencies, additional
periodic variations in the light curve suggest that a significant
number of additional pulsation frequencies may be present. The long
duration of the run, the extremely high duty cycle and the well-behaved
noise properties allow us to explore the stability of the periodic
variations, and to place strong constraints on how many of them
are independent stellar oscillation modes. We find that most of the
identified periodicities are indeed stable in phase and amplitude,
suggesting a rotation period of 2-3 weeks for this star, but further
observations are needed to confirm this suspicion.
---------------------------------------------------------
Title: Automatic Determination of Stellar Parameters Via
Asteroseismology of Stochastically Oscillating Stars: Comparison
with Direct Measurements
Authors: Quirion, Pierre-Olivier; Christensen-Dalsgaard, Jørgen;
Arentoft, Torben
2010ApJ...725.2176Q Altcode: 2010arXiv1009.5131Q
Space-based projects are providing a wealth of high-quality
asteroseismic data, including frequencies for a large number of stars
showing solar-like oscillations. These data open the prospect for
precise determinations of key stellar parameters, of particular value to
the study of extra-solar planetary systems. Given the quantity of the
available and expected data, it is important to develop efficient and
reliable techniques for analyzing them, including the determination of
stellar parameters from the observed frequencies. Here we present the
SEEK package developed for the analysis of asteroseismic data from the
Kepler mission. A central goal of the package is to obtain a fast and
automatic determination of the stellar radius and other parameters in
a form that is statistically well defined. The algorithms are tested
by comparing the results of the analysis with independent measurements
of stellar radius and mass for a sample of well-observed stars. We
conclude that the SEEK package fixes stellar parameters with accuracy
and precision.
---------------------------------------------------------
Title: Seismological challenges for stellar structure
Authors: Christensen-Dalsgaard, J.
2010AN....331..866C Altcode: 2010arXiv1007.1720C
Helioseismology has provided very detailed information about the solar
interior, and extensive data on a large number of stars, although at
less detail, are promised by the ongoing and upcoming asteroseismic
projects. In the solar case there remain serious challenges in
understanding the inferred solar structure, particularly in the light
of the revised determinations of the solar surface composition. Also,
a secure understanding of the origins of solar rotation as inferred from
helioseismology, both in the radiative interior and in the convection
zone, is still missing. In the stellar case challenges are certain to
appear as the data allow more detailed inferences of the properties
of stellar cores. Large remaining uncertainties in modelling concern
the properties of convective cores and other processes that may cause
mixing. As a result of developing asteroseismic signatures addressing
these and other issues, we can look forward to a highly challenging,
and hence exciting, era of stellar astrophysics.
---------------------------------------------------------
Title: Solar-like oscillations in cluster stars
Authors: Stello, D.; Basu, S.; Bedding, T. R.; Brogaard, K.; Bruntt,
H.; Chaplin, W. J.; Christensen-Dalsgaard, J.; Demarque, P.; Elsworth,
Y. P.; García, R. A.; Gilliland, R. L.; Hekker, S.; Huber, D.;
Karoff, C.; Kjeldsen, H.; Lebreton, Y.; Mathur, S.; Meibom, S.;
Molenda-Żakowicz, J.; Noels, A.; Roxburgh, I. W.; Silva Aguirre,
V.; Sterken, C.; Szabó, R.
2010AN....331..985S Altcode: 2010arXiv1007.0009S
This article summaries a talk given at the HELAS IV international
meeting We present a brief overview of the history of attempts to
obtain a clear detection of solar-like oscillations in cluster stars,
and discuss the results on the first clear detection, which was made
by the Kepler Asteroseismic Science Consortium (KASC) Working Group
2. <P />Data from Kepler.
---------------------------------------------------------
Title: Asteroseismology of Red Giants from the First Four Months of
Kepler Data: Global Oscillation Parameters for 800 Stars
Authors: Huber, D.; Bedding, T. R.; Stello, D.; Mosser, B.; Mathur,
S.; Kallinger, T.; Hekker, S.; Elsworth, Y. P.; Buzasi, D. L.; De
Ridder, J.; Gilliland, R. L.; Kjeldsen, H.; Chaplin, W. J.; García,
R. A.; Hale, S. J.; Preston, H. L.; White, T. R.; Borucki, W. J.;
Christensen-Dalsgaard, J.; Clarke, B. D.; Jenkins, J. M.; Koch, D.
2010ApJ...723.1607H Altcode: 2010arXiv1010.4566H
We have studied solar-like oscillations in ~800 red giant stars
using Kepler long-cadence photometry. The sample includes stars
ranging in evolution from the lower part of the red giant branch to
the helium main sequence. We investigate the relation between the
large frequency separation (Δν) and the frequency of maximum power
(ν<SUB>max</SUB>) and show that it is different for red giants than
for main-sequence stars, which is consistent with evolutionary models
and scaling relations. The distributions of ν<SUB>max</SUB> and Δν
are in qualitative agreement with a simple stellar population model
of the Kepler field, including the first evidence for a secondary
clump population characterized by M >~ 2 M <SUB>sun</SUB> and
ν<SUB>max</SUB> ~= 40-110 μHz. We measured the small frequency
separations δν<SUB>02</SUB> and δν<SUB>01</SUB> in over 400
stars and δν<SUB>03</SUB> in over 40. We present C-D diagrams
for l = 1, 2, and 3 and show that the frequency separation ratios
δν<SUB>02</SUB>/Δν and δν<SUB>01</SUB>/Δν have opposite trends
as a function of Δν. The data show a narrowing of the l = 1 ridge
toward lower ν<SUB>max</SUB>, in agreement with models predicting
more efficient mode trapping in stars with higher luminosity. We
investigate the offset epsilon in the asymptotic relation and find
a clear correlation with Δν, demonstrating that it is related
to fundamental stellar parameters. Finally, we present the first
amplitude-ν<SUB>max</SUB> relation for Kepler red giants. We observe
a lack of low-amplitude stars for ν<SUB>max</SUB> >~ 110 μHz
and find that, for a given ν<SUB>max</SUB> between 40 and 110 μHz,
stars with lower Δν (and consequently higher mass) tend to show
lower amplitudes than stars with higher Δν.
---------------------------------------------------------
Title: A Precise Asteroseismic Age and Radius for the Evolved Sun-like
Star KIC 11026764
Authors: Metcalfe, T. S.; Monteiro, M. J. P. F. G.; Thompson, M. J.;
Molenda-Żakowicz, J.; Appourchaux, T.; Chaplin, W. J.; Doǧan, G.;
Eggenberger, P.; Bedding, T. R.; Bruntt, H.; Creevey, O. L.; Quirion,
P. -O.; Stello, D.; Bonanno, A.; Silva Aguirre, V.; Basu, S.; Esch,
L.; Gai, N.; Di Mauro, M. P.; Kosovichev, A. G.; Kitiashvili, I. N.;
Suárez, J. C.; Moya, A.; Piau, L.; García, R. A.; Marques, J. P.;
Frasca, A.; Biazzo, K.; Sousa, S. G.; Dreizler, S.; Bazot, M.; Karoff,
C.; Frandsen, S.; Wilson, P. A.; Brown, T. M.; Christensen-Dalsgaard,
J.; Gilliland, R. L.; Kjeldsen, H.; Campante, T. L.; Fletcher, S. T.;
Handberg, R.; Régulo, C.; Salabert, D.; Schou, J.; Verner, G. A.;
Ballot, J.; Broomhall, A. -M.; Elsworth, Y.; Hekker, S.; Huber, D.;
Mathur, S.; New, R.; Roxburgh, I. W.; Sato, K. H.; White, T. R.;
Borucki, W. J.; Koch, D. G.; Jenkins, J. M.
2010ApJ...723.1583M Altcode: 2010arXiv1010.4329M
The primary science goal of the Kepler Mission is to provide
a census of exoplanets in the solar neighborhood, including the
identification and characterization of habitable Earth-like planets. The
asteroseismic capabilities of the mission are being used to determine
precise radii and ages for the target stars from their solar-like
oscillations. Chaplin et al. published observations of three bright
G-type stars, which were monitored during the first 33.5 days of science
operations. One of these stars, the subgiant KIC 11026764, exhibits a
characteristic pattern of oscillation frequencies suggesting that it
has evolved significantly. We have derived asteroseismic estimates of
the properties of KIC 11026764 from Kepler photometry combined with
ground-based spectroscopic data. We present the results of detailed
modeling for this star, employing a variety of independent codes and
analyses that attempt to match the asteroseismic and spectroscopic
constraints simultaneously. We determine both the radius and the age
of KIC 11026764 with a precision near 1%, and an accuracy near 2%
for the radius and 15% for the age. Continued observations of this
star promise to reveal additional oscillation frequencies that will
further improve the determination of its fundamental properties.
---------------------------------------------------------
Title: Stellar Imager (SI): developing and testing a predictive
dynamo model for the Sun by imaging other stars
Authors: Carpenter, Kenneth G.; Schrijver, Carolus J.; Karovska,
Margarita; Kraemer, Steve; Lyon, Richard; Mozurkewich, David;
Airapetian, Vladimir; Adams, John C.; Allen, Ronald J.; Brown, Alex;
Bruhweiler, Fred; Conti, Alberto; Christensen-Dalsgaard, Joergen;
Cranmer, Steve; Cuntz, Manfred; Danchi, William; Dupree, Andrea; Elvis,
Martin; Evans, Nancy; Giampapa, Mark; Harper, Graham; Hartman, Kathy;
Labeyrie, Antoine; Leitner, Jesse; Lillie, Chuck; Linsky, Jeffrey L.;
Lo, Amy; Mighell, Ken; Miller, David; Noecker, Charlie; Parrish, Joe;
Phillips, Jim; Rimmele, Thomas; Saar, Steve; Sasselov, Dimitar; Stahl,
H. Philip; Stoneking, Eric; Strassmeier, Klaus; Walter, Frederick;
Windhorst, Rogier; Woodgate, Bruce; Woodruff, Robert
2010arXiv1011.5214C Altcode:
The Stellar Imager mission concept is a space-based UV/Optical
interferometer designed to resolve surface magnetic activity and
subsurface structure and flows of a population of Sun-like stars,
in order to accelerate the development and validation of a predictive
dynamo model for the Sun and enable accurate long-term forecasting of
solar/stellar magnetic activity.
---------------------------------------------------------
Title: Asteroseismology of red giants from the first four months of
Kepler data: Fundamental stellar parameters
Authors: Kallinger, T.; Mosser, B.; Hekker, S.; Huber, D.; Stello,
D.; Mathur, S.; Basu, S.; Bedding, T. R.; Chaplin, W. J.; De Ridder,
J.; Elsworth, Y. P.; Frandsen, S.; García, R. A.; Gruberbauer, M.;
Matthews, J. M.; Borucki, W. J.; Bruntt, H.; Christensen-Dalsgaard,
J.; Gilliland, R. L.; Kjeldsen, H.; Koch, D. G.
2010A&A...522A...1K Altcode: 2010arXiv1010.4589K
Context. Clear power excess in a frequency range typical for solar-type
oscillations in red giants has been detected in more than 1000 stars,
which have been observed during the first 138 days of the science
operation of the NASA Kepler satellite. This sample includes stars in
a wide mass and radius range with spectral types G and K, extending
in luminosity from the bottom of the giant branch up to high-luminous
red giants, including the red bump and clump. The high-precision
asteroseismic observations with Kepler provide a perfect source
for testing stellar structure and evolutionary models, as well as
investigating the stellar population in our Galaxy. <BR /> Aims:
We aim to extract accurate seismic parameters from the Kepler time
series and use them to infer asteroseismic fundamental parameters
from scaling relations and a comparison with red-giant models. <BR />
Methods: We fit a global model to the observed power density spectra,
which allows us to accurately estimate the granulation background
signal and the global oscillation parameters, such as the frequency
of maximum oscillation power. We find regular patterns of radial and
non-radial oscillation modes and use a new technique to automatically
identify the mode degree and the characteristic frequency separations
between consecutive modes of the same spherical degree. In most
cases, we can also measure the small separation between l = 0, 1,
and 2 modes. Subsequently, the seismic parameters are used to estimate
stellar masses and radii and to place the stars in an H-R diagram by
using an extensive grid of stellar models that covers a wide parameter
range. Using Bayesian techniques throughout our entire analysis allows
us to determine reliable uncertainties for all parameters. <BR />
Results: We provide accurate seismic parameters and their uncertainties
for a large sample of red giants and determine their asteroseismic
fundamental parameters. We investigate the influence of the stars'
metallicities on their positions in the H-R diagram. Finally, we study
the red-giant populations in the red clump and bump and compare them
to a synthetic population. We find a mass and metallicity gradient in
the red clump and clear evidence of a secondary-clump population.
---------------------------------------------------------
Title: 2M1938+4603: a rich, multimode pulsating sdB star with an
eclipsing dM companion observed with Kepler
Authors: Østensen, R. H.; Green, E. M.; Bloemen, S.; Marsh, T. R.;
Laird, J. B.; Morris, M.; Moriyama, E.; Oreiro, R.; Reed, M. D.;
Kawaler, S. D.; Aerts, C.; Vučković, M.; Degroote, P.; Telting,
J. H.; Kjeldsen, H.; Gilliland, R. L.; Christensen-Dalsgaard, J.;
Borucki, W. J.; Koch, D.
2010MNRAS.408L..51O Altcode: 2010MNRAS.tmpL.126O; 2010arXiv1006.4267O
2M1938+4603 (KIC9472174) displays a spectacular light curve dominated
by a strong reflection effect and rather shallow, grazing eclipses. The
orbital period is 0.126 d, the second longest period yet found for an
eclipsing sdB+dM, but still close to the minimum 0.1-d period among
such systems. The phase-folded Kepler light curve was used to detrend
the orbital effects from the data set. The amplitude spectrum of the
residual light curve reveals a rich collection of pulsation peaks
spanning frequencies from ~50 to 4500μHz. The presence of a complex
pulsation spectrum in both the p- and g-mode regions has never before
been reported in a compact pulsator. <P />Eclipsing sdB+dM stars are
very rare, with only seven systems known and only one with a pulsating
primary. Pulsating stars in eclipsing binaries are especially important
since they permit masses derived from seismological model fits to be
cross-checked with orbital mass constraints. We present a first analysis
of this star based on the Kepler 9.7-d commissioning light curve and
extensive ground-based photometry and spectroscopy that allow us to
set useful bounds on the system parameters. We derive a radial-velocity
amplitude K<SUB>1</SUB> = 65.7 +/- 0.6 kms <SUP>-1</SUP>, inclination
angle , and find that the masses of the components are M<SUB>1</SUB>
= 0.48 +/- 0.03 M<SUB>solar</SUB> and M<SUB>2</SUB> = 0.12 +/- 0.01
M<SUB>solar</SUB>.
---------------------------------------------------------
Title: Early Asteroseismic Results from Kepler: Structural and Core
Parameters of the Hot B Subdwarf KPD 1943+4058 as Inferred from
g-mode Oscillations
Authors: Van Grootel, V.; Charpinet, S.; Fontaine, G.; Brassard,
P.; Green, E. M.; Randall, S. K.; Silvotti, R.; Østensen, R. H.;
Kjeldsen, H.; Christensen-Dalsgaard, J.; Borucki, W. J.; Koch, D.
2010ApJ...718L..97V Altcode:
We present a seismic analysis of the pulsating hot B subdwarf KPD
1943+4058 (KIC 005807616) on the basis of the long-period, gravity-mode
pulsations recently uncovered by Kepler. This is the first time that
g-mode seismology can be exploited quantitatively for stars on the
extreme horizontal branch, all previous successful seismic analyses
having been confined so far to short-period, p-mode pulsators. We
demonstrate that current models of hot B subdwarfs can quite well
explain the observed g-mode periods, while being consistent with
independent constraints provided by spectroscopy. We identify the
18 pulsations retained in our analysis as low-degree (ell = 1 and
2), intermediate-order (k = -9 through -58) g-modes. The periods
(frequencies) are recovered, on average, at the 0.22% level, which
is comparable to the best results obtained for p-mode pulsators. We
infer the following structural and core parameters for KPD 1943+4058
(formal fitting uncertainties only): T <SUB>eff</SUB> = 28,050
± 470 K, log g = 5.52 ± 0.03, M <SUB>*</SUB> = 0.496 ± 0.002 M
<SUB>sun</SUB>, log (M <SUB>env</SUB>/M <SUB>*</SUB>) = -2.55 ± 0.07,
log (1 - M <SUB>core</SUB>/M <SUB>*</SUB>) = -0.37 ± 0.01, and X
<SUB>core</SUB>(C+O) = 0.261 ± 0.008. We additionally derive the age
of the star since the zero-age extended horizontal branch 18.4 ± 1.0
Myr, the radius R = 0.203 ± 0.007 R <SUB>sun</SUB>, the luminosity L =
22.9 ± 3.13 L <SUB>sun</SUB>, the absolute magnitude M<SUB>V</SUB> =
4.21 ± 0.11, the reddening index E(B - V) = 0.094 ± 0.017, and the
distance d = 1180 ± 95 pc.
---------------------------------------------------------
Title: Asteroseismic modelling of the solar-like star β Hydri
Authors: Doğan, G.; Brandão, I. M.; Bedding, T. R.;
Christensen-Dalsgaard, J.; Cunha, M. S.; Kjeldsen, H.
2010Ap&SS.328..101D Altcode: 2009arXiv0912.3653D; 2009Ap&SS.tmp..251D
We present the results of modelling the subgiant star β Hydri using
seismic observational constraints. We have computed several grids of
stellar evolutionary tracks using the Aarhus STellar Evolution Code
(ASTEC, Christensen-Dalsgaard in Astrophys. Space Sci. 316:13, 2008a),
with and without helium diffusion and settling. For those models
on each track that are located at the observationally determined
position of β Hydri in the Hertzsprung-Russell (HR) diagram, we have
calculated the oscillation frequencies using the Aarhus adiabatic
pulsation package (ADIPLS, Christensen-Dalsgaard in Astrophys. Space
Sci. 316:113, 2008b). Applying the near-surface corrections to the
calculated frequencies using the empirical law presented by Kjeldsen
et al. (Astrophys. J. 683:L175, 2008), we have compared the corrected
model frequencies with the observed frequencies of the star. We show
that after correcting the frequencies for the near-surface effects, we
have a fairly good fit for both l=0 and l=2 frequencies. We also have
good agreement between the observed and calculated l=1 mode frequencies,
although there is room for improvement in order to fit all the observed
mixed modes simultaneously.
---------------------------------------------------------
Title: Prospects for asteroseismology
Authors: Christensen-Dalsgaard, Jørgen; Houdek, Günter
2010Ap&SS.328...51C Altcode: 2009Ap&SS.tmp..264C; 2009Ap&SS.tmp..287C; 2009Ap&SS.tmp..286C;
2009Ap&SS.tmp..276C; 2009arXiv0911.4629C
The observational basis for asteroseismology is being dramatically
strengthened, through more than two years of data from the CoRoT
satellite, the flood of data coming from the Kepler mission and, in
the slightly longer term, from dedicated ground-based facilities. Our
ability to utilize these data depends on further development
of techniques for basic data analysis, as well as on an improved
understanding of the relation between the observed frequencies and the
underlying properties of the stars. Also, stellar modelling must be
further developed, to match the increasing diagnostic potential of the
data. Here we discuss some aspects of data interpretation and modelling,
focusing on the important case of stars with solar-like oscillations.
---------------------------------------------------------
Title: Division v: Variable Stars
Authors: Gimenez, Alvaro; Kawaler, Steven; Christensen-Dalsgaard,
Jørgen; Breger, Michel; Guinan, Edward; Rucinski, Slavek
2010IAUTB..27..207G Altcode:
Division V organized a brief Business meeting during the XXVIIth
General Assembly, prior to Business meetings (reported separately)
of Commissions 27 and 42. The Division V Business Meeting began at
11:00 on 5 August 2009.
---------------------------------------------------------
Title: Asteroseismic Investigation of Known Planet Hosts in the
Kepler Field
Authors: Christensen-Dalsgaard, J.; Kjeldsen, H.; Brown, T. M.;
Gilliland, R. L.; Arentoft, T.; Frandsen, S.; Quirion, P. -O.; Borucki,
W. J.; Koch, D.; Jenkins, J. M.
2010ApJ...713L.164C Altcode: 2010arXiv1001.0032C
In addition to its great potential for characterizing extra-solar
planetary systems, the Kepler Mission is providing unique data on
stellar oscillations. A key aspect of Kepler asteroseismology is the
application to solar-like oscillations of main-sequence stars. As
an example, we here consider an initial analysis of data for three
stars in the Kepler field for which planetary transits were known
from ground-based observations. For one of these, HAT-P-7, we obtain
a detailed frequency spectrum and hence strong constraints on the
stellar properties. The remaining two stars show definite evidence
for solar-like oscillations, yielding a preliminary estimate of their
mean densities.
---------------------------------------------------------
Title: Detection of Solar-like Oscillations from Kepler Photometry
of the Open Cluster NGC 6819
Authors: Stello, Dennis; Basu, Sarbani; Bruntt, Hans; Mosser, Benoît;
Stevens, Ian R.; Brown, Timothy M.; Christensen-Dalsgaard, Jørgen;
Gilliland, Ronald L.; Kjeldsen, Hans; Arentoft, Torben; Ballot,
Jérôme; Barban, Caroline; Bedding, Timothy R.; Chaplin, William
J.; Elsworth, Yvonne P.; García, Rafael A.; Goupil, Marie-Jo;
Hekker, Saskia; Huber, Daniel; Mathur, Savita; Meibom, Søren;
Sangaralingam, Vinothini; Baldner, Charles S.; Belkacem, Kevin;
Biazzo, Katia; Brogaard, Karsten; Suárez, Juan Carlos; D'Antona,
Francesca; Demarque, Pierre; Esch, Lisa; Gai, Ning; Grundahl, Frank;
Lebreton, Yveline; Jiang, Biwei; Jevtic, Nada; Karoff, Christoffer;
Miglio, Andrea; Molenda-Żakowicz, Joanna; Montalbán, Josefina; Noels,
Arlette; Roca Cortés, Teodoro; Roxburgh, Ian W.; Serenelli, Aldo M.;
Silva Aguirre, Victor; Sterken, Christiaan; Stine, Peter; Szabó,
Robert; Weiss, Achim; Borucki, William J.; Koch, David; Jenkins, Jon M.
2010ApJ...713L.182S Altcode: 2010arXiv1001.0026S
Asteroseismology of stars in clusters has been a long-sought goal
because the assumption of a common age, distance, and initial chemical
composition allows strong tests of the theory of stellar evolution. We
report results from the first 34 days of science data from the Kepler
Mission for the open cluster NGC 6819—one of the four clusters in
the field of view. We obtain the first clear detections of solar-like
oscillations in the cluster red giants and are able to measure
the large frequency separation, Δν, and the frequency of maximum
oscillation power, ν<SUB>max</SUB>. We find that the asteroseismic
parameters allow us to test cluster membership of the stars, and
even with the limited seismic data in hand, we can already identify
four possible non-members despite their having a better than 80%
membership probability from radial velocity measurements. We are also
able to determine the oscillation amplitudes for stars that span about
2 orders of magnitude in luminosity and find good agreement with the
prediction that oscillation amplitudes scale as the luminosity to the
power of 0.7. These early results demonstrate the unique potential of
asteroseismology of the stellar clusters observed by Kepler.
---------------------------------------------------------
Title: Solar-like Oscillations in Low-luminosity Red Giants: First
Results from Kepler
Authors: Bedding, T. R.; Huber, D.; Stello, D.; Elsworth, Y. P.;
Hekker, S.; Kallinger, T.; Mathur, S.; Mosser, B.; Preston, H. L.;
Ballot, J.; Barban, C.; Broomhall, A. M.; Buzasi, D. L.; Chaplin,
W. J.; García, R. A.; Gruberbauer, M.; Hale, S. J.; De Ridder, J.;
Frandsen, S.; Borucki, W. J.; Brown, T.; Christensen-Dalsgaard, J.;
Gilliland, R. L.; Jenkins, J. M.; Kjeldsen, H.; Koch, D.; Belkacem,
K.; Bildsten, L.; Bruntt, H.; Campante, T. L.; Deheuvels, S.; Derekas,
A.; Dupret, M. -A.; Goupil, M. -J.; Hatzes, A.; Houdek, G.; Ireland,
M. J.; Jiang, C.; Karoff, C.; Kiss, L. L.; Lebreton, Y.; Miglio,
A.; Montalbán, J.; Noels, A.; Roxburgh, I. W.; Sangaralingam, V.;
Stevens, I. R.; Suran, M. D.; Tarrant, N. J.; Weiss, A.
2010ApJ...713L.176B Altcode: 2010arXiv1001.0229B
We have measured solar-like oscillations in red giants using
time-series photometry from the first 34 days of science operations
of the Kepler Mission. The light curves, obtained with 30 minute
sampling, reveal clear oscillations in a large sample of G and K
giants, extending in luminosity from the red clump down to the bottom
of the giant branch. We confirm a strong correlation between the large
separation of the oscillations (Δν) and the frequency of maximum power
(ν<SUB>max</SUB>). We focus on a sample of 50 low-luminosity stars
(ν<SUB>max</SUB> > 100 μHz, L <~ 30 L <SUB>sun</SUB>) having
high signal-to-noise ratios and showing the unambiguous signature
of solar-like oscillations. These are H-shell-burning stars, whose
oscillations should be valuable for testing models of stellar evolution
and for constraining the star formation rate in the local disk. We use a
new technique to compare stars on a single échelle diagram by scaling
their frequencies and find well-defined ridges corresponding to radial
and non-radial oscillations, including clear evidence for modes with
angular degree l = 3. Measuring the small separation between l = 0 and
l = 2 allows us to plot the so-called C-D diagram of δν<SUB>02</SUB>
versus Δν. The small separation δν<SUB>01</SUB> of l = 1 from
the midpoint of adjacent l = 0 modes is negative, contrary to the Sun
and solar-type stars. The ridge for l = 1 is notably broadened, which
we attribute to mixed modes, confirming theoretical predictions for
low-luminosity giants. Overall, the results demonstrate the tremendous
potential of Kepler data for asteroseismology of red giants.
---------------------------------------------------------
Title: Automated Classification of Variable Stars in the
Asteroseismology Program of the Kepler Space Mission
Authors: Blomme, J.; Debosscher, J.; De Ridder, J.; Aerts, C.;
Gilliland, R. L.; Christensen-Dalsgaard, J.; Kjeldsen, H.; Brown,
T. M.; Borucki, W. J.; Koch, D.; Jenkins, J. M.; Kurtz, D. W.; Stello,
D.; Stevens, I. R.; Suran, M. D.; Derekas, A.
2010ApJ...713L.204B Altcode: 2010arXiv1001.0507B
We present the first results of the application of supervised
classification methods to the Kepler Q1 long-cadence light curves of a
subsample of 2288 stars measured in the asteroseismology program of the
mission. The methods, originally developed in the framework of the CoRoT
and Gaia space missions, are capable of identifying the most common
types of stellar variability in a reliable way. Many new variables have
been discovered, among which a large fraction are eclipsing/ellipsoidal
binaries unknown prior to launch. A comparison is made between our
classification from the Kepler data and the pre-launch class based
on data from the ground, showing that the latter needs significant
improvement. The noise properties of the Kepler data are compared to
those of the exoplanet program of the CoRoT satellite. We find that
Kepler improves on CoRoT by a factor of 2-2.3 in point-to-point scatter.
---------------------------------------------------------
Title: Kepler Mission Design, Realized Photometric Performance,
and Early Science
Authors: Koch, David G.; Borucki, William J.; Basri, Gibor;
Batalha, Natalie M.; Brown, Timothy M.; Caldwell, Douglas;
Christensen-Dalsgaard, Jørgen; Cochran, William D.; DeVore, Edna;
Dunham, Edward W.; Gautier, Thomas N., III; Geary, John C.; Gilliland,
Ronald L.; Gould, Alan; Jenkins, Jon; Kondo, Yoji; Latham, David W.;
Lissauer, Jack J.; Marcy, Geoffrey; Monet, David; Sasselov, Dimitar;
Boss, Alan; Brownlee, Donald; Caldwell, John; Dupree, Andrea K.;
Howell, Steve B.; Kjeldsen, Hans; Meibom, Søren; Morrison, David;
Owen, Tobias; Reitsema, Harold; Tarter, Jill; Bryson, Stephen T.;
Dotson, Jessie L.; Gazis, Paul; Haas, Michael R.; Kolodziejczak,
Jeffrey; Rowe, Jason F.; Van Cleve, Jeffrey E.; Allen, Christopher;
Chandrasekaran, Hema; Clarke, Bruce D.; Li, Jie; Quintana, Elisa V.;
Tenenbaum, Peter; Twicken, Joseph D.; Wu, Hayley
2010ApJ...713L..79K Altcode: 2010arXiv1001.0268K
The Kepler Mission, launched on 2009 March 6, was designed with the
explicit capability to detect Earth-size planets in the habitable zone
of solar-like stars using the transit photometry method. Results from
just 43 days of data along with ground-based follow-up observations
have identified five new transiting planets with measurements of their
masses, radii, and orbital periods. Many aspects of stellar astrophysics
also benefit from the unique, precise, extended, and nearly continuous
data set for a large number and variety of stars. Early results for
classical variables and eclipsing stars show great promise. To fully
understand the methodology, processes, and eventually the results from
the mission, we present the underlying rationale that ultimately led
to the flight and ground system designs used to achieve the exquisite
photometric performance. As an example of the initial photometric
results, we present variability measurements that can be used to
distinguish dwarf stars from red giants.
---------------------------------------------------------
Title: First Kepler Results on RR Lyrae Stars
Authors: Kolenberg, K.; Szabó, R.; Kurtz, D. W.; Gilliland, R. L.;
Christensen-Dalsgaard, J.; Kjeldsen, H.; Brown, T. M.; Benkő,
J. M.; Chadid, M.; Derekas, A.; Di Criscienzo, M.; Guggenberger, E.;
Kinemuchi, K.; Kunder, A.; Kolláth, Z.; Kopacki, G.; Moskalik, P.;
Nemec, J. M.; Nuspl, J.; Silvotti, R.; Suran, M. D.; Borucki, W. J.;
Koch, D.; Jenkins, J. M.
2010ApJ...713L.198K Altcode: 2010arXiv1001.0417K
We present the first results of our analyses of selected RR Lyrae stars
for which data have been obtained by the Kepler Mission. As expected,
we find a significant fraction of the RRab stars to show the Blazhko
effect, a still unexplained phenomenon that manifests itself as periodic
amplitude and phase modulations of the light curve, on timescales of
typically tens to hundreds of days. The long time span of the Kepler
Mission of 3.5 yr and the unprecedentedly high precision of its data
provide a unique opportunity for the study of RR Lyrae stars. Using
data of a modulated star observed in the first roll as a showcase, we
discuss the data, our analyses, findings, and their implications for our
understanding of RR Lyrae stars and the Blazhko effect. With at least
40% of the RR Lyrae stars in our sample showing modulation, we confirm
the high incidence rate that was only found in recent high-precision
studies. Moreover, we report the occurrence of additional frequencies,
beyond the main pulsation mode and its modulation components. Their
half-integer ratio to the main frequency is reminiscent of a period
doubling effect caused by resonances, observed for the first time in
RR Lyrae stars.
---------------------------------------------------------
Title: Hybrid γ Doradus-δ Scuti Pulsators: New Insights into the
Physics of the Oscillations from Kepler Observations
Authors: Grigahcène, A.; Antoci, V.; Balona, L.; Catanzaro, G.;
Daszyńska-Daszkiewicz, J.; Guzik, J. A.; Handler, G.; Houdek,
G.; Kurtz, D. W.; Marconi, M.; Monteiro, M. J. P. F. G.; Moya, A.;
Ripepi, V.; Suárez, J. -C.; Uytterhoeven, K.; Borucki, W. J.; Brown,
T. M.; Christensen-Dalsgaard, J.; Gilliland, R. L.; Jenkins, J. M.;
Kjeldsen, H.; Koch, D.; Bernabei, S.; Bradley, P.; Breger, M.; Di
Criscienzo, M.; Dupret, M. -A.; García, R. A.; García Hernández, A.;
Jackiewicz, J.; Kaiser, A.; Lehmann, H.; Martín-Ruiz, S.; Mathias,
P.; Molenda-Żakowicz, J.; Nemec, J. M.; Nuspl, J.; Paparó, M.;
Roth, M.; Szabó, R.; Suran, M. D.; Ventura, R.
2010ApJ...713L.192G Altcode: 2010arXiv1001.0747G
Observations of the pulsations of stars can be used to infer their
interior structure and test theoretical models. The main-sequence
γ Doradus (Dor) and δ Scuti (Sct) stars with masses 1.2-2.5 M
<SUB>sun</SUB> are particularly useful for these studies. The γ
Dor stars pulsate in high-order g-modes with periods of order 1
day, driven by convective blocking at the base of their envelope
convection zone. The δ Sct stars pulsate in low-order g- and p-modes
with periods of order 2 hr, driven by the κ mechanism operating in
the He II ionization zone. Theory predicts an overlap region in the
Hertzsprung-Russell diagram between instability regions, where "hybrid"
stars pulsating in both types of modes should exist. The two types of
modes with properties governed by different portions of the stellar
interior provide complementary model constraints. Among the known γ
Dor and δ Sct stars, only four have been confirmed as hybrids. Now,
analysis of combined Quarter 0 and Quarter 1 Kepler data for hundreds of
variable stars shows that the frequency spectra are so rich that there
are practically no pure δ Sct or γ Dor pulsators, i.e., essentially
all of the stars show frequencies in both the δ Sct and the γ Dor
frequency range. A new observational classification scheme is proposed
that takes into account the amplitude as well as the frequency and is
applied to categorize 234 stars as δ Sct, γ Dor, δ Sct/γ Dor or
γ Dor/δ Sct hybrids.
---------------------------------------------------------
Title: A Multi-Site Campaign to Measure Solar-Like Oscillations in
Procyon. II. Mode Frequencies
Authors: Bedding, Timothy R.; Kjeldsen, Hans; Campante, Tiago L.;
Appourchaux, Thierry; Bonanno, Alfio; Chaplin, William J.; Garcia,
Rafael A.; Martić, Milena; Mosser, Benoit; Butler, R. Paul; Bruntt,
Hans; Kiss, László L.; O'Toole, Simon J.; Kambe, Eiji; Ando,
Hiroyasu; Izumiura, Hideyuki; Sato, Bun'ei; Hartmann, Michael;
Hatzes, Artie; Barban, Caroline; Berthomieu, Gabrielle; Michel,
Eric; Provost, Janine; Turck-Chièze, Sylvaine; Lebrun, Jean-Claude;
Schmitt, Jerome; Bertaux, Jean-Loup; Benatti, Serena; Claudi, Riccardo
U.; Cosentino, Rosario; Leccia, Silvio; Frandsen, Søren; Brogaard,
Karsten; Glowienka, Lars; Grundahl, Frank; Stempels, Eric; Arentoft,
Torben; Bazot, Michaël; Christensen-Dalsgaard, Jørgen; Dall, Thomas
H.; Karoff, Christoffer; Lundgreen-Nielsen, Jens; Carrier, Fabien;
Eggenberger, Patrick; Sosnowska, Danuta; Wittenmyer, Robert A.; Endl,
Michael; Metcalfe, Travis S.; Hekker, Saskia; Reffert, Sabine
2010ApJ...713..935B Altcode: 2010arXiv1003.0052B
We have analyzed data from a multi-site campaign to observe oscillations
in the F5 star Procyon. The data consist of high-precision velocities
that we obtained over more than three weeks with 11 telescopes. A
new method for adjusting the data weights allows us to suppress the
sidelobes in the power spectrum. Stacking the power spectrum in a
so-called échelle diagram reveals two clear ridges, which we identify
with even and odd values of the angular degree (l = 0 and 2, and l =
1 and 3, respectively). We interpret a strong, narrow peak at 446 μHz
that lies close to the l = 1 ridge as a mode with mixed character. We
show that the frequencies of the ridge centroids and their separations
are useful diagnostics for asteroseismology. In particular, variations
in the large separation appear to indicate a glitch in the sound-speed
profile at an acoustic depth of ~1000 s. We list frequencies for 55
modes extracted from the data spanning 20 radial orders, a range
comparable to the best solar data, which will provide valuable
constraints for theoretical models. A preliminary comparison with
published models shows that the offset between observed and calculated
frequencies for the radial modes is very different for Procyon than
for the Sun and other cool stars. We find the mean lifetime of the
modes in Procyon to be 1.29<SUP>+0.55</SUP> <SUB>-0.49</SUB> days,
which is significantly shorter than the 2-4 days seen in the Sun.
---------------------------------------------------------
Title: The Asteroseismic Potential of Kepler: First Results for
Solar-Type Stars
Authors: Chaplin, W. J.; Appourchaux, T.; Elsworth, Y.; García,
R. A.; Houdek, G.; Karoff, C.; Metcalfe, T. S.; Molenda-Żakowicz,
J.; Monteiro, M. J. P. F. G.; Thompson, M. J.; Brown, T. M.;
Christensen-Dalsgaard, J.; Gilliland, R. L.; Kjeldsen, H.; Borucki,
W. J.; Koch, D.; Jenkins, J. M.; Ballot, J.; Basu, S.; Bazot, M.;
Bedding, T. R.; Benomar, O.; Bonanno, A.; Brandão, I. M.; Bruntt,
H.; Campante, T. L.; Creevey, O. L.; Di Mauro, M. P.; Doǧan,
G.; Dreizler, S.; Eggenberger, P.; Esch, L.; Fletcher, S. T.;
Frandsen, S.; Gai, N.; Gaulme, P.; Handberg, R.; Hekker, S.; Howe,
R.; Huber, D.; Korzennik, S. G.; Lebrun, J. C.; Leccia, S.; Martic,
M.; Mathur, S.; Mosser, B.; New, R.; Quirion, P. -O.; Régulo, C.;
Roxburgh, I. W.; Salabert, D.; Schou, J.; Sousa, S. G.; Stello, D.;
Verner, G. A.; Arentoft, T.; Barban, C.; Belkacem, K.; Benatti, S.;
Biazzo, K.; Boumier, P.; Bradley, P. A.; Broomhall, A. -M.; Buzasi,
D. L.; Claudi, R. U.; Cunha, M. S.; D'Antona, F.; Deheuvels, S.;
Derekas, A.; García Hernández, A.; Giampapa, M. S.; Goupil, M. J.;
Gruberbauer, M.; Guzik, J. A.; Hale, S. J.; Ireland, M. J.; Kiss,
L. L.; Kitiashvili, I. N.; Kolenberg, K.; Korhonen, H.; Kosovichev,
A. G.; Kupka, F.; Lebreton, Y.; Leroy, B.; Ludwig, H. -G.; Mathis, S.;
Michel, E.; Miglio, A.; Montalbán, J.; Moya, A.; Noels, A.; Noyes,
R. W.; Pallé, P. L.; Piau, L.; Preston, H. L.; Roca Cortés, T.;
Roth, M.; Sato, K. H.; Schmitt, J.; Serenelli, A. M.; Silva Aguirre,
V.; Stevens, I. R.; Suárez, J. C.; Suran, M. D.; Trampedach, R.;
Turck-Chièze, S.; Uytterhoeven, K.; Ventura, R.; Wilson, P. A.
2010ApJ...713L.169C Altcode: 2010arXiv1001.0506C
We present preliminary asteroseismic results from Kepler on three G-type
stars. The observations, made at one-minute cadence during the first
33.5 days of science operations, reveal high signal-to-noise solar-like
oscillation spectra in all three stars: about 20 modes of oscillation
may be clearly distinguished in each star. We discuss the appearance of
the oscillation spectra, use the frequencies and frequency separations
to provide first results on the radii, masses, and ages of the stars,
and comment in the light of these results on prospects for inference
on other solar-type stars that Kepler will observe.
---------------------------------------------------------
Title: Near-surface effects and solar-age determination
Authors: Doğan, G.; Bonanno, A.; Christensen-Dalsgaard, J.
2010arXiv1004.2215D Altcode:
The dominant part of the difference between the observed and model
frequencies of the Sun can be approximated by a power law. We show that
when this empirical law is employed to correct the model frequencies
and then the small frequency separations are used for solar age
determination, the results are consistent with the meteoritic age
(4.563 Gyr < t < 4.576 Gyr). We present the results and compare
with those obtained by using the ratios of small to large frequency
separations.
---------------------------------------------------------
Title: Discovery of a Red Giant with Solar-like Oscillations in an
Eclipsing Binary System from Kepler Space-based Photometry
Authors: Hekker, S.; Debosscher, J.; Huber, D.; Hidas, M. G.; De
Ridder, J.; Aerts, C.; Stello, D.; Bedding, T. R.; Gilliland, R. L.;
Christensen-Dalsgaard, J.; Brown, T. M.; Kjeldsen, H.; Borucki, W. J.;
Koch, D.; Jenkins, J. M.; Van Winckel, H.; Beck, P. G.; Blomme,
J.; Southworth, J.; Pigulski, A.; Chaplin, W. J.; Elsworth, Y. P.;
Stevens, I. R.; Dreizler, S.; Kurtz, D. W.; Maceroni, C.; Cardini,
D.; Derekas, A.; Suran, M. D.
2010ApJ...713L.187H Altcode: 2010arXiv1001.0399H
Oscillating stars in binary systems are among the most interesting
stellar laboratories, as these can provide information on the stellar
parameters and stellar internal structures. Here we present a red
giant with solar-like oscillations in an eclipsing binary observed
with the NASA Kepler satellite. We compute stellar parameters of the
red giant from spectra and the asteroseismic mass and radius from
the oscillations. Although only one eclipse has been observed so far,
we can already determine that the secondary is a main-sequence F star
in an eccentric orbit with a semi-major axis larger than 0.5 AU and
orbital period longer than 75 days.
---------------------------------------------------------
Title: Kepler Asteroseismology Program: Introduction and First Results
Authors: Gilliland, Ronald L.; Brown, Timothy M.;
Christensen-Dalsgaard, Jørgen; Kjeldsen, Hans; Aerts, Conny;
Appourchaux, Thierry; Basu, Sarbani; Bedding, Timothy R.; Chaplin,
William J.; Cunha, Margarida S.; De Cat, Peter; De Ridder, Joris;
Guzik, Joyce A.; Handler, Gerald; Kawaler, Steven; Kiss, László;
Kolenberg, Katrien; Kurtz, Donald W.; Metcalfe, Travis S.; Monteiro,
Mario J. P. F. G.; Szabó, Robert; Arentoft, Torben; Balona, Luis;
Debosscher, Jonas; Elsworth, Yvonne P.; Quirion, Pierre-Olivier;
Stello, Dennis; Suárez, Juan Carlos; Borucki, William J.; Jenkins,
Jon M.; Koch, David; Kondo, Yoji; Latham, David W.; Rowe, Jason F.;
Steffen, Jason H.
2010PASP..122..131G Altcode: 2010arXiv1001.0139G
Asteroseismology involves probing the interiors of stars and quantifying
their global properties, such as radius and age, through observations of
normal modes of oscillation. The technical requirements for conducting
asteroseismology include ultrahigh precision measured in photometry
in parts per million, as well as nearly continuous time series over
weeks to years, and cadences rapid enough to sample oscillations with
periods as short as a few minutes. We report on results from the first
43 days of observations, in which the unique capabilities of Kepler
in providing a revolutionary advance in asteroseismology are already
well in evidence. The Kepler asteroseismology program holds intrinsic
importance in supporting the core planetary search program through
greatly enhanced knowledge of host star properties, and extends well
beyond this to rich applications in stellar astrophysics.
---------------------------------------------------------
Title: Sounding stellar cycles with Kepler - preliminary results
from ground-based chromospheric activity measurements†
Authors: Karoff, C.; Metcalfe, T. S.; Chaplin, W. J.; Frandsen,
S.; Grundahl, F.; Kjeldsen, H.; Buzasi, D.; Arentoft, T.;
Christensen-Dalsgaard, J.
2010IAUS..264...57K Altcode: 2009arXiv0910.1436K
Due to its unique long-term coverage and high photometric precision,
observations from the Kepler asteroseismic investigation will provide us
with the possibility to sound stellar cycles in a number of solar-type
stars with asteroseismology. By comparing these measurements with
conventional ground-based chromospheric activity measurements we
might be able to increase our understanding of the relation between
the chromospheric changes and the changes in the eigenmodes. <P />In
parallel with the Kepler observations we have therefore started a
programme at the Nordic Optical Telescope to observe and monitor
chromospheric activity in the stars that are most likely to be
selected for observations for the whole satellite mission. The
ground-based observations presented here can be used both to guide
the selection of the special Kepler targets and as the first step in
a monitoring programme for stellar cycles. Also, the chromospheric
activity measurements obtained from the ground-based observations can
be compared with stellar parameters such as ages and rotation in order
to improve stellar evolution models.
---------------------------------------------------------
Title: Kepler Planet-Detection Mission: Introduction and First Results
Authors: Borucki, William J.; Koch, David; Basri, Gibor; Batalha,
Natalie; Brown, Timothy; Caldwell, Douglas; Caldwell, John;
Christensen-Dalsgaard, Jørgen; Cochran, William D.; DeVore, Edna;
Dunham, Edward W.; Dupree, Andrea K.; Gautier, Thomas N.; Geary, John
C.; Gilliland, Ronald; Gould, Alan; Howell, Steve B.; Jenkins, Jon M.;
Kondo, Yoji; Latham, David W.; Marcy, Geoffrey W.; Meibom, Søren;
Kjeldsen, Hans; Lissauer, Jack J.; Monet, David G.; Morrison, David;
Sasselov, Dimitar; Tarter, Jill; Boss, Alan; Brownlee, Don; Owen,
Toby; Buzasi, Derek; Charbonneau, David; Doyle, Laurance; Fortney,
Jonathan; Ford, Eric B.; Holman, Matthew J.; Seager, Sara; Steffen,
Jason H.; Welsh, William F.; Rowe, Jason; Anderson, Howard; Buchhave,
Lars; Ciardi, David; Walkowicz, Lucianne; Sherry, William; Horch,
Elliott; Isaacson, Howard; Everett, Mark E.; Fischer, Debra; Torres,
Guillermo; Johnson, John Asher; Endl, Michael; MacQueen, Phillip;
Bryson, Stephen T.; Dotson, Jessie; Haas, Michael; Kolodziejczak,
Jeffrey; Van Cleve, Jeffrey; Chandrasekaran, Hema; Twicken, Joseph
D.; Quintana, Elisa V.; Clarke, Bruce D.; Allen, Christopher; Li,
Jie; Wu, Haley; Tenenbaum, Peter; Verner, Ekaterina; Bruhweiler,
Frederick; Barnes, Jason; Prsa, Andrej
2010Sci...327..977B Altcode:
The Kepler mission was designed to determine the frequency of
Earth-sized planets in and near the habitable zone of Sun-like
stars. The habitable zone is the region where planetary temperatures
are suitable for water to exist on a planet’s surface. During the
first 6 weeks of observations, Kepler monitored 156,000 stars, and
five new exoplanets with sizes between 0.37 and 1.6 Jupiter radii and
orbital periods from 3.2 to 4.9 days were discovered. The density of
the Neptune-sized Kepler-4b is similar to that of Neptune and GJ 436b,
even though the irradiation level is 800,000 times higher. Kepler-7b
is one of the lowest-density planets (~0.17 gram per cubic centimeter)
yet detected. Kepler-5b, -6b, and -8b confirm the existence of planets
with densities lower than those predicted for gas giant planets.
---------------------------------------------------------
Title: The Kepler Mission and Early Results
Authors: Koch, David; Borucki, William; Jenkins, Jon; Basri,
Gibor; Batalha, Natalie M.; Brown, Timothy M.; Caldwell, Douglas;
Christensen-Dalsgaard, Jørgen; Cochran, William D.; Devore, Edna;
Dunham, Edward W.; Gautier, Thomas N., III; Geary, John C.; Gilliland,
Ronald L.; Gould, Alan; Jenkins, Jon; Latham, David W.; Lissauer,
Jack J.; Marcy, Geoffrey; Monet, David; Sasselov, Dimitar; Boss, Alan;
Caldwell, John; Dupree, Andrea K.; Howell, Steve B.; Kjeldsen, Hans;
Meibom, Søren; Morrison, David; Tarter, Jill; Bryson, Stephen T.;
Dotson, Jessie L.; Haas, Michael R.; Kolodziejczak, Jeffrey; Rowe,
Jason F.; van Cleve, Jeffrey E.; Buzasi, Derek; Charbonneau, David;
Doyle, Lau-Rance; Ford, Eric; Fortney, Jonathan; Holman, Matthew;
Seager, Sara; Steffen, Jason; Welsh, William
2010cosp...38.2513K Altcode: 2010cosp.meet.2513K
Kepler is a Discovery-class mission designed to determine the frequency
of Earth-size planets in and near the habitable zone of solar-like
stars. The instrument consists of a 0.95 m aperture photometer designed
to obtain high-precision photometric measurement for more than 3.5
years of more than 100,000 stars to search for patterns of transits
of exoplanets. The focal plane of the Schmidt telescope contains 42
CCDs with a total of 95 megapixels that cover 115 square degrees of
sky. The single star field will be viewed for the entire duration
of the mission. The photometer was launched into an Earth-trailing
heliocentric orbit on March 6, 2009, finished its commissioning on May
12, and is now in the science operations mode. The bases for a number of
the design choices are described. Although the data have not yet been
fully corrected for the presence of systematic errors and artifacts,
the data show the presence of thousands of eclipsing binaries and
variable stars of amazing variety. The character of stellar variability
allows us to distinguish dwarf stars from giants. Astrometric stability
at the sub-millipixel level of the photocenters of stars allows us in
many cases to distinguish transit candidates from background eclipsing
binaries. Analysis of the early data shows transits, occultations and
even visible light emission from the hot exoplanet HAT-P-7b. The latest
results on exoplanet detections from Kepler will be presented. Funding
for this mission is provided by NASA's Science Mission Directorate.
---------------------------------------------------------
Title: Asteroseismology
Authors: Aerts, Conny; Christensen-Dalsgaard, Jørgen; Kurtz, Donald W.
2010aste.book.....A Altcode:
The recent research domain of asteroseismology studies the internal
structure of stars, which is not directly observable, through the
interpretation of the frequency spectra of stellar oscillations. The
basic principles of asteroseismology are very similar to those
developed by earth seismologists. Stellar interiors can be probed from
oscillations because different oscillation modes penetrate to different
depths inside the star. Asteroseismology is the only available method
to derive the internal structure of the stars with high precision. <P
/>This book - the first on asteroseismology - offers a practical guide
for graduate students and scientists working in stellar astrophysics. It
provides a general introduction to asteroseismology and comprehensive
coverage of all its aspects: fundamental theory, observations and
observational techniques, methodology of data analysis and seismic
interpretations of various classes of multi-periodic pulsating stars.
---------------------------------------------------------
Title: Kepler Planet Detection Mission: Introduction and First Results
Authors: Borucki, William J.; Koch, D.; Basri, G.; Batalha, N. M.;
Brown, T.; Caldwell, D. A.; Caldwell, J.; Christensen-Dalsgaard, J.;
Cochran, W.; DeVore, E.; Dunham, E.; Dupree, A.; Gautier, T.; Geary,
J.; Gilliland, R.; Gould, A.; Howell, S.; Jenkins, J.; Kjeldsen, H.;
Kondo, Y.; Latham, D.; Lissauer, J.; Marcy, G.; Meibom, S.; Monet,
D.; Morrison, D.; Sasselov, D.; Tarter, J.
2010AAS...21510101B Altcode: 2010BAAS...42..215B
The Kepler Mission is designed to determine the frequency of Earth-size
and terrestrial size planets in and near the HZ of solar-like stars. It
was competitively selected as Discovery Mission #10 and launched on
March 6, 2009. Since completion of commissioning, it has continuously
observed over 145,000 main sequence stars. The photometric precision
reaches 20 ppm for 12<SUP>th</SUP> magnitude stars on the least
noisy detectors in 6.5 hours. During the first month of operation,
the photometer detected transit-like signatures from over 100
stars. Careful examination of these events shows many of them to
be false-positives such as background eclipsing binaries. However
ground-based follow up observations confirm the discovery of exoplanets
with sizes ranging from 0.6 Rj to1.5Rj and orbital periods ranging
from 3 to 9 days. Observations at Keck, Hobby-Eberly, Harlan-Smith,
WIYN, MMT, Tillighast, Shane, and Nordic Optic telescopes are vetting
many of the candidates and measuring their masses. Discovery of the
HAT-P7b occultation will be used to derive atmospheric properties
and demonstrates the precision necessary to detect Earth-size
planets. Asteroseismic analyses of several stars show the presence
of p-mode oscillations that can be used to determine stellar size
and age. This effort is being organized by the Kepler Asteroseismic
Science Consortium at Aarhus University in Denmark. Stellar parallaxes
are determined from the centroid motion of the stellar images and will
be combined with photometric measurements to get the sizes of stars
too dim for asteroseismic measurement. Four open clusters are being
observed to determine rotation rates with stellar age and spectral
type. Many types of stellar variability are observed with unprecedented
precision and over long continuous time periods. Examples of many of
these discoveries are presented. Funding by the Exoplanet Exploration
Program of the NASA Astrophysics Division is gratefully acknowledged.
---------------------------------------------------------
Title: The Kepler Short Cadence Data and Applications for
Asteroseismology and Transit Light Curves
Authors: Gilliland, Ronald L.; Brown, T. M.; Christensen-Dalsgaard,
J.; Kjeldsen, H.; Borucki, W. J.; Bryson, S.; Caldwell, D. A.; Jenkins,
J. M.; Koch, D.; Kepler Team
2010AAS...21530504G Altcode: 2010BAAS...42..302G
The Kepler data acquisition allows 512 targets to be followed in a
'short cadence' mode with roughly 1-minute integrations as needed for
asteroseismology of solar analogs having p-mode oscillations of a few
minutes, and to study fine details of high S/N transits. Characteristics
of these data will be described. An application of asteroseismology in
support of the core Kepler mission of characterizing detected planets
follows from stellar radius determinations needed to in turn provide
radii for the planets. The steps from processing of Kepler short cadence
data, derivation of asteroseismic frequencies from power spectra of
these time series, constraint on the mean stellar density and ultimately
stellar radius will be illustrated for a few planet host stars yielding
radii to accuracies approaching 1%. Analysis of individual oscillation
frequencies will provide information about the properties of stellar
interiors, resulting in some cases in determinations of ages to about
10%. Asteroseismic results will ultimately be expected for several
thousand stars ranging from the solar analog oscillations mentioned
above, to oscillations in red giants and a full spectrum of classical
variable stars (both at short, and the 30-minute long cadence) including
delta Scuti, RR Lyrae, RoAp stars etc. <P />Kepler was selected as
the 10th mission of the Discovery Program. Funding for this mission
is provided by NASA, Science Mission Directorate.
---------------------------------------------------------
Title: The internal dynamics and magnetism of the sun -- the
perspective from global helioseismology (Invited)
Authors: Howe, R.; Hill, F.; Komm, R.; Christensen-Dalsgaard, J.;
Schou, J.; Thompson, M. J.
2009AGUFMSH11B..04H Altcode:
Helioseismology allows us to probe the interior dynamics of the
Sun. Observations over the past three decades reveal the interior
rotation profile, with a near-surface shear layer, differential
rotation throughout the convection zone, a strong shear layer -- the
tachocline -- at the base of the convection zone, and approximately
uniform rotation in the radiative interior. Since the mid 1990's,
continuous observations from the Global Oscillations Network Group and
the Michelson Doppler Imager have allowed the study of subtle temporal
variations in the rotation within the convection zone. The so-called
"torsional oscillation" pattern of migrating zonal flows accompanying
the surface activity migration during the solar cycle has been shown to
penetrate deep within the convection zone. During the current extended
solar minimum, the flow bands can be seen to migrate more slowly towards
the equator than was seen in the previous minimum. There have also been
(still unconfirmed) findings of shorter-term variations in the rotation
rate close to the tachocline during the early years of the previous
solar cycle. This review will describe the important results and give
an update on the most recent observations of the interior dynamics as
we await the rise of solar cycle 24.
---------------------------------------------------------
Title: The Stellar Observations Network Group—the Prototype
Authors: Grundahl, F.; Christensen-Dalsgaard, J.; Kjeldsen, H.;
Jørgensen, U. G.; Arentoft, T.; Frandsen, S.; Kjærgaard, P.
2009ASPC..416..579G Altcode: 2009arXiv0908.0436G
The Stellar Observations Network Group (SONG) has obtained full
funding for the design, construction and implementation of a prototype
telescope and instrumentation package for the first network node. We
describe the layout of such a node and its instrumentation and expected
performance for radial-velocity measurements. The instrumentation
consists of a 1m telescope, equipped with two cameras for photometry
of microlensing events with the lucky-imaging technique and a
high-resolution spectrograph equipped with an iodine cell for obtaining
high-precision radial velocities of solar-like stars, in order to do
asteroseismology. The telescope will be located in a dome of ∼4.5 m
diameter, with two lucky-imaging cameras at one of the Nasmyth foci and
the spectrograph and instrument control computers at a Coudé focus,
located in an adjacent container. Currently the prototype telescope
and instrumentation is undergoing detailed design. Installation at
the first site (Tenerife) is expected during mid-late 2010, followed
by extensive testing during 2011.
---------------------------------------------------------
Title: Open issues in stellar modelling
Authors: Christensen-Dalsgaard, J.
2009arXiv0912.1405C Altcode:
An important goal of helio- and asteroseismology is to improve the
modelling of stellar evolution. Here I provide a brief discussion
of some of the uncertain issues in stellar modelling, of possible
relevance to asteroseismic inferences.
---------------------------------------------------------
Title: The Torsional Oscillation and the Solar Minimum
Authors: Howe, R.; Hill, F.; Komm, R.; Christensen-Dalsgaard, J.;
Schou, J.; Thompson, M. J.
2009AGUFM.U34A..03H Altcode:
The so-called torsional oscillation is a pattern of zonal flow bands,
detected at the solar surface by direct Doppler measurements and within
the convection zone by helioseismic measurements such as those carried
out by the Global Oscillations Network Group and the Michelson Doppler
Imager, that migrates from mid-latitudes towards the equator and poles
with each solar cycle. In the current minimum the low-latitude branch
of the pattern can be seen to have taken at least a year longer to
migrate towards the equator than was the case in the previous minimum. A
flow configuration matching that of the previous minimum was reached
during 2008, and by early 2009 the fast-rotating belt associated with
the new cycle had reached the latitude at which the onset of activity
was seen in Cycle 23, but magnetic activity has remained low. We will
present the most recent results and consider the implications for the
new solar cycle.
---------------------------------------------------------
Title: A Stellar Model-fitting Pipeline for Solar-like Oscillations
Authors: Metcalfe, T. S.; Creevey, O. L.; Christensen-Dalsgaard, J.
2009AIPC.1170..535M Altcode: 2009arXiv0906.4317M
Over the past two decades, helioseismology has revolutionized
our understanding of the interior structure and dynamics of the
Sun. Asteroseismology will soon place this knowledge into a broader
context by providing structural data for hundreds of Sun-like
stars. Solar-like oscillations have already been detected from the
ground in several stars, and NASA's Kepler mission is poised to unleash
a flood of stellar pulsation data. Deriving reliable asteroseismic
information from these observations demands a significant improvement in
our analysis methods. We report the initial results of our efforts to
develop an objective stellar model-fitting pipeline for asteroseismic
data. The cornerstone of our automated approach is an optimization
method using a parallel genetic algorithm. We describe the details of
the pipeline and we present the initial application to Sun-as-a-star
data, yielding an optimal model that accurately reproduces the known
solar properties.
---------------------------------------------------------
Title: Radial Pulsations in A Stars: the Effects of Opacity
Fluctuations in their Atmospheres
Authors: Medupe, R.; Christensen-Dalsgaard, J.; Phorah, M.
2009AIPC.1170..506M Altcode:
We investigate the effect of pulsational opacity fluctuations in the
atmospheres of A star models and show that the opacity fluctuations
are responsible for the “bump” often seen in the temperature
eigenfunctions in the region of the hydrogen ionization zone. We
also present a formula that relates perturbations in the surface
flux to those in effective temperature (Teff). This formula shows
that for cooler A stars, opacity fluctuations can introduce a phase
difference between δH(0)/H(0) and δTeff/Teff. In addition the new
formula is used to calculate multicolour pulsational amplitudes that
can be compared with photometric data to perform mode discrimination.
---------------------------------------------------------
Title: A Note on the Torsional Oscillation at Solar Minimum
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R.;
Schou, J.; Thompson, M. J.
2009ApJ...701L..87H Altcode: 2009arXiv0907.2965H
We examine the evolution of the zonal flow pattern in the upper solar
convection zone during the current extended solar minimum, and compare
it with that during the previous minimum. The results suggest that
a configuration matching that at the previous minimum was reached
during 2008, but that the flow band corresponding to the new cycle has
been moving more slowly toward the equator than was observed in the
previous cycle, resulting in a gradual increase in the apparent length
of the cycle during the 2007-2008 period. The current position of the
lower-latitude fast-rotating belt corresponds to that seen around the
onset of activity in the previous cycle.
---------------------------------------------------------
Title: Kepler’s Optical Phase Curve of the Exoplanet HAT-P-7b
Authors: Borucki, W. J.; Koch, D.; Jenkins, J.; Sasselov, D.;
Gilliland, R.; Batalha, N.; Latham, D. W.; Caldwell, D.; Basri, G.;
Brown, T.; Christensen-Dalsgaard, J.; Cochran, W. D.; DeVore, E.;
Dunham, E.; Dupree, A. K.; Gautier, T.; Geary, J.; Gould, A.; Howell,
S.; Kjeldsen, H.; Lissauer, J.; Marcy, G.; Meibom, S.; Morrison, D.;
Tarter, J.
2009Sci...325..709B Altcode:
Ten days of photometric data were obtained during the commissioning
phase of the Kepler mission, including data for the previously known
giant transiting exoplanet HAT-P-7b. The data for HAT-P-7b show a
smooth rise and fall of light from the planet as it orbits its star,
punctuated by a drop of 130 ± 11 parts per million in flux when the
planet passes behind its star. We interpret this as the phase variation
of the dayside thermal emission plus reflected light from the planet
as it orbits its star and is occulted. The depth of the occultation
is similar in importance to the detection of a transiting Earth-size
planet for which the mission was designed.
---------------------------------------------------------
Title: Radius Determination of Solar-type Stars Using
Asteroseismology: What to Expect from the Kepler Mission
Authors: Stello, Dennis; Chaplin, William J.; Bruntt, Hans; Creevey,
Orlagh L.; García-Hernández, Antonio; Monteiro, Mario J. P. F. G.;
Moya, Andrés; Quirion, Pierre-Olivier; Sousa, Sergio G.; Suárez,
Juan-Carlos; Appourchaux, Thierry; Arentoft, Torben; Ballot, Jerome;
Bedding, Timothy R.; Christensen-Dalsgaard, Jørgen; Elsworth,
Yvonne; Fletcher, Stephen T.; García, Rafael A.; Houdek, Günter;
Jiménez-Reyes, Sebastian J.; Kjeldsen, Hans; New, Roger; Régulo,
Clara; Salabert, David; Toutain, Thierry
2009ApJ...700.1589S Altcode: 2009arXiv0906.0766S
For distant stars, as observed by the NASA Kepler satellite,
parallax information is currently of fairly low quality and is not
complete. This limits the precision with which the absolute sizes of
the stars and their potential transiting planets can be determined by
traditional methods. Asteroseismology will be used to aid the radius
determination of stars observed during NASA's Kepler mission. We
report on the recent asteroFLAG hare-and-hounds Exercise#2, where
a group of "hares" simulated data of F-K main-sequence stars that a
group of "hounds" sought to analyze, aimed at determining the stellar
radii. We investigated stars in the range 9 < V < 15, both
with and without parallaxes. We further test different uncertainties
in T <SUB>eff</SUB>, and compare results with and without using
asteroseismic constraints. Based on the asteroseismic large frequency
spacing, obtained from simulations of 4 yr time series data from
the Kepler mission, we demonstrate that the stellar radii can be
correctly and precisely determined, when combined with traditional
stellar parameters from the Kepler Input Catalogue. The radii found
by the various methods used by each independent hound generally agree
with the true values of the artificial stars to within 3%, when the
large frequency spacing is used. This is 5-10 times better than the
results where seismology is not applied. These results give strong
confidence that radius estimation can be performed to better than 3%
for solar-like stars using automatic pipeline reduction. Even when the
stellar distance and luminosity are unknown we can obtain the same level
of agreement. Given the uncertainties used for this exercise we find
that the input log g and parallax do not help to constrain the radius,
and that T <SUB>eff</SUB> and metallicity are the only parameters we
need in addition to the large frequency spacing. It is the uncertainty
in the metallicity that dominates the uncertainty in the radius.
---------------------------------------------------------
Title: A Stellar Model-fitting Pipeline for Asteroseismic Data from
the Kepler Mission
Authors: Metcalfe, T. S.; Creevey, O. L.; Christensen-Dalsgaard, J.
2009ApJ...699..373M Altcode: 2009arXiv0903.0616M
Over the past two decades, helioseismology has revolutionized
our understanding of the interior structure and dynamics of the
Sun. Asteroseismology will soon place this knowledge into a broader
context by providing structural data for hundreds of Sun-like
stars. Solar-like oscillations have already been detected from the
ground in several stars, and NASA's Kepler mission is poised to unleash
a flood of stellar pulsation data. Deriving reliable asteroseismic
information from these observations demands a significant improvement
in our analysis methods. In this paper, we report the initial results
of our efforts to develop an objective stellar model-fitting pipeline
for asteroseismic data. The cornerstone of our automated approach is
an optimization method using a parallel genetic algorithm. We describe
the details of the pipeline and we present the initial application to
Sun-as-a-star data, yielding an optimal model that accurately reproduces
the known solar properties.
---------------------------------------------------------
Title: Concluding remarks
Authors: Christensen-Dalsgaard, J.
2009CoAst.158..356C Altcode:
The 38<SUP>th</SUP> Liège Colloquium covered a broad range
of topics within the area of massive stars on and near the main
sequence. This included the physical processes in stellar interiors
and modelling of stellar evolution, as well as observational aspects
with emphasis on asteroseismology and the potential of recent and
coming observations. This was a fitting tribute to Arlette Noels on
the occasion of her retirement. Here I provide a brief summary of some
of the main points of the conference.
---------------------------------------------------------
Title: Composing the verses for SONG
Authors: Grundahl, F.; Christensen-Dalsgaard, J.; Arentoft, T.;
Frandsen, S.; Kjeldsen, H.; Jørgensen, U. G.; Kjærgaard, P.
2009CoAst.158..345G Altcode:
The SONG (Stellar Observations Network Group) project aims at designing
and building a global network of 1m telescopes. The primary science
goals are to detect extra--solar planets (using the microlensing
and radial velocity techniques) and study stellar interiors using
asteroseismology. In early 2008 funding was obtained to construct a
prototype network node (telescope, dome, instrumentation and software)
to be ready by the end of 2011. Here we give an account of the project
and the expected broad structure of the network nodes.
---------------------------------------------------------
Title: The Kepler mission
Authors: Christensen-Dalsgaard, J.; Arentoft, T.; Brown, T. M.;
Gilliland, R. L.; Kjeldsen, H.; Borucki, W. J.; Koch, D.
2009CoAst.158..328C Altcode:
The Kepler mission will provide a vast improvement in the
characterization of extrasolar planetary systems, and in addition give
a dramatic increase in the data available for asteroseismology. The
present paper gives a brief overview of the mission, emphasizing
the asteroseismic aspects, and with references to more detailed
presentations.
---------------------------------------------------------
Title: The Sun as a fundamental calibrator of stellar evolution
Authors: Christensen-Dalsgaard, Jørgen
2009IAUS..258..431C Altcode: 2009arXiv0904.0358C
The Sun is unique amongst stars in having a precisely
determined age which does not depend on the modelling of stellar
evolution. Furthermore, other global properties of the Sun are known
to much higher accuracy than for any other star. Also, helioseismology
has provided detailed determination of the solar internal structure and
rotation. As a result, the Sun plays a central role in the development
and test of stellar modelling. Here I discuss solar modelling and
its application to tests of asteroseismic techniques for stellar age
determination.
---------------------------------------------------------
Title: Measurements of Stellar Properties through Asteroseismology:
A Tool for Planet Transit Studies
Authors: Kjeldsen, Hans; Bedding, Timothy R.; Christensen-Dalsgaard,
Jørgen
2009IAUS..253..309K Altcode: 2008arXiv0807.0508K
Oscillations occur in stars of most masses and essentially all stages
of evolution. Asteroseismology is the study of the frequencies and
other properties of stellar oscillations, from which we can extract
fundamental parameters such as density, mass, radius, age and rotation
period. We present an overview of asteroseismic analysis methods,
focusing on how this technique may be used as a tool to measure stellar
properties relevant to planet transit studies. We also discuss details
of the Kepler Asteroseismic Investigation the use of asteroseismology
on the Kepler mission in order to measure basic stellar parameters. We
estimate that applying asteroseismology to stars observed by Kepler will
allow the determination of stellar mean densities to an accuracy of 1%,
radii to 2 3%, masses to 5%, and ages to 5 10% of the main-sequence
lifetime. For rotating stars, the angle of inclination can also be
determined.
---------------------------------------------------------
Title: KEPLER: Search for Earth-Size Planets in the Habitable Zone
Authors: Borucki, William; Koch, David; Batalha, Natalie; Caldwell,
Douglas; Christensen-Dalsgaard, Jorgen; Cochran, William D.; Dunham,
Edward; Gautier, Thomas N.; Geary, John; Gilliland, Ronald; Jenkins,
Jon; Kjeldsen, Hans; Lissauer, Jack J.; Rowe, Jason
2009IAUS..253..289B Altcode:
The Kepler Mission is a space-based mission whose primary goal is
to determine the frequency of Earth-size and larger planets in the
habitable zone of solar-like stars. The mission will monitor more than
100,000 stars for patterns of transits with a differential photometric
precision of 20 ppm at V = 12 for a 6.5 hour transit. It will also
provide asteroseismic results on several thousand dwarf stars. It is
specifically designed to continuously observe a single field of view
of greater than 100 square degrees for 3.5 or more years. <P />This
paper provides a short overview of the mission, a brief history of
the mission development, expected results, new investigations by the
recently chosen Participating Scientists, and the plans for the Guest
Observer and Astrophysical Data Programs.
---------------------------------------------------------
Title: Solar-like oscillations in the G8 V star τ Ceti
Authors: Teixeira, T. C.; Kjeldsen, H.; Bedding, T. R.; Bouchy, F.;
Christensen-Dalsgaard, J.; Cunha, M. S.; Dall, T.; Frandsen, S.;
Karoff, C.; Monteiro, M. J. P. F. G.; Pijpers, F. P.
2009A&A...494..237T Altcode: 2008arXiv0811.3989T
We used HARPS to measure oscillations in the low-mass star τ
Cet. Although the data were compromised by instrumental noise, we have
been able to extract the main features of the oscillations. We found τ
Cet to oscillate with an amplitude that is about half that of the Sun,
and with a mode lifetime that is slightly shorter than solar. The large
frequency separation is 169 μHz, and we have identified modes with
degrees 0, 1, 2, and 3. We used the frequencies to estimate the mean
density of the star to an accuracy of 0.45% which, combined with the
interferometric radius, gives a mass of 0.783 ± 0.012 M<SUB>⊙</SUB>
(1.6%). <P />Based on observations collected at the European Southern
Observatory, La Silla, Chile (ESO Programme 74.D-0380).
---------------------------------------------------------
Title: On the opacity change required to compensate for the revised
solar composition
Authors: Christensen-Dalsgaard, J.; di Mauro, M. P.; Houdek, G.;
Pijpers, F.
2009A&A...494..205C Altcode: 2008arXiv0811.1001C
Context: Recent revisions of the determination of the solar composition
have resulted in solar models in marked disagreement with helioseismic
inferences. <BR />Aims: The effect of the inferred composition change
on the models is largely caused by the change in opacity. Thus, we
wish to determine an intrinsic opacity change that would compensate
for the revision to the composition. <BR />Methods: By comparing models
computed with the old and revised compositions we determine the required
opacity change. Models are computed with the opacity modified in this
manner and used as reference in helioseismic inversions to determine
the difference between the solar and model sound speed. <BR />Results:
An opacity increase ranging between around 30 per cent close to the base
of the convection zone and a few percent in the solar core leads to a
sound-speed profile, for the revised composition, that is essentially
indistinguishable from the original solar model. As a function of the
logarithm of temperature this is well represented by a simple cubic
fit. The physical realism of such a change remains debatable, however.
---------------------------------------------------------
Title: Asteroseismology: The Next Frontier in Stellar Astrophysics
Authors: Giampapa, Mark S.; Aerts, Conny; Bedding, Tim; Bonanno,
Alfio; Brown, Timothy M.; Christensen-Dalsgaard, Jorgen; Dominik,
Martin; Ge, Jian; Gilliland, Ronald L.; Harvey, J. W.; Hill, Frank;
Kawaler, Steven D.; Kjeldsen, Hans; Kurtz, D. W.; Marcy, Geoffrey W.;
Matthews, Jaymie M.; Monteiro, Mario Joao P. F. G.; Schou, Jesper
2009astro2010S..91G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Division V: Vaviable Stars
Authors: Giménez, Alvaro; Kawaler, Steven D.; Aerts, Conny;
Christensen-Dalsgaard, Jørgen; Breger, Michael; Guinan, Edward F.;
Kurtz, Donald W.; Rucinski, Slavek M.
2009IAUTA..27..251G Altcode:
Division V deals with all aspects of stellar variability, either
intrinsic or due to eclipses by its companion in a binary system. In
the case of intrinsic stellar variability the analysis of pulsating
stars, surface inhomogeneities, stellar activity and oscillations
are considered. For close binaries, classical detached eclipsing
binaries are studied as well as more interacting systems, like contact
and semi-detached binaries, or those with compact components, like
cataclysmic variables and X-ray binaries, including the physics of
accretion processes.
---------------------------------------------------------
Title: Dynamos and magnetic fields of the Sun and other cool stars,
and their role in the formation and evolution of stars and in the
habitability of planets
Authors: Schrijver, Karel; Carpenter, Ken; Karovska, Margarita; Ayres,
Tom; Basri, Gibor; Brown, Benjamin; Christensen-Dalsgaard, Joergen;
Dupree, Andrea; Guinan, Ed; Jardine, Moira; Miesch, Mark; Pevtsov,
Alexei; Rempel, Matthias; Scherrer, Phil; Solanki, Sami; Strassmeier,
Klaus; Walter, Fred
2009astro2010S.262S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Commission 12: Solar Radiation and Structure
Authors: Martínez Pillet, Valentin; Kosovichev, Alexander;
Mariska, John T.; Bogdan, Thomas J.; Asplund, Martin; Cauzzi, Gianna;
Christensen-Dalsgaard, Jørgen; Cram, Lawrence E.; Gan, Weiqun; Gizon,
Laurent; Heinzl, Petr; Rovira, Marta G.; Venkatakrishnan, P.
2009IAUTA..27..104M Altcode:
Commission 12 encompasses investigations on the internal structure
and dynamics of the Sun, mostly accessible through the techniques of
local and global helioseismology, the quiet solar atmosphere, solar
radiation and its variability, and the nature of relatively stable
magnetic structures like sunspots, faculae and the magnetic network. A
revision of the progress made in these fields is presented. For some
specific topics, the review has counted with the help of experts
outside the Commission Organizing Committee that are leading and/or
have recently presented relevant works in the respective fields. In
this cases the contributor's name is given in parenthesis.
---------------------------------------------------------
Title: Kepler
Authors: Christensen-Dalsgaard, J.; Arentoft, T.; Brown, T. M.;
Gilliland, R. L.; Kjeldsen, H.; Borucki, W. J.; Koch, D.
2008CoAst.157..266C Altcode:
Kepler is a NASA mission, scheduled for launch in April 2009, whose
principal purpose is to investigate extra-solar planetary systems,
through the detection of planetary transits across their parent
star. An important goal is to determine the prevalence of Earth-size
planets in Earth-like orbits. The required photometric precision also
makes the mission very well- suited for asteroseismology, with the
important purpose of characterizing the central stars in planetary
systems. An extensive asteroseismic programme is planned for Kepler,
organized in an international collaboration in the Kepler Asteroseismic
Science Consortium.
---------------------------------------------------------
Title: Dipole modes of stellar oscillations
Authors: Dogan, G.; Christensen-Dalsgaard, J.; Takata, M.
2008CoAst.157..301D Altcode:
We focus on dipole mode stellar oscillations (with l=1) which have
been a challenge in identifying the modes. We make use of a new mode
identification scheme specific to these oscillations.
---------------------------------------------------------
Title: A Multisite Campaign to Measure Solar-like Oscillations in
Procyon. I. Observations, Data Reduction, and Slow Variations
Authors: Arentoft, Torben; Kjeldsen, Hans; Bedding, Timothy R.;
Bazot, Michaël; Christensen-Dalsgaard, Jørgen; Dall, Thomas H.;
Karoff, Christoffer; Carrier, Fabien; Eggenberger, Patrick; Sosnowska,
Danuta; Wittenmyer, Robert A.; Endl, Michael; Metcalfe, Travis S.;
Hekker, Saskia; Reffert, Sabine; Butler, R. Paul; Bruntt, Hans;
Kiss, László L.; O'Toole, Simon J.; Kambe, Eiji; Ando, Hiroyasu;
Izumiura, Hideyuki; Sato, Bun'ei; Hartmann, Michael; Hatzes, Artie;
Bouchy, Francois; Mosser, Benoit; Appourchaux, Thierry; Barban,
Caroline; Berthomieu, Gabrielle; Garcia, Rafael A.; Michel, Eric;
Provost, Janine; Turck-Chièze, Sylvaine; Martić, Milena; Lebrun,
Jean-Claude; Schmitt, Jerome; Bertaux, Jean-Loup; Bonanno, Alfio;
Benatti, Serena; Claudi, Riccardo U.; Cosentino, Rosario; Leccia,
Silvio; Frandsen, Søren; Brogaard, Karsten; Glowienka, Lars; Grundahl,
Frank; Stempels, Eric
2008ApJ...687.1180A Altcode: 2008arXiv0807.3794A
We have carried out a multisite campaign to measure oscillations in
the F5 star Procyon A. We obtained high-precision velocity observations
over more than three weeks with 11 telescopes, with almost continuous
coverage for the central 10 days. This represents the most extensive
campaign so far organized on any solar-type oscillator. We describe in
detail the methods we used for processing and combining the data. These
involved calculating weights for the velocity time series from the
measurement uncertainties and adjusting them in order to minimize the
noise level of the combined data. The time series of velocities for
Procyon shows the clear signature of oscillations, with a plateau of
excess power that is centered at 0.9 mHz and is broader than has been
seen for other stars. The mean amplitude of the radial modes is 38.1
+/- 1.3 cm s<SUP>-1</SUP> (2.0 times solar), which is consistent with
previous detections from the ground and by the WIRE spacecraft, and
also with the upper limit set by the MOST spacecraft. The variation
of the amplitude during the observing campaign allows us to estimate
the mode lifetime to be 1.5<SUP>+ 1.9</SUP><SUB>-0.8</SUB> days. We
also find a slow variation in the radial velocity of Procyon, with good
agreement between different telescopes. These variations are remarkably
similar to those seen in the Sun, and we interpret them as being due to
rotational modulation from active regions on the stellar surface. The
variations appear to have a period of about 10 days, which presumably
equals the stellar rotation period or, perhaps, half of it. The amount
of power in these slow variations indicates that the fractional area of
Procyon covered by active regions is slightly higher than for the Sun.
---------------------------------------------------------
Title: Stellar Oscillations Network Group SONG
Authors: Grundahl, F.; Arentoft, T.; Christensen-Dalsgaard, J.;
Frandsen, S.; Kjeldsen, H.; Rasmussen, P. K.
2008JPhCS.118a2041G Altcode: 2007arXiv0705.0851G
The Stellar Oscillations Network Group (SONG) is an initiative which
aims at designing and building a ground-based network of 1 m telescopes
dedicated to the study of phenomena occurring in the time domain. In
particular the study of stellar oscillations and the search for and
characterisation of extra-solar planets. There will be eight identical
nodes in the network, located at existing sites. Each node will have
two instruments: 1) a high-resolution spectrograph for obtaining high
precision radial velocities using an iodine cell as velocity reference
- this will be the main instrument for asteroseismology because
solar-like oscillations are much easier to detect in velocity than
intensity; and 2) an optical imager which will be used for photometry
and guiding. Detailed design of the network prototype node will begin
in 2008, and a fully functioning and tested prototype will be ready
by the end of 2011, with the goal of achieving a fully operational
network around 2014.
---------------------------------------------------------
Title: Oscillations in Procyon A: First results from a multi-site
campaign
Authors: Hekker, S.; Arentoft, T.; Kjeldsen, H.; Bedding, T. R.;
Christensen-Dalsgaard, J.; Reffert, S.; Bruntt, H.; Butler, R. P.;
Kiss, L. L.; O'Toole, S. J.; Kambe, E.; Ando, H.; Izumiura, H.;
Sato, B.; Hartmann, M.; Hatzes, A. P.; Appourchaux, T.; Barban, C.;
Berthomieu, G.; Bouchy, F.; García, R. A.; Lebrun, J. -C.; Martić,
M.; Michel, E.; Mosser, B.; Nghiem, P. A. P.; Provost, J.; Samadi,
R.; Thévenin, F.; Turck-Chièze, S.; Bonanno, S. A.; Benatti, S.;
Claudi, R. U.; Cosentino, R.; Leccia, S.; Frandsen, S.; Brogaard,
K.; Grundahl, F.; Stempels, H. C.; Bazot, M.; Dall, T. H.; Karoff,
C.; Carrier, F.; Eggenberger, P.; Sosnowska, D.; Wittenmyer, R. A.;
Endl, M.; Metcalfe, T. S.
2008JPhCS.118a2059H Altcode: 2007arXiv0710.3772H
Procyon A is a bright F5IV star in a binary system. Although the
distance, mass and angular diameter of this star are all known with high
precision, the exact evolutionary state is still unclear. Evolutionary
tracks with different ages and different mass fractions of hydrogen
in the core pass, within the errors, through the observed position of
Procyon A in the Hertzsprung-Russell diagram. For more than15 years
several different groups have studied the solar-like oscillations in
Procyon A to determine its evolutionary state. Although several studies
independently detected power excess in the periodogram, there is no
agreement on the actual oscillation frequencies yet. This is probably
due to either insufficient high-quality data (i.e., aliasing) or due
to intrinsic properties of the star (i.e., short mode lifetimes). Now
a spectroscopic multi-site campaign using 10 telescopes world-wide
(minimizing aliasing effects) with a total time span of nearly 4
weeks (increase the frequency resolution) is performed to identify
frequencies in this star and finally determine its properties and
evolutionary state.
---------------------------------------------------------
Title: Helio- and asteroseismology
Authors: Christensen-Dalsgaard, Jørgen
2008IAUS..252..135C Altcode:
Observations of solar and stellar oscillations are providing detailed
information about stellar interiors. In the case of the Sun the set
of observed frequencies is sufficiently detailed and accurate that
the properties of the solar interior, such as sound speed, density
and internal rotation, can be inferred with substantial precision
and resolution. This allows detailed tests of solar modelling, with
interesting and to some extent controversial results. Observations of
solar-like oscillations in distant stars have started only recently,
owing their very small amplitudes. However, developments in ground-based
equipment and observations from space are revolutionizing this field,
promising greatly increased insight into the structure and evolution
of the stars.
---------------------------------------------------------
Title: The Kepler asteroseismic investigation
Authors: Christensen-Dalsgaard, J.; Arentoft, T.; Brown, T. M.;
Gilliland, R. L.; Kjeldsen, H.; Borucki, W. J.; Koch, D.
2008JPhCS.118a2039C Altcode:
The NASA Kepler mission for studies of extra-solar planets, with
expected launch early in 2009, will provide a large set of excellent
data for asteroseismology. Here we provide a brief presentation of
the mission and discuss some aspects of the expected results of the
asteroseismic investigations and the organization of the effort in
the Kepler Asteroseismic Science Consortium (KASC).
---------------------------------------------------------
Title: SONG Stellar Observations Network Group
Authors: Grundahl, Frank; Christensen-Dalsgaard, J.; Kjeldsen, H.;
Frandsen, S.; Arentoft, T.; Kjaergaard, P.; Jørgensen, U. G.
2008IAUS..252..465G Altcode:
Several areas of stellar observations depend critically on nearly
continuous observations of individual objects over very extended
periods. Important examples are investigations of stellar oscillations
to carry out asteroseismology, and the search for extra-solar
planets. To meet this requirement we are establishing the SONG
network, consisting of 8 sites with a 1-meter-class telescope with
a suitable geographical distribution. These will be optimized for
asteroseismology based on Doppler-velocity observations and the
characterization of extra-solar planets with photometry, using
gravitational microlensing. Funding has been obtained towards the
construction of the prototype SONG telescope which will be set up on
Tenerife, with first light expected in 2011. The full network will be
established in parallel with the tests of the prototype and is planned
to be operational in 2014.
---------------------------------------------------------
Title: AsteroFLAG — from the Sun to the stars
Authors: Chaplin, W. J.; Appourchaux, T.; Arentoft, T.; Ballot, J.;
Baudin, F.; Bazot, M.; Bedding, T. R.; Christensen-Dalsgaard, J.;
Creevey, O. L.; Duez, V.; Elsworth, Y.; Fletcher, S. T.; García,
R. A.; Gough, D. O.; Jiménez, A.; Jiménez-Reyes, S. J.; Houdek, G.;
Kjeldsen, H.; Lazrek, M.; Leibacher, J. W.; Monteiro, M. J. P. F. G.;
Neiner, C.; New, R.; Régulo, C.; Salabert, D.; Samadi, R.; Sekii,
T.; Sousa, S. G.; Toutain, T.; Turck-Chièze, S.
2008JPhCS.118a2048C Altcode:
We stand on the threshold of a critical expansion of asteroseismology
of Sun-like stars, the study of stellar interiors by observation
and analysis of their global acoustic modes of oscillation. The
Sun-like oscillations give a very rich spectrum allowing the internal
structure and dynamics to be probed down into the stellar cores to
very high precision. Asteroseismic observations of many stars will
allow multiple-point tests of crucial aspects of stellar evolution
and dynamo theory. The aims of the asteroFLAG collaboration are to
help the community to refine existing, and to develop new, methods
for analysis of the asteroseismic data on the Sun-like oscillators.
---------------------------------------------------------
Title: The Current Status of Asteroseismology
Authors: Aerts, C.; Christensen-Dalsgaard, J.; Cunha, M.; Kurtz, D. W.
2008SoPh..251....3A Altcode: 2008arXiv0803.3527A; 2008SoPh..tmp...80A
Stellar evolution, a fundamental bedrock of modern astrophysics,
is driven by the physical processes in stellar interiors. While we
understand these processes in general terms, we lack some important
ingredients. Seemingly small uncertainties in the input physics of the
models (e.g., the opacities or the amount of mixing and of interior
rotation) have large consequences for the evolution of stars. The goal
of asteroseismology is to improve the description of the interior
physics of stars by means of their oscillations, just as global
helioseismology led to a huge step forward in our knowledge about the
internal structure of the Sun. In this paper we present the current
status of asteroseismology by considering case studies of stars with a
variety of masses and evolutionary stages. In particular, we outline
how the confrontation between the observed oscillation frequencies
and those predicted by the models allows us to pinpoint limitations
of the input physics of current models and improve them to a level
that cannot be reached with any other current method.
---------------------------------------------------------
Title: Asteroseismology-Studying stellar structure
Authors: Kjeldsen, Hans; Bedding, Timothy R.; Christensen-Dalsgaard,
Jørgen
2008AIPC.1043..365K Altcode:
Oscillations occur in stars of most masses and essentially all stages
of evolution. We discuss briefly the potential of asteroseismology,
i.e., the study of the frequencies and other properties of stellar
oscillations with the aim of extracting fundamental parameters such
as density, mass, radius, age and rotation period. We also describe
the Kepler Asteroseismic Investigation-the use of asteroseismology on
the NASA Kepler mission to study stellar structure and evolution and
provide information on the accuracy of the frequency measurements that
can be obtained by the NASA Kepler mission. The Kepler mission will
provide a comprehensive overview of stellar properties across a large
part of the HR diagram, including information about the excitation
and damping of the modes, and detailed information about the internal
structure of a substantial number of stars.
---------------------------------------------------------
Title: Correcting Stellar Oscillation Frequencies for Near-Surface
Effects
Authors: Kjeldsen, Hans; Bedding, Timothy R.; Christensen-Dalsgaard,
Jørgen
2008ApJ...683L.175K Altcode: 2008arXiv0807.1769K
In helioseismology, there is a well-known offset between observed
and computed oscillation frequencies. This offset is known to
arise from improper modeling of the near-surface layers of the Sun,
and a similar effect must occur for models of other stars. Such an
effect impedes progress in asteroseismology, which involves comparing
observed oscillation frequencies with those calculated from theoretical
models. Here, we use data for the Sun to derive an empirical correction
for the near-surface offset, which we then apply to three other stars
(α Cen A, α Cen B, and β Hyi). The method appears to give good
results, in particular providing an accurate estimate of the mean
density of each star.
---------------------------------------------------------
Title: ADIPLS—the Aarhus adiabatic oscillation package
Authors: Christensen-Dalsgaard, Jørgen
2008Ap&SS.316..113C Altcode: 2008Ap&SS.tmp....1C; 2007arXiv0710.3106C
Development of the Aarhus adiabatic pulsation code started around
1978. Although the main features have been stable for more than a
decade, development of the code is continuing, concerning numerical
properties and output. The code has been provided as a generally
available package and has seen substantial use at a number of
installations. Further development of the package, including bringing
the documentation closer to being up to date, is planned as part of
the HELAS Coordination Action.
---------------------------------------------------------
Title: ASTEC—the Aarhus STellar Evolution Code
Authors: Christensen-Dalsgaard, Jørgen
2008Ap&SS.316...13C Altcode: 2007Ap&SS.tmp..461C; 2007arXiv0710.3114C
The Aarhus code is the result of a long development, starting in
1974, and still ongoing. A novel feature is the integration of the
computation of adiabatic oscillations for specified models as part of
the code. It offers substantial flexibility in terms of microphysics and
has been carefully tested for the computation of solar models. However,
considerable development is still required in the treatment of nuclear
reactions, diffusion and convective mixing.
---------------------------------------------------------
Title: CoRoT/ESTA TASK 1 and TASK 3 comparison of the internal
structure and seismic properties of representative stellar
models. Comparisons between the ASTEC, CESAM, CLES, GARSTEC and
STAROX codes
Authors: Lebreton, Yveline; Montalbán, Josefina;
Christensen-Dalsgaard, Jørgen; Roxburgh, Ian W.; Weiss, Achim
2008Ap&SS.316..187L Altcode: 2008arXiv0801.0928L; 2008Ap&SS.tmp...39L
We compare stellar models produced by different stellar evolution
codes for the CoRoT/ESTA project, comparing their global quantities,
their physical structure, and their oscillation properties. We discuss
the differences between models and identify the underlying reasons
for these differences. The stellar models are representative of
potential CoRoT targets. Overall we find very good agreement between
the five different codes, but with some significant deviations. We find
noticeable discrepancies (though still at the per cent level) that
result from the handling of the equation of state, of the opacities
and of the convective boundaries. The results of our work will be
helpful in interpreting future asteroseismology results from CoRoT.
---------------------------------------------------------
Title: The CoRoT evolution and seismic tools activity. Goals and tasks
Authors: Lebreton, Y.; Monteiro, M. J. P. F. G.; Montalbán, J.;
Moya, A.; Baglin, A.; Christensen-Dalsgaard, J.; Goupil, M. -J.;
Michel, E.; Provost, J.; Roxburgh, I. W.; Scuflaire, R.; ESTA Team
2008Ap&SS.316....1L Altcode: 2008arXiv0805.0977L; 2008Ap&SS.tmp..157L
The forthcoming data expected from space missions such as CoRoT
require the capacity of the available tools to provide accurate models
whose numerical precision is well above the expected observational
errors. In order to secure that these tools meet the specifications,
a team has been established to test and, when necessary, to improve
the codes available in the community. The CoRoT Evolution and Seismic
Tool Activity (ESTA) has been set up with this mission. Several groups
have been involved. The present paper describes the motivation and the
organisation of this activity, providing the context and the basis for
the presentation of the results that have been achieved so far. This
is not a finished task as future even better data will continue to
demand more precise and complete tools for asteroseismology.
---------------------------------------------------------
Title: Inter-comparison of the g-, f- and p-modes calculated using
different oscillation codes for a given stellar model
Authors: Moya, A.; Christensen-Dalsgaard, J.; Charpinet, S.; Lebreton,
Y.; Miglio, A.; Montalbán, J.; Monteiro, M. J. P. F. G.; Provost,
J.; Roxburgh, I. W.; Scuflaire, R.; Suárez, J. C.; Suran, M.
2008Ap&SS.316..231M Altcode: 2007arXiv0711.2587M; 2008Ap&SS.tmp...49M
In order to make asteroseismology a powerful tool to explore stellar
interiors, different numerical codes should give the same oscillation
frequencies for the same input physics. Any differences found when
comparing the numerical values of the eigenfrequencies will be an
important piece of information regarding the numerical structure of the
code. The ESTA group was created to analyze the non-physical sources
of these differences. The work presented in this report is a part
of Task 2 of the ESTA group. Basically the work is devoted to test,
compare and, if needed, optimize the seismic codes used to calculate
the eigenfrequencies to be finally compared with observations. The
first step in this comparison is presented here. The oscillation
codes of nine research groups in the field have been used in this
study. The same physics has been imposed for all the codes in order to
isolate the non-physical dependence of any possible difference. Two
equilibrium models with different grids, 2172 and 4042 mesh points,
have been used, and the latter model includes an explicit modelling of
semiconvection just outside the convective core. Comparing the results
for these two models illustrates the effect of the number of mesh points
and their distribution in particularly critical parts of the model,
such as the steep composition gradient outside the convective core. A
comprehensive study of the frequency differences found for the different
codes is given as well. These differences are mainly due to the use of
different numerical integration schemes. The number of mesh points and
their distribution are crucial for interpreting the results. The use
of a second-order integration scheme plus a Richardson extrapolation
provides similar results to a fourth-order integration scheme. The
proper numerical description of the Brunt-Väisälä frequency in
the equilibrium model is also critical for some modes. This influence
depends on the set of the eigenfunctions used for the solution of the
differential equations. An unexpected result of this study is the high
sensitivity of the frequency differences to the inconsistent use of
values of the gravitational constant ( G) in the oscillation codes,
within the range of the experimentally determined ones, which differ
from the value used to compute the equilibrium model. This effect can
provide differences for a given equilibrium model substantially larger
than those resulting from the use of different codes or numerical
techniques; the actual differences between the values of G used by
the different codes account for much of the frequency differences
found here.
---------------------------------------------------------
Title: AsteroFLAG: First results from hare-and-hounds Exercise #1
Authors: Chaplin, W. J.; Appourchaux, T.; Arentoft, T.; Ballot, J.;
Christensen-Dalsgaard, J.; Creevey, O. L.; Elsworth, Y.; Fletcher,
S. T.; García, R. A.; Houdek, G.; Jiménez-Reyes, S. J.; Kjeldsen,
H.; New, R.; Régulo, C.; Salabert, D.; Sekii, T.; Sousa, S. G.;
Toutain, T.; rest of asteroFLAG Group
2008AN....329..549C Altcode: 2008arXiv0803.4143C
We report on initial results from the first phase of Exercise #1 of the
asteroFLAG hare and hounds. The asteroFLAG group is helping to prepare
for the asteroseismology component of NASA's Kepler mission, and the
first phase of Exercise #1 is concerned with testing extraction of
estimates of the large and small frequency spacings of the low-degree p
modes from Kepler-like artificial data. These seismic frequency spacings
will provide key input for complementing the exoplanet search data.
---------------------------------------------------------
Title: Finding Earth-size planets in the habitable zone: the Kepler
Mission
Authors: Borucki, William; Koch, David; Basri, Gibor; Batalha, Natalie;
Brown, Timothy; Caldwell, Douglas; Christensen-Dalsgaard, Jørgen;
Cochran, William; Dunham, Edward; Gautier, Thomas N.; Geary, John;
Gilliland, Ronald; Jenkins, Jon; Kondo, Yoji; Latham, David; Lissauer,
Jack J.; Monet, David
2008IAUS..249...17B Altcode: 2007IAUS..249...17B
The Kepler Mission is a space-based mission whose primary goal is
to detect Earth-size and smaller planets in the habitable zone of
solar-like stars. The mission will monitor more than 100,000 stars
for transits with a differential photometric precision of 20 ppm
at V=12 for a 6.5 hour transit. It will also provide asteroseismic
results on several thousand dwarf stars. It is specifically designed
to continuously observe a single field of view of greater than 100
square degrees for 3.5 or more years. <P />This overview describes the
mission design, its goals and capabilities, the measured performance
for those photometer components that have now been tested, the Kepler
Input Catalog, an overview of the analysis pipeline, the plans for the
Follow-up Observing Program to validate the detections and characterize
the parent stars, and finally, the plans for the Guest Observer and
Astrophysical Data Program.
---------------------------------------------------------
Title: Stellar Astrophysical Fluid Dynamics
Authors: Thompson, Michael J.; Christensen-Dalsgaard, Jørgen
2008safd.book.....T Altcode:
Preface; 1. A selective overview Jørgen Christensen-Dalsgaard and
Michael J. Thompson; Part I. Stellar Convection and Oscillations:
2. On the diversity of stellar pulsations Wojciech A. Dziembowski;
3. Acoustic radiation and mode excitation by turbulent convection
Günter Houdek; 4. Understanding roAp stars Margarida S. Cunha; 5. Waves
in the magnetised solar atmosphere Colin S. Rosenthal; Part II. Stellar
Rotation and Magnetic Fields: 6. Stellar rotation: a historical survey
Leon Mestel; 7. The oscillations of rapidly rotating stars Michel
Rieutord; 8. Solar tachocline dynamics: eddy viscosity, anti-friction,
or something in between? Michael E. McIntyre; 9. Dynamics of the solar
tachocline Pascale Garaud; 10. Dynamo processes: the interaction of
turbulence and magnetic fields Michael Proctor; 11. Dynamos in planets
Chris Jones; Part III. Physics and Structure of Stellar Interiors:
12. Solar constraints on the equation of state Werner Däppen;
13. 3He transport and the solar neutrino problem Chris Jordinson;
14. Mixing in stellar radiation zones Jean-Paul Zahn; 15. Element
settling and rotation-induced mixing in slowly rotating stars Sylvie
Vauclair; Part IV. Helio- and Asteroseismology: 16. Solar structure
and the neutrino problem Hiromoto Shibahashi; 17. Helioseismic data
analysis Jesper Schou; 18. Seismology of solar rotation Takashi Sekii;
19. Telechronohelioseismology Alexander Kosovichev; Part V. Large-Scale
Numerical Experiments: 20. Bridges between helioseismology and models
of convection zone dynamics Juri Toomre; 21. Numerical simulations of
the solar convection zone Julian R. Elliott; 22. Modelling solar and
stellar magnetoconvection Nigel Weiss; 23. Nonlinear magnetoconvection
in the presence of a strong oblique field Keith Julien, Edgar Knobloch
and Steven M. Tobias; 24. Simulations of astrophysical fluids Marcus
Brüggen; Part VI. Dynamics: 25. A magic electromagnetic field Donald
Lynden-Bell; 26. Continuum equations for stellar dynamics Edward
A. Spiegel and Jean-Luc Thiffeault; 27. Formation of planetary systems
Douglas N. C. Lin; 28. The solar-cycle global warming as inferred from
sky brightness variation Wasaburo Unno and Hiromoto Shibahashi.
---------------------------------------------------------
Title: Estimation of stellar parameters using Monte Carlo Markov
Chains
Authors: Bazot, M.; Bourguignon, S.; Christensen-Dalsgaard, J.
2008MmSAI..79..660B Altcode: 2008arXiv0803.2529B
We apply Monte Carlo Markov Chain methods to the stellar parameter
estimation problem. This technique is useful when dealing with
non-linear models and allows to derive realistic error bars on the
inferred parameters. We give the first results obtained for {alpha
Cen A}.
---------------------------------------------------------
Title: Kepler Mission: Current Status
Authors: Borucki, William J.; Koch, D. G.; Lissauer, J. J.; Bryson,
S.; Natalie, B.; Caldwell, D. A.; DeVore, E.; Jenkins, J. M.;
Christensen-Dalsgaard, J.; Cochran, W. D.; Dunham, E. W.; Gautier,
T. N.; Geary, J. C.; Latham, D. W.; Sasselov, D.; Gilliland, R. L.;
Gould, A.; Howell, S. B.; Monet, D. G.
2007AAS...211.3603B Altcode: 2007BAAS...39R.788B
Kepler is a Discovery-class mission designed to determine the frequency
of Earth-size planets in and near the habitable zone of solar-like
stars. The instrument consists of a high precision photometer with
Schmidt-type optics and a focal plane containing 95 million pixels
to monitor over 100,000 stars to search for patterns of transits
generated by planets as small as Mars. The recent reduction in the
mission duration is discussed with regard to the impact on the expected
science product and null statistics. Both terrestrial and giant planets
discoveries will be followed up with ground-based Doppler-velocity
observations to determine mass and density. <P />The first meeting of
Kepler Asteroseismic Science Consortium was held in Paris to organize
an international team to analyze the Kepler data to determine the
characteristics of the brighter target stars including their size
and age. Stellar size determinations accurate to a few percent are
expected. These will allow very accurate planet sizes to be determined
from the depth of the transit signals. <P />NASA HQ received thirty six
proposals for the Participating Scientist Program and chose several new
members to join the Science Team. <P />Both the 0.95 m Schmidt corrector
and 1.4 m aperture primary mirror have been completed and delivered for
integration into the photometer. The focal plane with forty-two science
CCD detectors and their processing electronics has been assembled and
tested. The spacecraft assembly has begun with the mounting of the
reaction control system, reaction wheels, attitude determination &
control system, and power systems. Both the photometer and spacecraft
are nearing final assembly with all subsystems having passed their
environmental and performance testing. The photometer to spacecraft
integration will begin this spring. The Mission is on schedule for
a launch in February 2009. <P />The Kepler Mission is funded by the
NASA Astrophysics Division, Science Mission Directorate.
---------------------------------------------------------
Title: Commission 27: Variable Stars
Authors: Aerts, Conny; Kawaler, Steven D.; Christensen-Dalsgaard,
Jørgen; Bedding, Timothy R.; Cacciari, Carla; Cottrell, Peter L.;
Cunha, Margarida; Handler, Gerald; Martinez, Peter; Sasselov, Dimitar
D.; Somasundaram, Seetha; Welch, Douglas L.
2007IAUTB..26..168A Altcode:
The meeting started at 16h00. The president welcomed the 24 participants
to the business meeting of Commission 27. After the approval of the
agenda, she gave an overview of the activities of Commission 27 of
the past three years.
---------------------------------------------------------
Title: Commission 35: Stellar Constitution
Authors: Dziembowski, Wojciech A.; D'Antona, Francesca; VandenBerg,
Don A.; Charbonnel, Corinne; Christensen-Dalsgaard, Joergen; Guzik,
Joyce A.; Langer, Norbert; Larson, Richard B.; Liebert, James W.;
Meynet, Georges; Müller, Ewald; Saio, Hideyuki
2007IAUTB..26..158D Altcode:
The session was brief and quite informal as there were only six
participants. The agenda included my report on organizational activities
of the Commission during the 2003-2006 term and Virginia Trimble's
presentation Presence of binary stars in the current astronomical
literature. I summarize below the most important part of my report.
---------------------------------------------------------
Title: Division v: Variable Stars
Authors: Christensen-Dalsgaard, Jørgen; Giménez, Alvaro; Guinan,
Edward F.; Aerts, Conny; Balona, Luis A.; Sahade, Jorge
2007IAUTB..26..165C Altcode:
Division V provides a joint forum for the study of stellar
variability in all its manifestations, whether due to pulsation,
surface inhomogeneities, evolutionary changes, or to eclipses and
other phenomena specifically related to double and multiple stars.
---------------------------------------------------------
Title: A spectroscopic search for non-radial pulsations in the δ
Scuti star γ Bootis
Authors: Ventura, R.; Catanzaro, G.; Christensen-Dalsgaard, J.;
di Mauro, M. P.; Paternò, L.
2007MNRAS.381.1647V Altcode: 2007arXiv0708.2364V; 2007MNRAS.tmp..890V
High-resolution spectroscopic observations of the rapidly
rotating δScuti star γBootis have been carried out in 2005,
over six consecutive nights, in order to search for line-profile
variability. Time-series, consisting of flux measurements at each
wavelength bin across the TiII 4571.917 Å line profile as a function
of time, have been Fourier analysed. <P />The results confirm the early
detection reported by Kennelly et al. of a dominant periodic component
at frequency 21.28 cycles d<SUP>-1</SUP> in the observer's frame,
probably due to a high-azimuthal-order sectorial mode. Moreover, we
found other periodicities at 5.06, 12.02cyclesd<SUP>-1</SUP>, probably
present but not secure, and at 11.70 and 18.09cyclesd<SUP>-1</SUP>,
uncertain. The latter frequency, if present, should be identifiable as
another high-azimuthal-order sectorial mode and the three additional
terms as low-l modes as proved by the analysis of the first three
moments of the line. Owing to the short time baseline and the one-site
temporal sampling we consider our results only preliminary but
encouraging for a more extensive multisite campaign. <P />A refinement
of the atmospheric physical parameters of the star has been obtained
from our spectroscopic data and adopted for preliminary computations
of evolutionary models of γBootis.
---------------------------------------------------------
Title: Asteroseismology and interferometry
Authors: Cunha, M. S.; Aerts, C.; Christensen-Dalsgaard, J.;
Baglin, A.; Bigot, L.; Brown, T. M.; Catala, C.; Creevey, O. L.;
Domiciano de Souza, A.; Eggenberger, P.; Garcia, P. J. V.; Grundahl,
F.; Kervella, P.; Kurtz, D. W.; Mathias, P.; Miglio, A.; Monteiro,
M. J. P. F. G.; Perrin, G.; Pijpers, F. P.; Pourbaix, D.; Quirrenbach,
A.; Rousselet-Perraut, K.; Teixeira, T. C.; Thévenin, F.; Thompson,
M. J.
2007A&ARv..14..217C Altcode: 2007arXiv0709.4613C
Asteroseismology provides us with a unique opportunity to improve
our understanding of stellar structure and evolution. Recent
developments, including the first systematic studies of solar-like
pulsators, have boosted the impact of this field of research within
astrophysics and have led to a significant increase in the size of
the research community. In the present paper we start by reviewing
the basic observational and theoretical properties of classical and
solar-like pulsators and present results from some of the most recent
and outstanding studies of these stars. We centre our review on those
classes of pulsators for which interferometric studies are expected
to provide a significant input. We discuss current limitations to
asteroseismic studies, including difficulties in mode identification
and in the accurate determination of global parameters of pulsating
stars, and, after a brief review of those aspects of interferometry
that are most relevant in this context, anticipate how interferometric
observations may contribute to overcome these limitations. Moreover,
we present results of recent pilot studies of pulsating stars involving
both asteroseismic and interferometric constraints and look into the
future, summarizing ongoing efforts concerning the development of
future instruments and satellite missions which are expected to have
an impact in this field of research.
---------------------------------------------------------
Title: γ Bootis: Asteroseismology with a 1-m Class Telescope
Authors: di Mauro, M. P.; Catanzaro, G.; Christensen-Dalsgaard, J.;
Paternò, L.; Ventimiglia, G.; Ventura, R.
2007AIPC..948..455D Altcode:
High-resolution spectroscopic observations carried out in 2005, allowed
Ventura et al. (2007) to identify oscillation modes on the rapidly
rotating δ Scuti star γ Bootis. Here we consider the theoretical
interpretation of the observed oscillation spectrum based on structure
models and oscillation frequencies calculated by including effects
due to the fast rotation.
---------------------------------------------------------
Title: Joint Discussion 17 Highlights of recent progress in the
seismology of the Sun and Sun-like stars
Authors: Bedding, Timothy R.; Brun, Allan S.; Christensen-Dalsgaard,
Jørgen; Crouch, Ashley; De Cat, Peter; García, Raphael A.; Gizon,
Laurent; Hill, Frank; Kjeldsen, Hans; Leibacher, John W.; Maillard,
Jean-Pierre; Mathis, S.; Rabello-Soares, M. Cristina; Rozelot,
Jean-Pierre; Rempel, Matthias; Roxburgh, Ian W.; Samadi, Réza; Talon,
Suzanne; Thompson, Michael J.
2007HiA....14..491B Altcode:
The seismology and physics of localized structures beneath the surface
of the Sun takes on a special significance with the completion in
2006 of a solar cycle of observations by the ground-based Global
Oscillation Network Group (GONG) and by the instruments on board the
Solar and Heliospheric Observatory (SOHO). Of course, the spatially
unresolved Birmingham Solar Oscillation Network (BiSON) has been
observing for even longer. At the same time, the testing of models of
stellar structure moves into high gear with the extension of deep probes
from the Sun to other solar-like stars and other multi-mode pulsators,
with ever-improving observations made from the ground, the success of
the MOST satellite, and the recently launched CoRoT satellite. Here
we report the current state of the two closely related and rapidly
developing fields of helio- and asteroseimology.
---------------------------------------------------------
Title: The Kepler Mission and Eclipsing Binaries
Authors: Koch, David; Borucki, William; Basri, Gibor; Brown, Timothy;
Caldwell, Douglas; Christensen-Dalsgaard, Jorgen; Cochran, William;
Devore, Edna; Dunham, Edward; Gautier, Thomas N.; Geary, John;
Gilliland, Ronald; Gould, Alan; Jenkins, Jon; Kondo, Yoji; Latham,
David; Lissauer, Jack; Monet, David
2007IAUS..240..236K Altcode: 2006IAUS..240E..21K
The Kepler Mission is a photometric mission with a precision of 14 ppm
( at R= 12) that is designed to continuously observe a single field of
view (FOV) of greater 100 sq deg in the Cygnus-Lyra region for four or
more years. The primary goal of the mission is to monitor >100,000
stars for transits of Earth-size and smaller planets in the habitable
zone of solar-like stars. In the process, many eclipsing binaries
(EB) will also be detected and light curves produced. To enhance and
optimize the mission results, the stellar characteristics for all
the stars in the FOV with R<16 will have been determined prior
to launch. As part of the verification process, stars with transit
candidates will have radial velocity follow-up observations performed to
determine the component masses and thereby separate eclipses caused by
stellar companions from transits caused by planets. The result will be
a rich database on EBs. The community will have access to the archive
for further analysis, such as, for EB modeling of the high-precision
light curves. A guest observer program is also planned to allow for
photometric observations of objects not on the target list but within
the FOV, since only the pixels of interest from those stars monitored
will be transmitted to the ground.
---------------------------------------------------------
Title: Solar-like Oscillations in the G2 Subgiant β Hydri from
Dual-Site Observations
Authors: Bedding, Timothy R.; Kjeldsen, Hans; Arentoft, Torben;
Bouchy, Francois; Brandbyge, Jacob; Brewer, Brendon J.; Butler,
R. Paul; Christensen-Dalsgaard, Jørgen; Dall, Thomas; Frandsen,
Søren; Karoff, Christoffer; Kiss, László L.; Monteiro, Mario
J. P. F. G.; Pijpers, Frank P.; Teixeira, Teresa C.; Tinney, C. G.;
Baldry, Ivan K.; Carrier, Fabien; O'Toole, Simon J.
2007ApJ...663.1315B Altcode: 2007astro.ph..3747B
We have observed oscillations in the nearby G2 subgiant star β
Hyi using high-precision velocity observations obtained over more
than a week with the HARPS and UCLES spectrographs. The oscillation
frequencies show a regular comb structure, as expected for solar-like
oscillations, but with several l=1 modes being strongly affected
by avoided crossings. These data, combined with those we obtained
five years earlier, allow us to identify 28 oscillation modes. By
scaling the large-frequency separation from the Sun, we measure the
mean density of β Hyi to an accuracy of 0.6%. The amplitudes of the
oscillations are about 2.5 times solar and the mode lifetime is 2.3
days. A detailed comparison of the mixed l=1 modes with theoretical
models should allow a precise estimate of the age of the star.
---------------------------------------------------------
Title: KEPLER Mission Status
Authors: Borucki, W. J.; Koch, D. G.; Lissauer, J.; Basri, G.;
Brown, T.; Caldwell, D. A.; Jenkins, J. M.; Caldwell, J. J.;
Christensen-Dalsgaard, J.; Cochran, W. D.; Dunham, E. W.; Gautier,
T. N.; Geary, J. C.; Latham, D.; Sasselov, D.; Gilliland, R. L.;
Howell, S.; Monet, D. G.; Batalha, N.
2007ASPC..366..309B Altcode:
Kepler is a Discovery-class mission designed to determine the frequency
of Earth-size and smaller planets in and near the habitable zone
(HZ) of dwarf stars. The instrument consists of a 0.95-m aperture
photometer capable of doing high precision photometry of more than
100,000 late-type main sequence stars to search for patterns of
transits. Multi-band ground-based observation of over 2 million stars
is currently underway to estimate the stellar parameters and to choose
appropriate targets. The association of planet size and occurrence
frequency with stellar mass and metallicity will be investigated. At
the end of the four year mission, several hundred terrestrial planets
(i.e., planets up to twice the diameter of the Earth) should be
discovered with periods between one day and 400 days if such planets
are common. As many as 100 Earth-size planets in the HZ could be
discovered. A null result would imply that terrestrial planets are
rare. The scientific community is invited to participate through the
"Participating Scientist", "Guest Observer' and Data Analysis programs.
---------------------------------------------------------
Title: Stellar Oscillations Network Group
Authors: Grundahl, F.; Kjeldsen, H.; Christensen-Dalsgaard, J.;
Arentoft, T.; Frandsen, S.
2007CoAst.150..300G Altcode:
Stellar Oscillations Network Group (SONG) is an initiative aimed at
designing and building a network of 1m-class telescopes dedicated
to asteroseismology and planet hunting. SONG will have 8 identical
telescope nodes each equipped with a high-resolution spectrograph
and an iodine cell for obtaining precision radial velocities and a
CCD camera for guiding and imaging purposes. The main asteroseismology
targets for the network are the brightest (V < 6) stars. In order to
improve performance and reduce maintenance costs the instrumentation
will only have very few modes of operation. In this contribution we
describe the motivations for establishing a network, the basic outline
of SONG and the expected performance.
---------------------------------------------------------
Title: Asteroseismology with the Kepler mission
Authors: Christensen-Dalsgaard, J.; Arentoft, T.; Brown, T. M.;
Gilliland, R. L.; Kjeldsen, H.; Borucki, W. J.; Koch, D.
2007CoAst.150..350C Altcode: 2007astro.ph..1323C
NASA's Kepler mission will fly a photometer based on a wide-field
Schmidt camera with a 0.95 m aperture, staring at a single field
continuously for at least 4 years. Although the mission's principal
aim is to locate transiting extrasolar planets, it will provide an
unprecedented opportunity to make asteroseismic observations on a
wide variety of stars. Plans are now being developed to exploit this
opportunity to the fullest.
---------------------------------------------------------
Title: A theoretical scenario for PMS δ Scuti stars
Authors: Ruoppo, A.; Marconi, M.; Marques, M.; Monteiro,
M. J. P. F. G.; Christensen-Dalsgaard, J.; Palla, F.; Ripepi, V.
2007CoAst.150...73R Altcode:
Nonradial pulsation models have been computed by means of the Aarhus
adiabatic code along an extensive set of CESAM PMS evolutionary
tracks. A theoretical tool for the interpretation of observed
periodicities is proposed.
---------------------------------------------------------
Title: Solar Cycle Changes Over 11 Years of Medium-Degree Helioseismic
Observations
Authors: Howe, Rachel; Komm, R. W.; Hill, F.; Christensen-Dalsgaard,
J.; Schou, J.; Thompson, M. J.
2007AAS...210.2218H Altcode: 2007BAAS...39..127H
The Global Oscillations Network Group (GONG) has now completed, and
the Michelson Doppler Imager (MDI) aboard SOHO will soon complete,
a full eleven years of continuous observations of the medium-degree
solar oscillations. This enables us to follow changes in the acoustic
mode parameters and interior dynamics over a full solar cycle. We
present results from observations of convection-zone dynamics, in
which the torsional oscillation pattern seen at the surface can be
followed throughout most of the bulk of the convection zone, and also
changes in the frequency, lifetime and amplitude of the modes which
can be shown to be closely related in space and time to the migrating
pattern of surface activity. <P />This work utilizes data obtained by
the Global Oscillation Network Group (GONG) program, managed by the
National Solar Observatory, which is operated by AURA, Inc. under a
cooperative agreement with the National Science Foundation. SOHO is
a mission of international cooperation between ESA and NASA.
---------------------------------------------------------
Title: Opportunities to Participate in the Kepler Mission
Authors: Borucki, William J.; Koch, D. G.; Lissauer, J. J.; Batalha,
N.; Caldwell, D. A.; DeVore, E.; Jenkins, J. M.; Christensen-Dalsgaard,
J.; Cochran, W. D.; Dunham, E. T.; Gautier, T. N.; Geary, J. C.;
Gilliland, R. L.; Gould, A.; Howell, S. B.; Monet, D. G.; Sasselov, D.
2007AAS...21011007B Altcode: 2007BAAS...39..235B
Several opportunities to participate in the Kepler Mission are
available; Participating Scientist Program (PSP), Guest Observer (GO)
Program, and Astrophysical Data Analysis Program (ADAP). <P />For the PS
option, investigators from the science community will propose programs
that complement those developed by the PI and Co-Investigators. The
proposed programs can be analytical, observational, or theoretical
in nature. Examples include: modeling eclipsing binary systems to
determine the characteristics of the stars and planets, measuring
and modeling timing variations in the epoch of transits to detect
non-transiting planets, characterizing the atmospheres of giant planets
detected from transits or from reflected light, and confirmation
of transits. The solicitation for the PSP is now open. <P />The
GO program will accommodate those investigators who wish to make
astrophysical measurements of the many different types of objects in
the Kepler FOV. Generally, these targets will differ from those chosen
for the transit search. Examples include variable stars of all types,
distribution and time variation of zodiacal light, and extragalactic
objects. It is expected that a total of about 3000 additional targets at
any one time will be available and that these selections can be changed
at intervals of 3 months. Most of the targets will be observed at a
cadence of once per 30 minutes, but a small subset can be observed with
a one minute cadence. All targets must be within the active area of the
Kepler FOV. The FOV will not be moved to accommodate a GO request. <P
/>Investigators desiring to analyze data from targets already on the
Kepler target list should apply to the ADAP. It will be an opportunity
to perform data mining on the existing database. <P />Acknowlegement:
This is funded by the Discovery Program Office, SMD.
---------------------------------------------------------
Title: Rotation of the solar convection zone from helioseismology
Authors: Christensen-Dalsgaard, Jørgen
2007IAUS..239..393C Altcode: 2006astro.ph.10942C
Helioseismology has provided very detailed inferences about rotation of
the solar interior. Within the convection zone the rotation rate roughly
shares the latitudinal variation seen in the surface differential
rotation. The transition to the nearly uniformly rotating radiative
interior takes place in a narrow tachocline, which is likely important
to the operation of the solar magnetic cycle.The convection-zone
rotation displays zonal flows, regions of slightly more rapid and
slow rotation, extending over much of the depth of the convection zone
and converging towards the equator as the solar cycle progresses. In
addition, there is some evidence for a quasi-periodic variation in
rotation, with a period of around 1.3 yr, at the equator near the
bottom of the convection zone.
---------------------------------------------------------
Title: A theoretical approach for the interpretation of pulsating
PMS intermediate-mass stars
Authors: Ruoppo, A.; Marconi, M.; Marques, J. P.; Monteiro,
M. J. P. F. G.; Christensen-Dalsgaard, J.; Palla, F.; Ripepi, V.
2007A&A...466..261R Altcode: 2007astro.ph..2110R
Context: The investigation of the pulsation properties of
pre-main-sequence intermediate-mass stars is a promising tool to
evaluate the intrinsic properties of these stars and to constrain
current evolutionary models. Many new candidates of this class
have been discovered during the last decade and very accurate data
are expected from space observations obtained for example with the
CoRoT satellite. <BR />Aims: In this context we aim at developing a
theoretical approach for the interpretation of observed frequencies,
both from the already available ground-based observations and from
the future more accurate and extensive CoRoT results. <BR />Methods:
To this purpose we have started a project devoted to the computations
of fine and extensive grids of asteroseismic models of intermediate
mass pre-main-sequence stars. The obtained frequencies are used to
derive an analytical relation between the large frequency separation
and the stellar luminosity and effective temperature and to develop a
tool to compare theory and observations in the echelle diagram. <BR
/>Results: The predictive capabilities of the proposed method are
verified through the application to two test stars. As a second step,
we apply the procedure to two true observations from multisite campaigns
and we are able to constrain their stellar parameters, in particular the
mass, in spite of the small number of frequencies. <BR />Conclusions:
We expect that with a significantly higher number of frequencies both
the stellar mass and age could be constrained and, at the same time,
the physics of the models could be tested.
---------------------------------------------------------
Title: Commission C27: Variable Stars
Authors: Aerts, Conny; Kawaler, Steven; Bedding, Tim; Cacciari, Carla;
Christensen-Dalsgaard, Jørgen; Cottrell, Peter; Cunha, Margarida;
Handler, Gerald; Martinez, Peter; Sasselov, Dimitar; Seetha, S.;
Welch, Doug
2007IAUTA..26..247A Altcode:
We report the major highlights of variable star research within the
past three years. This overview is limited to intrinsically variable
stars, because the achievements in variable star research stemming
from binarity, or multiplicity in general, is covered by the summary
report of Commissions 26 and 42.
---------------------------------------------------------
Title: Division V: Variable Stars
Authors: Christensen-Dalsgaard, Jørgen; Aerts, Conny; Giménez,
Alvaro; Guinan, Edward F.; Balona, Luis A.; Sahade, Jorge
2007IAUTA..26..245C Altcode:
Division V, "Variable Stars", consists of Commission 27, also called
"Variable Stars" and Commission 42, "Close Binaries". Thus the former
deals with stars whose variations are intrinsic, whereas in the latter
the variations are caused by the interactions between the components
in the binary. It is evident that the definition of the Division is
predominantly observational, and there may be cases where the assignment
of an object to one of the two commissions might be in doubt (a recent
somewhat related example was the first detection of an extra-solar
planet, in 54 Pegasi, where intrinsic variability of the star in the
form of high-order g modes was also initially suspected).
---------------------------------------------------------
Title: Commission 12: Solar Radiation & Structure
Authors: Bogdan, Thomas. J.; Martínez Pillet, Valentin; Asplund,
M.; Christensen-Dalsgaard, J.; Cauzzi, G.; Cram, L. E.; Dravins, D.;
Gan, W.; Henzl, P.; Kosovichev, A.; Mariska, J. T.; Rovira, M. G.;
Venkatakrishnan, P.
2007IAUTA..26...89B Altcode:
Commission 12 covers research on the internal structure and dynamics
of the Sun, the "quiet" solar atmosphere, solar radiation and its
variability, and the nature of relatively stable magnetic structures
like sunspots, faculae and the magnetic network. There is considerable
productive overlap with the other Commissions of Division II as
investigations move progressively toward the fertile intellectual
boundaries between traditional research disciplines. In large part,
the solar magnetic field provides the linkage that connects these
diverse themes. The same magnetic field that produces the more subtle
variations of solar structure and radiative output over the 11 yr
activity cycle is also implicated in rapid and often violent phenomena
such as flares, coronal mass ejections, prominence eruptions, and
episodes of sporadic magnetic reconnection.The last three years have
again brought significant progress in nearly all the research endeavors
touched upon by the interests of Commission 12. The underlying causes
for this success remain the same: sustained advances in computing
capabilities coupled with diverse observations with increasing levels
of spatial, temporal and spectral resolution. It is all but impossible
to deal with these many advances here in anything except a cursory and
selective fashion. Thankfully, the Living Reviews in Solar Physics; has
published several extensive reviews over the last two years that deal
explicitly with issues relevant to the purview of Commission 12. The
reader who is eager for a deeper and more complete understanding of
some of these advances is directed to http://www.livingreviews.org
for access to these articles.
---------------------------------------------------------
Title: Commission 35: Stellar Constitution
Authors: Dziembowski, Wojciech A.; D'Antona, Francesca; Charbonnel,
C.; Christensen-Dalsgaard, J.; Guzik, J.; Langer, N.; Larson, R.;
Liebert, J.; Meynet, G.; Müller, E.; Saio, H.; Vandenberg, D.
2007IAUTA..26..205D Altcode:
Ihe triennial report from Commission 35 covers its organizational
activities and highlights accomplishments in various topics of stellar
interior physics.
---------------------------------------------------------
Title: Diffusion and Helioseismology
Authors: Christensen-Dalsgaard, J.; Di Mauro, M. Pia
2007EAS....26....3C Altcode:
Helioseismic inferences have demonstrated very clearly the importance
of including element diffusion and settling in solar modelling:
models incorporating these processes are in substantially better
agreement with the inferred solar sound speed than are models that
neglect them. The remaining discrepancy between the models and the
Sun has been taken as evidence for mixing in the region just beneath
the convection zone. However, rather more serious discrepancies have
resulted from a revision of solar abundances, and no obvious solution
to this problem has been found so far. This perhaps demonstrates
the danger of complacency when dealing with so complex a thing as a
star. Hydrodynamical instabilities are likely to play a more important
role than acknowledged in standard stellar modelling. An interesting
example, if not relevant to modelling up to the present solar age,
is the possible onset of semiconvective instability just beneath the
convection zone, as first emphasized by Bahcall et al. (2001).
---------------------------------------------------------
Title: Microscopic Diffusion in Stellar Evolution Codes: First
Comparisons Results of ESTA-Task 3
Authors: Lebreton, Y.; Montalbán, J.; Christensen-Dalsgaard, J.;
Théado, S.; Hui-Bon-Hoa, A.; Monteiro, M. J. P. F. G.; Degl'Innocenti,
S.; Marconi, M.; Morel, P.; Prada Moroni, P. G.; Weiss, A.
2007EAS....26..155L Altcode: 2007astro.ph..3426L
We present recent work undertaken by the Evolution and Seismic Tools
Activity (ESTA) team of the CoRoT Seismology Working Group. The
new ESTA-Task 3 aims at testing, comparing and optimising stellar
evolution codes which include microscopic diffusion of the chemical
elements resulting from pressure, temperature and concentration
gradients. The results already obtained are globally satisfactory,
but some differences between the different numerical tools appear that
require further investigations.
---------------------------------------------------------
Title: Observational results and issues concerning the tachocline
Authors: Christensen-Dalsgaard, Jørgen; Thompson, Michael J.
2007sota.conf...53C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Temporal variations in solar rotation at the bottom of the
convection zone: The current status
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R.;
Schou, J.; Thompson, M. J.; Toomre, J.
2007AdSpR..40..915H Altcode:
We present the most recent results on the short-period variations
in the solar rotation rate near the base of the convection zone. The
1.3-year period which was reported in the early years of solar cycle 23
appears not to persist after 2001, but there are hints of fluctuations
at a different period during the declining phase of the cycle.
---------------------------------------------------------
Title: Comparisons for ESTA-Task3: ASTEC, CESAM and CLÉS
Authors: Christensen-Dalsgaard, J.
2007EAS....26..177C Altcode:
The ESTA activity under the CoRoT project aims at testing the tools
for computing stellar models and oscillation frequencies that will
be used in the analysis of asteroseismic data from CoRoT and other
large-scale upcoming asteroseismic projects. Here I report results of
comparisons between calculations using the Aarhus code (ASTEC) and
two other codes, for models that include diffusion and settling. It
is found that there are likely deficiencies, requiring further study,
in the ASTEC computation of models including convective cores.
---------------------------------------------------------
Title: Kepler Mission Development
Authors: Borucki, William J.; Koch, D.; Batalha, N.; Brown, T.;
Caldwell, D.; Christensen-Dalsgaard, J.; Dunham, E.; Gautier, T.;
Geary, J.; Gilliland, R.; Jenkins, J.; Latham, D.; Monet, D.
2006AAS...20912406B Altcode: 2006BAAS...38.1071B
Kepler is a Discovery-class mission designed to determine the frequency
of Earth-size and smaller planets in and near the habitable zone
of cool dwarf stars. The instrument is a wide field-of-view (FOV)
differential photometer with a 100 square degree FOV that continuously
and simultaneously monitors the brightness of more than 100,000
main-sequence stars with sufficient precision to detect transits by
Earth-size planets. <P />As part of the Kepler Mission, a ground-based
observation program is underway to measure the effective temperature,
log(g), metallicity, and size of 10<SUP>7</SUP> stars in the FOV
brighter than 19<SUP>th</SUP> magnitude. The resulting catalog allows
the Kepler Mission to choose well-characterized late-type dwarfs and
to exclude giants and early spectral types from the target list. The
catalog will be the most comprehensive study of stars in this portion
of our galaxy. An asteroseismic study of several thousand bright stars
will also be conducted. It is expected to yield detailed information
about the size, mass, and age of these stars. <P />In October, an
intensive, 5-day Critical Design Review of the mission was conducted by
two review teams. The teams’ findings are being used to refine the
mission development as assembly and testing of the flight components
progress. Development is on schedule for a launch on November 1,
2008. <P />In preparation for the launch, Participating Scientist and
Guest Observer Programs are being developed. The first is expected to
be announced in early 2007 while the latter is expected in 2008. The
Participating Scientist Program will call for interested members of
the science community to propose research programs that complement
and enhance those of the Kepler Science Team. The following year,
the Guest Observer Program will entertain astrophysical research on
any of type of target in the Kepler FOV.
---------------------------------------------------------
Title: Report on the CoRoT Evolution and Seismic Tools Activity
Authors: Monteiro, M. J. P. F. G.; Lebreton, Y.; Montalban, J.;
Christensen-Dalsgaard, J.; Castro, M.; Degl'Innocenti, S.; Moya, A.;
Roxburgh, I. W.; Scuflaire, R.; Baglin, A.; Cunha, M. S.; Eggenberger,
P.; Fernandes, J.; Goupil, M. J.; Hui-Bon-Hoa, A.; Marconi, M.;
Marques, J. P.; Michel, E.; Miglio, A.; Morel, P.; Pichon, B.; Prada
Moroni, P. G.; Provost, J.; Ruoppo, A.; Suarez, J. -C.; Suran, M.;
Teixeira, T. C.
2006ESASP1306..363M Altcode: 2006astro.ph..5685M
We present the work undertaken by the Evolution and Seismic Tools
Activity (ESTA) team of the CoRoT Seismology Working Group. We have
focused on two main tasks: Task 1 now finished has aimed at testing,
comparing and optimising seven stellar evolution codes which will
be used to model the internal structure and evolution of the CoRoT
target stars. Task 2, still underway, aims at testing, comparing and
optimising different seismic codes used to calculate the oscillations
of models for different types of stars. The results already obtained
are quite satisfactory, showing minor differences between the different
numerical tools provided the same assumptions on the physical parameters
are made. This work gives us confidence on the numerical tools that
will be available to interpret the future CoRoT seismic data.
---------------------------------------------------------
Title: The DynaMICS perspective
Authors: Turck-Chièze, S.; Schmutz, W.; Thuillier, G.; Jefferies,
S.; Pallé; Dewitt, S.; Ballot, J.; Berthomieu, G.; Bonanno, A.;
Brun, A. S.; Christensen-Dalsgaard, J.; Corbard, T.; Couvidat, S.;
Darwich, A. M.; Dintrans, B.; Domingo, V.; Finsterle, W.; Fossat,
E.; Garcia, R. A.; Gelly, B.; Gough, D.; Guzik, J.; Jiménez, A. J.;
Jiménez-Reyes, S.; Kosovichev, A.; Lambert, P.; Lefebvre, S.; Lopes,
I.; Martic, M.; Mathis, S.; Mathur, S.; Nghiem, P. A. P.; Piau, L.;
Provost, J.; Rieutord, M.; Robillot, J. M.; Rogers, T.; Roudier, T.;
Roxburgh, I.; Rozelot, J. P.; Straka, C.; Talon, S.; Théado, S.;
Thompson, M.; Vauclair, S.; Zahn, J. P.
2006ESASP.624E..24T Altcode: 2006soho...18E..24T
No abstract at ADS
---------------------------------------------------------
Title: European helio- and asteroseismology network HELAS
Authors: Roth, M.; Luhe, O. v. d.; Palle, P.; Thompson, M. J.;
Christensen-Dalsgaard, J.; Monteiro, M. J. P. F. G.; Gizon, L.;
Di Mauro, M. P.; Aerts, C.; Daszynska-Daszkiewicz, J.; Corbard, T.
2006ESASP.624E.130R Altcode: 2006soho...18E.130R
The Helio- and Asteroseismology Network (HELAS) is a Coordinated
Action funded by the FP6-Infrastructure-Programme of the European
Commission. Currently, HELAS consists of ten members. The objective
of HELAS is to co-ordinate European activities in helio- and
asteroseismology. HELAS will transfer knowledge and data analysis
techniques, and will prepare the European research community for
important missions in the immediate future.
---------------------------------------------------------
Title: Solar Convection Zone Dynamics: How Sensitive Are Inversions
to Subtle Dynamo Features?
Authors: Howe, R.; Rempel, M.; Christensen-Dalsgaard, J.; Hill, F.;
Komm, R.; Larsen, R. M.; Schou, J.; Thompson, M. J.
2006ApJ...649.1155H Altcode:
The nearly 10 year span of medium-degree helioseismic data from the
Global Oscillation Network Group and the Michelson Doppler Imager has
allowed us to study the evolving flows in the solar convection zone
over most of solar cycle 23. Using two independent two-dimensional
rotation inversion techniques and extensive studies of the resolution
using artificial data from different assumed flow profiles, including
those generated from sample mean field dynamo models, we attempt to
assess the reality of certain features seen in the inferred rotation
profiles. Our results suggest that the findings from observations of
a substantial depth dependence of the phase of the zonal flow pattern
in the low latitudes, and the penetration of the flows deep into the
convection zone, are likely to be real rather than artifacts of the
inversion process.
---------------------------------------------------------
Title: Solar rotation and zonal flows from Mount Wilson 60 ft
tower data
Authors: Howe, R.; Bogart, R.; Christensen-Dalsgaard, J.; Rhodes,
E. J., Jr.; Rose, P.; Schou, J.
2006ESASP.624E..56H Altcode: 2006soho...18E..56H
No abstract at ADS
---------------------------------------------------------
Title: Prospects for helio- and asteroseismology
Authors: Christensen-Dalsgaard, J.
2006ESASP.624E..41C Altcode: 2006soho...18E..41C; 2006astro.ph.10614C
Major progress has been made in helio- and asteroseismology in
recent years. In helioseismology, much of the activity has been in
local helioseismology. However, the recent revision of solar surface
abundances, and the resulting problems in reconciling solar models
with the helioseismic inferences, have lead to renewed activity in
solar modelling and global helioseismology. Interesting, although
perhaps not compelling, evidence has been found for solar g modes in
observations with the GOLF instrument on the SOHO spacecraft. Extensive
asteroseismic results have been obtained from ground-based observations
as well as from the WIRE and MOST satellites, and much is expected
from the upcoming launch of the CoRoT satellite and, in a few years,
from the Kepler mission. In parallel, stellar modelling is being
extended to take some account of hydrodynamical effects, while
large-scale hydrodynamical calculations are providing increasingly
realistic simulations of these effects. The outcome of these activities
will undoubtedly be a far better understanding of stellar internal
properties and stellar evolution, together with an improved insight
into the physics of matter under the extreme conditions found in stars.
---------------------------------------------------------
Title: Kepler Mission: Mission Progress
Authors: Borucki, William J.; Koch, D. G.; Lissauer, J. J.; Basri,
G. S.; Caldwell, D. A.; DeVore, E.; Jenkins, J. M.; Caldwell, J. J.;
Christensen-Dalsgaard, J.; Cochran, W. D.; Dunham, E. W.; Gautier,
T. N.; Geary, J. C.; Latham, D. A.; Sasselov, D.; Gilliland, R. L.;
Gould, A.; Howell, S. B.; Brown, T. M.; Kondo, Y.; Monet, D. G.;
Batalha, N.
2006DPS....38.4501B Altcode: 2006BAAS...38..567B
Kepler is a Discovery-class mission designed to determine the
frequency of Earth-size planets in and near the habitable zone (HZ)
of solar-like stars. The instrument consists of a 0.95 m aperture
photometer designed to obtain high precision photometric measurements
of >100,000 stars to search for patterns of transits. The focal
plane of the Schmidt-telescope contains 42 CCDs with a total of 96
megapixels that cover 100 square degrees of sky. <P />Both the Schmidt
corrector and 1.4 m aperture primary mirror have been fabricated and
polished. All 50 CCD detectors have been delivered, tested and found to
perform better than required, and are now being mounted in modules to be
installed in the focal plane. Measurements of the ability of the first
module to detect transit amplitudes expected from Earth-size planets
are scheduled to start this month. A preliminary catalog classifying
11 million stars in the FOV has been produced. The science descope
that replaced the articulated antenna with a body-fixed antenna still
provides performance above the baseline design. A concise description of
the current mission design and expected science results are presented.
---------------------------------------------------------
Title: Computational Acoustics in Spherical Geometry: Steps toward
Validating Helioseismology
Authors: Hanasoge, S. M.; Larsen, R. M.; Duvall, T. L., Jr.; De Rosa,
M. L.; Hurlburt, N. E.; Schou, J.; Roth, M.; Christensen-Dalsgaard,
J.; Lele, S. K.
2006ApJ...648.1268H Altcode:
Throughout the past decade, detailed helioseismic analyses of
observations of solar surface oscillations have led to advances in our
knowledge of the structure and dynamics of the solar interior. Such
analyses involve the decomposition of time series of the observed
surface oscillation pattern into its constituent wave modes, followed
by inversion procedures that yield inferences of properties of the
solar interior. While this inverse problem has been a major focus in
recent years, the corresponding forward problem has received much less
attention. We aim to rectify this situation by taking the first steps
toward validating and determining the efficacy of the helioseismic
measurement procedure. The goal of this effort is to design a means
to perform differential studies of various effects such as flows and
thermal perturbations on helioseismic observables such as resonant
frequencies, travel-time shifts, etc. Here we describe our first
efforts to simulate wave propagation within a spherical shell,
which extends from 0.2 to about 1.0004 R<SUB>solar</SUB> (where
R<SUB>solar</SUB> is the radius of the Sun) and which possesses a
solar-like stratification. We consider a model containing no flows
that will serve as a reference model for later studies. We discuss the
computational procedure, some difficulties encountered in a simulation
of this kind, and the means to overcome them. We also present techniques
used to validate the simulation.
---------------------------------------------------------
Title: The Kepler Mission: Astrophysics and Eclipsing Binaries
Authors: Koch, D.; Borucki, W.; Basri, G.; Brown, T.; Caldwell, D.;
Christensen-Dalsgaard, J.; Cochran, W.; Dunham, E.; Gautier, T. N.;
Geary, J.; Gilliland, R.; Jenkins, J.; Kondo, Y.; Latham, D.; Lissauer,
J.; Monet, D.
2006Ap&SS.304..391K Altcode: 2006Ap&SS.tmp..467K
The Kepler Mission is a photometric space mission that will continuously
observe a single 100 square degree field of view (FOV) of the sky of
more than 100,000 stars in the Cygnus-Lyra region for four or more
years with a precision of 14 parts per million (ppm) for a 6.5 hour
integration including shot noise for a twelfth magnitude star. The
primary goal of the mission is to detect Earth-size planets in the
habitable zone of solar-like stars. In the process, many eclipsing
binaries (EB) will also be detected. Prior to launch, the stellar
characteristics will have been determined for all the stars in the FOV
with K<14.5. As part of the verification process, stars with transits
(about 5%) will need to have follow-up radial velocity observations
performed to determine the component masses and thereby separate
grazing eclipses caused by stellar companions from transits caused
by planets. The result will be a rich database on EBs. The community
will have access to the archive for uses such as for EB modeling of
the high-precision light curves. A guest observer program is also
planned for objects not already on the target list.
---------------------------------------------------------
Title: A new international project: Stellar Oscillations Network Group
Authors: Kjeldsen, H.; Grundahl, F.; Christensen-Dalsgaard, J.
2006IAUJD..17E..29K Altcode:
Stellar Oscillations Network Group (SONG) is a new international project
with the aim of developing a global network of automatic telescopes
of ~1m aperture devoted to asteroseismology and planet hunting with a
major fraction of the available time devoted to asteroseismology. The
project is undergoing a conceptual design study in 2006 and is still
in its very earliest phases. The network is expected to consist of 8
identical telescope-nodes, and will be operated as a single facility. A
timescale for the implementation of the project is not yet developed,
but it is realistic to expect that full operations can, at the earliest,
commence around 2010. SONG is planned to provide high S/N data for many
stars of different types, with emphasis being on long time-series work
lasting several weeks to months for selected targets. The network will
focus mainly on bright stars.
---------------------------------------------------------
Title: Introductory overview : a new era of asteroseismology
Authors: Christensen-Dalsgaard, J.
2006IAUJD..17E..17C Altcode:
In the last few years, asteroseismology of solar-like stars has been
converted from a dream to a solid reality. New observational facilities,
particularly very stable spectrographs, have allowed the detection
and study of oscillations in a number of stars on, and just after,
the main sequence, placing increasingly strong constraints on the
modelling of stellar interiors. Further great advances are expected in
the coming years, from continued ground- based efforts and from space
missions. Particularly interesting will be the results from CoRoT, to
be launched later this year; on a slightly longer time scale the NASA
Kepler mission is expected to provide asteroseismic data for a large
number of stars. The interpretation of these data will certainly start a
new era of realistic stellar modelling with a strong observational base.
---------------------------------------------------------
Title: Scientific Objectives of the Novel Formation Flying Mission
Aspiics
Authors: Turck-Chièze, S.; Schmutz, W.; Thuillier, G.; Jefferies,
S.; Pallé; Dewitt, S.; Ballot, J.; Berthomieu, G.; Bonanno, A.;
Brun, A. S.; Christensen-Dalsgaard, J.; Corbard, T.; Couvidat, S.;
Darwich, A. M.; Dintrans, B.; Domingo, V.; Finsterle, W.; Fossat,
E.; Garcia, R. A.; Gelly, B.; Gough, D.; Guzik, J.; Jiménez, A. J.;
Jiménez-Reyes, S.; Kosovichev, A.; Lambert, P.; Lefebvre, S.; Lopes,
I.; Martic, M.; Mathis, S.; Mathur, S.; Nghiem, P. A. P.; Piau, L.;
Provost, J.; Rieutord, M.; Robillot, J. M.; Rogers, T.; Roudier, T.;
Roxburgh, I.; Rozelot, J. P.; Straka, C.; Talon, S.; Théado, S.;
Thompson, M.; Vauclair, S.; Zahn, J. P.
2006ESASP.617E.164L Altcode: 2006soho...17E.164L
No abstract at ADS
---------------------------------------------------------
Title: The EUV Variability Experiment (EVE) on the Solar Dynamics
Observatory (SDO): Science Plan and Instrument Overview
Authors: Turck-Chièze, S.; Schmutz, W.; Thuillier, G.; Jefferies,
S.; Pallé; Dewitt, S.; Ballot, J.; Berthomieu, G.; Bonanno, A.;
Brun, A. S.; Christensen-Dalsgaard, J.; Corbard, T.; Couvidat, S.;
Darwich, A. M.; Dintrans, B.; Domingo, V.; Finsterle, W.; Fossat,
E.; Garcia, R. A.; Gelly, B.; Gough, D.; Guzik, J.; Jiménez, A. J.;
Jiménez-Reyes, S.; Kosovichev, A.; Lambert, P.; Lefebvre, S.; Lopes,
I.; Martic, M.; Mathis, S.; Mathur, S.; Nghiem, P. A. P.; Piau, L.;
Provost, J.; Rieutord, M.; Robillot, J. M.; Rogers, T.; Roudier, T.;
Roxburgh, I.; Rozelot, J. P.; Straka, C.; Talon, S.; Théado, S.;
Thompson, M.; Vauclair, S.; Zahn, J. P.
2006ESASP.617E.165W Altcode: 2006soho...17E.165W
No abstract at ADS
---------------------------------------------------------
Title: Helas-European Helio- and Asteroseismology Network
Authors: Roth, M.; Lühe, O. v. d.; Pallé, P.; Thompson, M.;
Christensen-Dalsgaard, J.; Monteiro, M. J. P. F. G; Gizon, L.; Di
Mauro, M. P.; Aerts, C.; Daszynska-Daszkiewicz, J.; Corbard, T.
2006ESASP.617E.157R Altcode: 2006soho...17E.157R
No abstract at ADS
---------------------------------------------------------
Title: The Dynamics Project
Authors: Turck-Chièze, S.; Schmutz, W.; Thuillier, G.; Jefferies,
S.; Pallé; Dewitt, S.; Ballot, J.; Berthomieu, G.; Bonanno, A.;
Brun, A. S.; Christensen-Dalsgaard, J.; Corbard, T.; Couvidat, S.;
Darwich, A. M.; Dintrans, B.; Domingo, V.; Finsterle, W.; Fossat,
E.; Garcia, R. A.; Gelly, B.; Gough, D.; Guzik, J.; Jiménez, A. J.;
Jiménez-Reyes, S.; Kosovichev, A.; Lambert, P.; Lefebvre, S.; Lopes,
I.; Martic, M.; Mathis, S.; Mathur, S.; Nghiem, P. A. P.; Piau, L.;
Provost, J.; Rieutord, M.; Robillot, J. M.; Rogers, T.; Roudier, T.;
Roxburgh, I.; Rozelot, J. P.; Straka, C.; Talon, S.; Théado, S.;
Thompson, M.; Vauclair, S.; Zahn, J. P.
2006ESASP.617E.162T Altcode: 2006soho...17E.162T
No abstract at ADS
---------------------------------------------------------
Title: Asteroseismology: the SONG of the Stars
Authors: Christensen-Dalsgaard, Jorgen
2006kas..confE..14C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Pinpointing isochrones in clusters .
Authors: Grundahl, F.; Arentoft, T.; Bruntt, H.; Christensen-Dalsgaard,
J.; Clausen, J. V.; Frandsen, S.; Glowienka, L.; Jensen, H. R.;
Kjeldsen, H.; Lefever, K.; Meibom, S.; Nielsen, T. B.; Pigulski, A.;
Southworth, J.
2006MmSAI..77..433G Altcode:
Detached eclipsing binaries allow the determination of accurate stellar
masses and radii. Here we present the first results of a programme
which aims at using such systems for the determination of accurate
stellar parameters in open star clusters and discuss this in relation
to the study of pulsating stars. As an example we show results for a
detached eclipsing system in the old open cluster NGC 188 and briefly
discuss the two intermediate age open clusters NGC 1817 and NGC 2506
which both contains pulsating stars and detached eclipsing binaries.
---------------------------------------------------------
Title: SONG: Stellar Oscillations Network Group . A global network
of small telescopes for asteroseismology and planet searches.
Authors: Grundahl, F.; Kjeldsen, H.; Frandsen, S.; Andersen, M.;
Bedding, T.; Arentoft, T.; Christensen-Dalsgaard, J.
2006MmSAI..77..458G Altcode:
One of the limiting factors in current asteroseismic investigations
of solar type stars is the limited time coverage of single-site
observations. To remedy this problem we are studying the design of
a global network based on 16-24 inch telescopes equipped with fibre
fed high-efficiency and high-resolution spectrographs and iodine
cells. These will measure precise radial velocity time-series for stars
in order to carry out asteroseismic analyses and search for low-mass
planets in short period orbits around our targets.
---------------------------------------------------------
Title: Probing the internal magnetic field of slowly pulsating
B-stars through g modes
Authors: Hasan, S. S.; Zahn, J. -P.; Christensen-Dalsgaard, J.
2005A&A...444L..29H Altcode: 2005astro.ph.11472H
Context: .<BR /> Aims: .We suggest that high-order g modes can be used
as a probe of the internal magnetic field of SPB (slowly pulsating
B) stars. The idea is based on earlier work by the authors hich
analytically investigated the effect of a vertical magnetic field on p
and g modes in a plane-parallel isothermal stratified atmosphere. It
was found that even a weak field can significantly shift the g-mode
frequencies - the effect increases with mode order.<BR /> Methods:
.In the present study we adopt the classical perturbative approach
to estimate the internal field of a 4 solar mass SPB star by looking
at its effect on a low-degree (l=1) and high-order (n=20) g mode with
a period of about 1.5 d. <BR /> Results: .We find that a polar field
strength of about 110 kG on the edge of the convective core is required
to produce a frequency shift of 1%. Frequency splittings of that order
have been observed in several SPB variables, in some cases clearly too
small to be ascribed to rotation. We suggest that they may be due to
a poloidal field with a strength of order 100 kG, buried in the deep
interior of the star.<BR /> Conclusions: .
---------------------------------------------------------
Title: Jets in the Solar Tachocline as Diagnostics of Global MHD
Processes
Authors: Christensen-Dalsgaard, J.; Corbard, T.; Dikpati, M.; Gilman,
P. A.; Thompson, M. J.
2005ASPC..346..115C Altcode:
Multiple theories predict the existence of prograde fluid jets in the
solar tachocline. We find helioseismic evidence of a prograde jet near
60° latitude in N and S hemispheres that persists through almost all
of the current solar cycle. This evidence favors a hydrodynamic origin
for the jet, from global instability of the differential rotation of
the tachocline. We see no evidence for jets that migrate toward the
equator with the advancing solar cycle, which tends to rule out jets
associated with toroidal field bands in the tachocline.
---------------------------------------------------------
Title: Kepler Mission Design
Authors: Koch, D. G.; Borucki, W. J.; Lissauer, J. J.; Basri, G. S.;
Gould, A. D.; Brown, T. M.; Caldwell, D. A.; DeVore, E. K.; Jenkins,
J. M.; Christensen-Dalsgaard, J.; Cochran, W. D.; Dunham, E. W.;
Gautier, T. N.; Geary, J. C.; Latham, D. W.; Gilliland, R. L.; Kondo,
Y.; Monet, D. G.
2005AAS...20711009K Altcode: 2005BAAS...37.1339K
The Kepler Mission is in the development phase with launch planned for
2008. The mission goal is to reliably detect a significant number of
Earth-size and smaller planets in the habitable zone of solar-like
stars. (see W. Borucki, et al, this meeting.) The mission design
allows for exploring the diversity of planetary sizes and orbital
periods for a wide variety of stellar spectral types, (see posters by
D. Latham, et al and T. Brown, et al, this meeting on stellar catalog
preparation). In this poster we describe the technical approach taken
for the mission design; describing the flight and ground system, the
detection methodology, the photometer design and capabilities, the way
the data are taken and processed, the Guest Observer opportunity and
the EPO aspects (see paper by E. DeVore, et al). Finally the detection
capability in terms of planet size is presented as a function of
planetary orbital period, mission duration, stellar type and combined
differential photometric precision.
---------------------------------------------------------
Title: Solar-like Oscillations in α Centauri B
Authors: Kjeldsen, Hans; Bedding, Timothy R.; Butler, R. Paul;
Christensen-Dalsgaard, Jørgen; Kiss, Laszlo L.; McCarthy, Chris;
Marcy, Geoffrey W.; Tinney, Christopher G.; Wright, Jason T.
2005ApJ...635.1281K Altcode: 2005astro.ph..8609K
We have made velocity observations of the star α Centauri B from two
sites, allowing us to identify 37 oscillation modes with l=0-3. Fitting
to these modes gives the large and small frequency separations as a
function of frequency. The mode lifetime, as measured from the scatter
of the oscillation frequencies about a smooth trend, is similar to that
in the Sun. Limited observations of the star δ Pav show oscillations
centered at 2.3 mHz, with peak amplitudes close to solar. We introduce
a new method of measuring oscillation amplitudes from heavily smoothed
power density spectra, from which we estimated amplitudes for α Cen α
and B, β Hyi, δ Pav, and the Sun. We point out that the oscillation
amplitudes may depend on which spectral lines are used for the velocity
measurements. <P />Based on observations collected at the European
Southern Observatory, Paranal, Chile (ESO Programme 71.D-0618).
---------------------------------------------------------
Title: Solar Convection-Zone Dynamics, 1995-2004
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R.;
Schou, J.; Thompson, M. J.
2005ApJ...634.1405H Altcode:
The nine-year span of medium-degree helioseismic data from the Global
Oscillation Network Group (GONG) and the Michelson Doppler Imager (MDI)
allows us to study the evolving zonal flows in the solar convection
zone over the rising phase, maximum, and early declining phase
of solar cycle 23. Using two independent two-dimensional rotation
inversion techniques, we investigate the depth profile of the flow
pattern known as the torsional oscillation. The observations suggest
that the flows penetrate deep within the convection zone-perhaps to
its base-even at low latitudes, and that the phase of the pattern is
approximately constant along lines of constant rotation rather than
lines of constant latitude.
---------------------------------------------------------
Title: Kepler Mission: Current Status
Authors: Borucki, W. J.; Koch, D. G.; Lissauer, J. J.; Basri,
G. S.; Caldwell, D. A.; DeVore, E.; Jenkins, J. M.; Caldwell, J. J.;
Christensen-Dalsgaard, J.; Cochran, W. D.; Dunham, E. W.; Gautier,
T. N.; Geary, J. C.; Latham, D. A.; Sasselov, D.; Gilliland, R. L.;
Gould, A.; Howell, S. B.; Kondo, Y.; Monet, D. G.
2005AAS...20715301B Altcode: 2005BAAS...37Q1412B
Kepler is a Discovery-class mission designed to determine the frequency
of Earth-size planets in and near the habitable zone (HZ) of solar-like
stars. The instrument consists of a 0.95 m aperture photometer designed
to obtain high precision photometric measurements of >100,000 stars
to search for patterns of transits. The depth and repetition time of
transits provide the size of the planet relative to the star and its
orbital period. At the end of the four year mission, several hundred
terrestrial planets should be discovered if such planets are common. <P
/>Multi-band ground-based observation of 5x10<SUP>6</SUP> stars in the
Kepler FOV is currently underway to estimate stellar parameters and
choose appropriate targets. The poster by Latham et al discusses the
filter set, magnitude range, and current status of the Kepler Input
Catalog. The poster by Brown et.al. describes the methods used to go
from these observations and stellar models to Teff and log(g). With
these parameters, dwarf stars can be selected and both the star and
planet diameters can be calculated. When transit patterns are detected,
the positions of discovered planets relative to the habitable zone
can be estimated. <P />Both the Schmidt corrector and 1.4 m aperture
primary mirror have been fabricated and are being polished. Forty-six
CCD detectors have been delivered, tested, and are being prepared for
mounting in modules that will be installed in the focal plane. As of
Oct. 2005, the first CCD driver, data acquisition, and science data
accumulator boards have been functionally tested. And Build 0 of the
flight software has been completed and tested. These support reading
out of the 96 megapixel focal plane as often as every 3 sec. A more
complete discussion of the spacecraft and instrument development can
be found in the poster by Koch et al.
---------------------------------------------------------
Title: How Sensitive are Rotation Inversions to Subtle Features of
the Dynamo?
Authors: Howe, R.; Rempel, M.; Christensen-Dalsgaard, J.; Schou, J.;
Thompson, M. J.; Komm, R.; Hill, F.
2005ASPC..346...99H Altcode:
Global rotation inversions can probe the pattern of zonal flows
well into the convection zone. In this paper, we test the ability
of the inversions to constrain the predictions of dynamo models. A
flux-transport dynamo model, including a mean-field theory of
differential rotation and allowing for feedback of the Lorentz force
on differential rotation and meridional flow, was used to produce a
22-year cycle of simulated rotation profiles. These were then subjected
to simulated inversions with realistic mode sets and errors, in order
to test how well the subtle subsurface features of the input profile
could be recovered. The preliminary results are quite encouraging.
---------------------------------------------------------
Title: The life of stars and their planets
Authors: Catala, C.; Aerts, C.; Aigrain, S.; Antonello, E.;
Appourchaux, T.; Auvergne, M.; Baglin, A.; Barge, P.; Barstow, M. A.;
Baudin, F.; Boumier, P.; Collier Cameron, A.; Christensen-Dalsgaard,
J.; Cutispoto, G.; Deeg, H.; Deleuil, M.; Desidera, S.; Donati, J. -F.;
Favata, F.; Foing, B. H.; Gameiro, J. F.; Garcia, R.; Garrido, F.;
Horne, K.; Lanza, A. F.; Lanzafame, A. C.; Lecavelier Des Etangs,
A.; Léger, A.; Mas-Hesse, M.; Messina, S.; Micela, G.; Michel, E.;
Monteiro, M. J. P. F. G.; Mosser, B.; Noels, A.; Pagano, I.; Piotto,
G.; Poretti, E.; Rauer, H.; Roca-Cortes, T.; Rodono, M.; Rouan, D.;
Roxburgh, I.; Schneider, J.; Strassmeier, K.; Turck-Chièze, S.;
Vauclair, S.; Vidal-Madjar, A.; Weiss, W. W.; Wheatley, P.
2005ESASP.588...99C Altcode: 2005tssc.conf...99C
We lack a reliable scenario for the formation and evolution of stars
and their planetary systems, involving key factors such as magnetic
fields and turbulence. We present the case for a mission concept that
will clarify these problems and give us a global view of the evolution
of combined star and planetary systems. This will be achieved by
simultaneously addressing the search for planetary transits in front
of a large number of stars, including many nearby stars, the study of
their internal structure and evolution via asteroseismology, and that
of their magnetic activity, via UV monitoring.
---------------------------------------------------------
Title: Influence of two updated nuclear reaction rates on the
evolution of low and intermediate mass stars
Authors: Weiss, A.; Serenelli, A.; Kitsikis, A.; Schlattl, H.;
Christensen-Dalsgaard, J.
2005A&A...441.1129W Altcode: 2005astro.ph..3408W
Two key reactions of hydrostatic nuclear burning in stars
have recently been revised by new experimental data - the
<SUP>14</SUP>N(p,γ)<SUP>15</SUP>0 and 3 α reaction rates. We
investigate how much the new rates influence the evolution of low-mass,
metal-poor and metal-free stars and of an intermediate-mass star of
solar-type composition. We concentrate on phases of helium ignition
or thermally unstable helium burning. Our global result is that
the new 3 α rate has no significant influence on such stars,
but that there is a noticeable though small effect of the new
<SUP>14</SUP>N(p,γ)<SUP>15</SUP>0 rate, in particular on the core
helium flash and the blue loop during core helium burning in the
intermediate-mass star.
---------------------------------------------------------
Title: Detection of granulation in the solar-like star Procyon A
Authors: Bruntt, H.; Kjeldsen, H.; Buzasi, D.; Christensen-Dalsgaard,
J.; Bedding, T. R.
2005ESASP.560..469B Altcode: 2005csss...13..469B
No abstract at ADS
---------------------------------------------------------
Title: Seismology of the Sun and solar-like stars
Authors: Christensen-Dalsgaard, J.
2005ESASP.560...81C Altcode: 2005csss...13...81C
No abstract at ADS
---------------------------------------------------------
Title: The non-detection of oscillations in Procyon by MOST: Is it
really a surprise?
Authors: Bedding, T. R.; Kjeldsen, H.; Bouchy, F.; Bruntt, H.; Butler,
R. P.; Buzasi, D. L.; Christensen-Dalsgaard, J.; Frandsen, S.; Lebrun,
J. -C.; Martić, M.; Schou, J.
2005A&A...432L..43B Altcode: 2005astro.ph..1662B
We argue that the non-detection of oscillations in Procyon by the
MOST satellite reported by [CITE] is fully consistent with published
ground-based velocity observations of this star. We also examine the
claims that the MOST observations represent the best photometric
precision so far reported in the literature by about an order of
magnitude and are the most sensitive data set for asteroseismology
available for any star other than the Sun. These statements are
not correct, with the most notable exceptions being observations
of oscillations in α Cen A that are far superior. We further
disagree that the hump of excess power seen repeatedly from velocity
observations of Procyon can be explained as an artefact caused by
gaps in the data. The MOST observations failed to reveal oscillations
clearly because their noise level is too high, possibly from scattered
Earthlight in the instrument. We did find an excess of strong peaks in
the MOST amplitude spectrum that is inconsistent with a simple noise
source such as granulation, and may perhaps indicate oscillations at
roughly the expected level.
---------------------------------------------------------
Title: Physics of Solar-Like Oscillations
Authors: Christensen-Dalsgaard, Jørgen
2005HiA....13..397C Altcode:
The physics of solar and stellar oscillations determine their observable
properties: frequencies amplitudes lifetimes line asymmetries and phase
relations. In the solar case these quantities have been measured often
with high precision and much has been learned about the properties of
the solar interior and the properties of the oscillations. I discuss
some examples of these inferences concentrating mostly on the low-degree
modes for which corresponding information may be expected for distant
stars. In addition I consider the current state of investigations
of solar-like oscillations in other stars and the prospects for an
improved understanding of the physics of such oscillations.
---------------------------------------------------------
Title: The use of frequency-separation ratios for asteroseismology
Authors: Otí Floranes, H.; Christensen-Dalsgaard, J.; Thompson, M. J.
2005MNRAS.356..671O Altcode: 2005MNRAS.356..671F
The systematic patterns of separations between frequencies of modes of
different degree and order are a characteristic of p-mode oscillations
of stars. The frequency separations depend on the internal structure
of the star and so measuring them in the observed oscillation spectra
of variable stars gives valuable diagnostics of the interior of a
star. Roxburgh & Vorontsov proposed using the ratio of the so-called
small frequency separation to the large frequency separation as a
diagnostic of the stellar interior, and demonstrated that this ratio
was less sensitive than the individual frequency separations themselves
to uncertain details of the near-surface structure. Here we derive
kernels relating the frequency separation ratio to structure, and show
why the ratio is relatively insensitive to the near-surface structure
in terms of the very small amplitude of the kernels in the near-surface
layers. We also investigate the behaviour of the separation ratio for
stars of different masses and ages, and demonstrate the usefulness of
the ratio in the so-called asteroseismic Hertzsprung-Russell diagram.
---------------------------------------------------------
Title: On helioseismic tests of basic physics
Authors: Christensen-Dalsgaard, J.; Di Mauro, M. P.; Schlattl, H.;
Weiss, A.
2005MNRAS.356..587C Altcode: 2004MNRAS.tmp..633C
An important goal of helioseismology is to provide information about
the basic physics and parameters that determine the structure of the
solar interior. Here we discuss the procedures applied in such analyses,
using as an example attempts to obtain significant constraints on the
value of Newton's gravitational constant G from helioseismology. The
analysis is based on complete direct and inverse helioseismic analysis
of a set of accurate observed acoustic frequencies. We confirm,
as found by previous investigations based on different approaches,
that the actual level of precision of the helioseismic inferences does
not allow us to constrain G with a precision better than that which
can be reached with direct experimental measurements. The conclusion
emphasizes the importance in helioseismic inferences of considering
not only the accuracy with which solar oscillations are measured,
but also the effect of uncertainties in other aspects of the model
computation and helioseismic analysis.
---------------------------------------------------------
Title: Detection of Jets and Associated Toroidal Fields in the
Solar Tachocline
Authors: Christensen-Dalsgaard, J.; Corbard, T.; Dikpati, M.; Gilman,
P. A.; Thompson, M. J.
2004ESASP.559..376C Altcode: 2004soho...14..376C
No abstract at ADS
---------------------------------------------------------
Title: How Sensitive are Rotation Inversions to Subtle Features of
the Dynamo?
Authors: Howe, R.; Rempel, M.; Christensen-Dalsgaard, J.; Hill, F.;
Komm, R. W.; Schou, J.; Thompson, M. J.
2004ESASP.559..468H Altcode: 2004soho...14..468H
No abstract at ADS
---------------------------------------------------------
Title: The Phase of the Torsional Oscillation Pattern
Authors: Howe, R.; Komm, R. W.; Hill, F.; Christensen-Dalsgaard, J.;
Schou, J.; Thompson, M. J.
2004ESASP.559..476H Altcode: 2004soho...14..476H
No abstract at ADS
---------------------------------------------------------
Title: An Overview of Helio- and Asteroseismology
Authors: Christensen-Dalsgaard, J.
2004ESASP.559....1C Altcode: 2004soho...14....1C
No abstract at ADS
---------------------------------------------------------
Title: An Introduction to Solar Oscillations and Helioseismology
Authors: Christensen-Dalsgaard, Jørgen
2004AIPC..731...18C Altcode:
Helioseismology offers unique possibilities for probing the detailed
internal structure of a star and, in this way, constraining the physical
properties of matter under stellar conditions. Here I provide a brief
introduction to stellar structure and stellar oscillations, as well as
to the techniques used in helioseismic analyses. In addition, I give a
few examples of the results obtained from helioseismic investigations
of solar structure.
---------------------------------------------------------
Title: Asteroseismology of Sun-Like Stars
Authors: Metcalfe, T. S.; Brown, T. M.; Christensen-Dalsgaard, J.
2004ESASP.559..567M Altcode: 2004soho...14..567M; 2004astro.ph..8127M
In the past decade, helioseismology has revolutionized our
understanding of the interior structure of the Sun. In the next decade,
asteroseismology will place this knowledge into context, by providing
structural information for dozens of pulsating stars across the H-R
diagram. Solar-like oscillations have already been detected from
the ground in a few stars, and several current and planned satellite
missions will soon unleash a flood of stellar pulsation data. Deriving
reliable seismological constraints from these observations will
require a significant improvement to our current analysis methods. We
are adapting a computational method, based on a parallel genetic
algorithm, to help interpret forthcoming observations of Sun-like
stars. This approach was originally developed for white dwarfs and
ultimately led to several interesting tests of fundamental physics,
including a key astrophysical nuclear reaction rate and the theory of
stellar crystallization. The impact of this method on the analysis of
pulsating white dwarfs suggests that seismological modeling of Sun-like
stars will also benefit from this approach.
---------------------------------------------------------
Title: Convection-Zone Dynamics from GONG and MDI, 1995-2004
Authors: Howe, R.; Komm, R. W.; Hill, F.; Christensen-Dalsgaard, J.;
Haber, D. A.; Schou, J.; Thompson, M. J.
2004ESASP.559..472H Altcode: 2004soho...14..472H
No abstract at ADS
---------------------------------------------------------
Title: Astronomy: Where are Procyon's quakes?
Authors: Christensen-Dalsgaard, Jørgen; Kjeldsen, Hans
2004Natur.430...29C Altcode:
The acoustic waves that ripple through the Sun should exist in other
stars too. But a search for these 'starquakes' in the nearby star
Procyon has found no evidence of them.
---------------------------------------------------------
Title: The internal solar rotation from helioseismology (Invited
Review)
Authors: Christensen-Dalsgaard, J.
2004IAUS..215..305C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: New theoretical developments in stellar pulsation
Authors: Christensen-Dalsgaard, Jørgen
2004ASPC..310....3C Altcode: 2004IAUCo.193....3C; 2004vslg.conf....3C
The basic properties of stellar oscillations are reasonably well
understood, allowing measurements of their frequencies to be used as
probes of stellar interiors. The detailed understanding of the processes
responsible for the oscillations, in the very broad range of stars
observed to pulsate, has improved substantially over the past decade,
as have the techinques for asteroseismic investigations on the basis
of the observations. Here I provide a brief overview of the theory of
stellar oscillations, emphasizing several cases of recent progress,
often inspired by new observational developments.
---------------------------------------------------------
Title: Interpretation of the solar-like pulsational behaviour of
η Bootis
Authors: Di Mauro, Maria Pia; Christensen-Dalsgaard, JØrgen; Paternò,
Lucio; D'Antona, Francesca
2004SoPh..220..185D Altcode:
HR 5235, better known as η Bootis, is a bright and well-known star
for which very accurate observations have recently enabled Kjeldsen
et al. (2003) and Carrier, Bouchy, and Eggenberger (2003) not only to
confirm the presence of solar-like oscillations, but also to identify
the excitation in the oscillation spectrum of several p-mode frequencies
with harmonic degrees l = 0 - 2. Here we show how such observational
success, through the calculation and the investigation of theoretical
structure models and the comparison of the observed oscillation spectra
with the predicted p-mode frequencies of oscillations, permits one to
draw conclusions about the actual evolutionary state of this star and on
the physical properties of its internal structure. The computation of
the structure models is based on the use of updated global parameters
and includes overshooting from the convective core. In particular,
we consider the effect on the stellar structure, and hence on the
theoretical frequencies, of employing different equations of state
and different formalisms to describe the convective energy transport.
---------------------------------------------------------
Title: Physics of solar-like oscillations
Authors: Christensen-Dalsgaard, JØrgen
2004SoPh..220..137C Altcode:
The physics of solar and stellar oscillations determines their
observable properties: frequencies, amplitudes, lifetimes, line
asymmetries and phase relations. In the solar case these quantities have
been measured, often with high precision, and much has been learned
about the properties of the solar interior, and the properties of
the oscillations. With recent advances in observational techniques,
such seismic investigations are now being extended to solar-like
oscillations in distant stars. I provide a brief overview of the basic
properties of stellar oscillations, and of the information about stellar
properties that may be inferred from them, concentrating mostly on the
low-degree modes for which information may be expected for distant
stars. In addition, I consider the current state of investigations
of solar-like oscillations in other stars, and the prospects for an
improved understanding of the physics of such oscillations.
---------------------------------------------------------
Title: ENEAS: the European Network of Excellence in AsteroSeismology
Authors: Aerts, C.; Baglin, A.; Christensen-Dalsgaard, J.; Goupil,
M. J.; Houdek, G.; Kjeldsen, H.; Kollath, Z.; Kurtz, D.; Lebreton,
Y.; Maceroni, C.; Noels, A.; Schwarzenberg-Czerny, A.; Škoda, P.;
Solano, E.; Thompson, M. J.
2004ESASP.538..247A Altcode: 2004sshp.conf..247A
Asteroseismology is one of the major important science topics in
astrophysics in the coming decade. Several recent breakthroughs have
indeed been made in Europe in this field. The observational data will
improve significantly in the near future, as upgraded ground-based
instruments are being built and two European asteroseismic space
missions are planned for launch between 2005 and 2008. They will
provide us for the first time with ultra-high-accuracy, high-temporal
resoluton data from space for stars other than the Sun. A successful
asteroseismic study involves many different steps, from state-of-the-art
raw data treatment to theoretical physical modelling of the oscillation
frequencies. Our network is set up to meet the needs of combining and
exchanging the different expertises of the participating institutes, of
training PhD students and of both training and exchanging post-doctoral
researchers. This will guarantee the most fruitful and efficient
exploitation of the very substantial investments that are being made in
Europe in future observations of stellar oscillations, strengthening
Europe's leading position in this research field. Also, it will be a
test-bed for the development of efficient procedures for collaboration
across the internet, involving a vast range of procedures and skills,
as well as extensive common use of a broad variety of data. Furthermore,
procedures will be incorporated for the joint training of students,
which is an essential part of our project.
---------------------------------------------------------
Title: Planet Detection Capabilities of the Eddington Mission
Authors: Deeg, Hans J.; Horne, Keith; Favata, Fabio; Eddington
Science Team; Aerts, C.; Antonello, E.; Badiali, M.; Catala, C.;
Christensen-Dalsgaard, J.; Gimenez, A.; Grenon, M.; Penny, A.; Rauer,
H.; Roxburgh, I. W.; Schneider, J.; Waltham, N. R.
2004IAUS..202..448D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Comparison of Solar p-Mode Parameters from MDI and GONG:
Mode Frequencies and Structure Inversions
Authors: Basu, S.; Christensen-Dalsgaard, J.; Howe, R.; Schou, J.;
Thompson, M. J.; Hill, F.; Komm, R.
2003ApJ...591..432B Altcode:
Helioseismic analysis of solar global oscillations allows investigation
of the internal structure of the Sun. One important test of the
reliability of the inferences from helioseismology is that the
results from independent sets of contemporaneous data are consistent
with one another. Here we compare mode frequencies from the Global
Oscillation Network Group and Michelson Doppler Imager on board SOHO
and resulting inversion results on the Sun's internal structure. The
average relative differences between the data sets are typically less
than 1×10<SUP>-5</SUP>, substantially smaller than the formal errors in
the differences; however, in some cases the frequency differences show
a systematic behavior that might nonetheless influence the inversion
results. We find that the differences in frequencies are not a result
of instrumental effects but are almost entirely related to the data
pipeline software. Inversion of the frequencies shows that their
differences do not result in any significant effects on the resulting
inferences on solar structure. We have also experimented with fitting
asymmetric profiles to the oscillation power spectra and find that,
compared with the symmetric fits, this causes no significant change
in the inversion results.
---------------------------------------------------------
Title: Interferometry and asteroseismology: The radius of tau Cet
Authors: Pijpers, F. P.; Teixeira, T. C.; Garcia, P. J.; Cunha, M. S.;
Monteiro, M. J. P. F. G.; Christensen-Dalsgaard, J.
2003A&A...406L..15P Altcode:
We have determined from interferometry the radius of the nearby star
tau Cet, using recent observations with the VINCI instrument on VLTI
using the siderostats. The limb-darkened disk diameter is determined,
with an unprecedented internal precision of 0.5%, to be 1.971 +/-
0.009_(int.)+/- 0.05_(ext.) mas, corresponding to a physical radius
of 0.773 +/- 0.004_(int.)+/- 0.02_(ext.) R<SUB>sun</SUB>. With this
determination tau Cet becomes a prime target for asteroseismic campaigns
to determine its internal structure, and thereby test stellar evolution
theory. We discuss implications for asteroseismology and present
predictions for oscillation properties. <P />Based on observations
collected at the European Southern Observatory, Chile.
---------------------------------------------------------
Title: Convective overshooting in the evolution and seismology of
eta Bootis
Authors: Di Mauro, M. P.; Christensen-Dalsgaard, J.; Kjeldsen, H.;
Bedding, T. R.; Paternò, L.
2003A&A...404..341D Altcode:
In the near future frequencies of solar-like oscillation will be
observed by the several planned space missions. In order to assess the
information that will be available from such observations, we consider
theoretical predictions of the frequency spectrum of oscillations
of the star eta Bootis, which shows solar-type pulsations. We present
results obtained by comparing “classical” evolution models with models
computed by taking into account overshooting from the convective core.
---------------------------------------------------------
Title: Stellar Astrophysical Fluid Dynamics
Authors: Thompson, Michael J.; Christensen-Dalsgaard, Jørgen
2003safd.book.....T Altcode:
Preface; 1. A selective overview Jørgen Christensen-Dalsgaard and
Michael J. Thompson; Part I. Stellar Convection and Oscillations:
2. On the diversity of stellar pulsations Wojciech A. Dziembowski;
3. Acoustic radiation and mode excitation by turbulent convection
Günter Houdek; 4. Understanding roAp stars Margarida S. Cunha; 5. Waves
in the magnetised solar atmosphere Colin S. Rosenthal; Part II. Stellar
Rotation and Magnetic Fields: 6. Stellar rotation: a historical survey
Leon Mestel; 7. The oscillations of rapidly rotating stars Michel
Rieutord; 8. Solar tachocline dynamics: eddy viscosity, anti-friction,
or something in between? Michael E. McIntyre; 9. Dynamics of the solar
tachocline Pascale Garaud; 10. Dynamo processes: the interaction of
turbulence and magnetic fields Michael Proctor; 11. Dynamos in planets
Chris Jones; Part III. Physics and Structure of Stellar Interiors:
12. Solar constraints on the equation of state Werner Däppen;
13. 3He transport and the solar neutrino problem Chris Jordinson;
14. Mixing in stellar radiation zones Jean-Paul Zahn; 15. Element
settling and rotation-induced mixing in slowly rotating stars Sylvie
Vauclair; Part IV. Helio- and Asteroseismology: 16. Solar structure
and the neutrino problem Hiromoto Shibahashi; 17. Helioseismic data
analysis Jesper Schou; 18. Seismology of solar rotation Takashi Sekii;
19. Telechronohelioseismology Alexander Kosovichev; Part V. Large-Scale
Numerical Experiments: 20. Bridges between helioseismology and models
of convection zone dynamics Juri Toomre; 21. Numerical simulations of
the solar convection zone Julian R. Elliott; 22. Modelling solar and
stellar magnetoconvection Nigel Weiss; 23. Nonlinear magnetoconvection
in the presence of a strong oblique field Keith Julien, Edgar Knobloch
and Steven M. Tobias; 24. Simulations of astrophysical fluids Marcus
Brüggen; Part VI. Dynamics: 25. A magic electromagnetic field Donald
Lynden-Bell; 26. Continuum equations for stellar dynamics Edward
A. Spiegel and Jean-Luc Thiffeault; 27. Formation of planetary systems
Douglas N. C. Lin; 28. The solar-cycle global warming as inferred from
sky brightness variation Wasaburo Unno and Hiromoto Shibahashi.
---------------------------------------------------------
Title: Transient oscillations near the solar tachocline
Authors: Toomre, Juri; Christensen-Dalsgaard, Jorgen; Hill, Frank;
Howe, Rachel; Komm, Rudolf W.; Schou, Jesper; Thompson, Michael J.
2003ESASP.517..409T Altcode: 2003soho...12..409T
We report on further developments in the 1.3-yr quasi-periodic
oscillations reported by Howe et al. (2000). These are small (6 to 8
nHz peak-to-peak) oscillations in the inferred rotation rate near the
bottom of the convection zone and in the outer part of the radiative
interior. The oscillations are strongest and most coherent at about a
fractional radius of 0.72 in the equatorial region. Further monitoring
of the oscillations near the equator shows that they continued for a
period after the end of the data analyzed by Howe et al., but appear to
have now diminished in amplitude. This is reminiscent of the transient
behavior of similar (1.3 to 1.4 yr) periodicities in solar-wind and
geomagnetic datasets previously reported. We speculate that the near
tachocline oscillation is associated with the rising phase of the
solar cycle. We discuss tests performed to eliminate various possible
explanations of the oscillations due to systematic errors in the data
and in their analyses.
---------------------------------------------------------
Title: Radial Oscillations in A Stars
Authors: Medupe, R.; Christensen-Dalsgaard, J.; Kurtz, D. W.
2003ASPC..305..146M Altcode: 2003mfob.conf..146M
No abstract at ADS
---------------------------------------------------------
Title: Physics of Solar-Like Oscillations
Authors: Christensen-Dalsgaard, Jørgen
2003IAUJD..12E..55C Altcode:
The physics of solar and stellar oscillations determine their observable
properties: frequencies amplitudes lifetimes line asymmetries and phase
relations. In the solar case these quantities have been measured often
with high precision and much has been learned about the properties of
the solar interior and the properties of the oscillations. I discuss
some examples of these inferences concentrating mostly on the low-degree
modes for which corresponding information may be expected for distant
stars. In addition I consider the current state of investigations
of solar-like oscillations in other stars and the prospects for an
improved understanding of the physics of such oscillations.
---------------------------------------------------------
Title: A Study of the Solar-Like Properties of β Hydri
Authors: Di Mauro, Maria Pia; Christensen-Dalsgaard, Jørgen;
Paternò, Lucio
2003Ap&SS.284..229D Altcode:
We investigate properties of the internal structure of HR2021, better
known as β Hydri, a G2 IV subgiant with mass close to solar and for
which observations by Bedding et al. (2001) have shown the presence of
solar-like oscillations. We have computed models of β Hydri, based
on updated global parameters, and compared the computed frequencies
for the models with the observed oscillation spectrum.
---------------------------------------------------------
Title: The European Ultra-High Precision Stellar Photometry Road
Map for Asteroseismology and Planet Finding
Authors: Roxburgh, Ian; Favata, Fabio; Baglin, Annie;
Christensen-Dalsgaard, Jørgen
2003acfp.conf..479R Altcode:
We give a brief description of the 3 European space missions COROT,
MONS and Eddington, devoted to asteroseismology and planet finding.
---------------------------------------------------------
Title: Rotation of the solar interior
Authors: Christensen-Dalsgaard, J.; Thompson, M. J.
2003dysu.book...55C Altcode:
Helioseismology allows us to infer the rotation in the greater part
of the solar interior with high precision and resolution. The results
show interesting conflicts with earlier theoretical expectations,
indicating that the Sun is host to complex dynamical phenomena, so
far hardly understood. This has important consequences for our ideas
about the evolution of stellar rotation, as well as for models for
the generation of the solar magnetic field. An overview of our current
knowledge about solar rotation is given, much of it obtained from the
SOHO spacecraft, and the broader implications are discussed.
---------------------------------------------------------
Title: Preface (Stellar astrophysical fluid dynamics)
Authors: Thompson, Michael J.; Christensen-Dalsgaard, Jørgen
2003safd.bookD...9T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On Asteroseismic Constraints for Modelling the δ Scuti Stars
V480 Tau and θ<SUP>2</SUP> Tau A
Authors: Di Mauro, M. P.; Pijpers, F.; Christensen-Dalsgaard, J.;
Paternò, L.; Teixeira, T.; Thompson, M. J.
2003ASPC..305..161D Altcode: 2003mfob.conf..161D
We investigate the structure and evolution of δ Scuti stars and
discuss how basic properties as well as global oscillation frequencies
are modified by moderate rotation. We present theoretical analyses of
V480 Tau, observed during the MUSICOS 1996 campaign (Hao et al. 2001),
and of θ<SUP>2</SUP> Tau A, monitored by the WIRE satellite (Poretti
et al. 2002). We compare the observed spectra of frequencies with the
theoretical oscillation frequencies calculated by including rotational
effects.
---------------------------------------------------------
Title: Seismological analysis of the Helium ionization zones in low-
and moderate-mass stars
Authors: Miglio, A.; Christensen-Dalsgaard, J.; di Mauro, M. P.;
Monteiro, M. J. P. F. G.; Thompson, M. J.
2003aahd.conf..537M Altcode:
The region of the second ionization of helium in solar-like stars is a
narrow subsurface layer whose thermodynamic properties are responsible
for the presence of a characteristic signature in the oscillation
frequencies of the p modes. Here, with the aim of detecting the acoustic
depth of the second helium ionization zone, we consider two methods
of analysing the signal generated in the oscillation frequencies by
the sharp decrease in the first adiabatic exponent Γ<SUB>1</SUB>,
which occurs where ionization takes place. The properties of the
ionization zone, once determined by seismological means, may be used
to put constraints on the structure of the stars, in particular on
the envelope helium abundance.
---------------------------------------------------------
Title: Giant Vibrations in Dip
Authors: Teixeira, T. C.; Christensen-Dalsgaard, J.; Carrier, F.;
Aerts, C.; Frandsen, S.; Stello, D.; Maas, T.; Burnet, M.; Bruntt,
H.; de Medeiros, J. R.; Bouchy, F.; Kjeldsen, H.; Pijpers, F.
2003Ap&SS.284..233T Altcode:
This work reports the discovery of solar-type oscillations in the
giant star ξ Hydrae.
---------------------------------------------------------
Title: The Effect of Rotation on Stellar Oscillations
Authors: Karami, Kayoomars; Christensen-Dalsgaard, Joergen; Pijpers,
Frank P.
2003IAUJD..12E..29K Altcode:
Here we investigate the effect of rotation up to third order on normal
'p' and 'g' modes based on the formalism developed by Soufi Goupil
and Dziembowski (1998). As demonstrated by those authors the third
order perturbation formalism shows that: i) By taking into account
parts of the effects of Coriolis force in the zeroth order system the
computation reduces to solving the eigenvalue problem up to cubic order
without having to solve successive equations for the eigenfunctions at
each order and also the usual m-degeneracy occurring in the absence
of rotation is removed. ii) Near-degenerate coupling due to rotation
only occurs between modes with either the same degree l (and different
radial orders) or with degrees which differ by ±2. The total coupling
coefficients are caused by the three distinct terms including Coriolis
contribution non-spherically symmetric distortion and distortion and
Coriolis coupling. Our study shows that the third-order perturbation
formalism presented by Soufi Goupil and Dziembowski (1998) should be
revised by adding or correcting some terms in the equations. We also
carry out the numerical calculations for calculating the frequency
corrections up to third order for zero-age main-sequence and somewhat
evolved models of β Cephi stars.
---------------------------------------------------------
Title: Solar-Like Oscillations in the Giant Star XI Hydrae
Authors: Stello, Dennis; Carrier, Fabien; Aerts, Conny; Frandsen,
Søren; Bouchy, Francois; Kjeldsen, Hans; Teixeira, Teresa; Pijpers,
Frank; Christensen-Dalsgaard, Jørgen
2003IAUJD..12E..35S Altcode:
The discovery of solar-like oscillations in the giant star xi Hydrae
(G7III) was reported by Frandsen et al. (2002). In this talk we present
a much larger and more complete analysis of the data presented by
Frandsen et al. (2002) including an improved analysis containing
new stellar models (models for helium core burning stars). We also
present a large number of simulations that are used to quantify the
alias problem in the data set (caused by single site observations) and
hence making it possible to distinguish between detected frequencies
which should be trusted as real modes and those that are probably due
to sideband structures.
---------------------------------------------------------
Title: Problems, Connections and Expectations of Asteroseismology:
a Summary of the Workshop
Authors: Christensen-Dalsgaard, Jørgen
2003Ap&SS.284..277C Altcode:
The workshop took place at the beginning of what promises to be
a golden age of asteroseismology. Ground-based instrumentation
is finally reaching a level of stability which allows detailed
investigations of solar-like oscillations in at least bright, slowly
rotating main-sequence stars. Very extensive results are expected
from the coming space missions, including data on a broad range of
stars from the Eddington mission. The observational situation is
therefore extremely promising. To make full use of these promises,
major efforts are required towards the efficient utilization of the
data, through the development of techniques for the analysis and
interpretation of the data. A broad range of topics related to these
issues is discussed in the present proceedings. Here I review some
of the relevant problems, relate the asteroseismic investigations to
broader areas of astrophysics and consider briefly the basis for our
great expectations for the development of the field.
---------------------------------------------------------
Title: Commission 27: Variable stars (Etoiles variables)
Authors: Christensen-Dalsgaard, Jørgen
2003IAUTA..25..271C Altcode: 2003IAUTr..25A.271C
No abstract at ADS
---------------------------------------------------------
Title: A Danish space project: MONS - measuring oscillations in
nearby stars
Authors: Kjeldsen, H.; Christensen-Dalsgaard, J.; Bedding, T. R.
2003AdSpR..31..363K Altcode:
The MONS (Measuring Oscillations in Nearby Stars) project on the
Rømer satellite aims at studying properties of stellar interiors
through observations of oscillations in stellar luminosity and surface
temperature. The main targets are stars exhibiting oscillations similar
to those observed in the Sun, with very low amplitudes. During the
planned two-year life time of the mission, around 20 such stars will be
observed with the MONS Main Telescope. Additional data on variability
of a large number of stars of a broad range of types may be obtained
from the parallel science programme. This part of the programme will
use two instruments; The Star Trackers and the Field Monitor. The
following paper aims at describing some aspects of the MONS project.
---------------------------------------------------------
Title: A selective overview
Authors: Christensen-Dalsgaard, Jørgen; Thompson, Michael J.
2003safd.book....1C Altcode:
Contents: 1. Introduction. 2. On taking mixing-length
theory seriously. 3. The solar spoon. 4. Deep roots of solar
cycles. 5. Helioseismology: oscillations as a diagnostic of
the solar interior. 6. Inverting helioseismic data. 7. On the
detection of subphotospheric convective velocities and temperature
fluctuations. 8. Prospects for asteroseismic inference.
---------------------------------------------------------
Title: The Effect of Rotation on Stellar Oscillations
Authors: Karami, Kayoomars; Christensen-Dalsgaard, Joergen; Pijpers,
Frank P.
2003IAUJD..12E..28K Altcode:
Here we investigate the effect of rotation up to third order in terms of
the angular velocity of a star on normal 'p' and 'g' modes based on the
formalism developed by Soufi et al. (1998). Third order perturbation
formalism shows that: i) By taking into account parts of the effects
of Coriolis force in the zeroth order system the computation reduces to
solving the eigenvalue problem up to cubic order without having to solve
successive equations for the eigenfunctions at each order and also the
usual m-degeneracy occurring in the absence of rotation is removed. ii)
Near-degenerate coupling due to rotation only occurs between modes with
either the same degree l (and different radial orders) or with degrees
which differ by ±2. The total coupling coefficients are caused by the
three distinct terms including Coriolis contribution non-spherically
symmetric distortion and distortion and Coriolis coupling. Our study
shows that the third-order perturbation formalism presented by Soufi
et al. (1998) should be revised by adding or correcting some terms
in the equations. We also carry out the numerical calculations for
calculating the frequency corrections up to third order for zero-age
main-sequence and somewhat evolved models of β Cephi stars.
---------------------------------------------------------
Title: The Internal Rotation of the Sun
Authors: Thompson, Michael J.; Christensen-Dalsgaard, Jørgen; Miesch,
Mark S.; Toomre, Juri
2003ARA&A..41..599T Altcode:
Helioseismology has transformed our knowledge of the Sun's
rotation. Earlier studies revealed the Sun's surface rotation,
but now a detailed observational picture has been built up of the
internal rotation of our nearest star. Unlike the predictions of
stellar-evolution models, the radiative interior is found to rotate
roughly uniformly. The rotation within the convection zone is also
very different from prior expectations, which had been that the
rotation rate would depend primarily on the distance from the rotation
axis. Layers of rotational shear have been discovered at the base of
the convection zone and in the subphotospheric layers. Studies of the
time variation of rotation have uncovered zonal-flow bands, extending
through a substantial fraction of the convection zone, which migrate
over the course of the solar cycle, and there are hints of other
temporal variations and of a jet-like structure. At the same time,
building on earlier work with mean-field models, researchers have made
great progress in supercomputer simulations of the intricate interplay
between turbulent convection and rotation in the Sun's interior. Such
studies are beginning to transform our understanding of how rotation
organizes itself in a stellar interior.
---------------------------------------------------------
Title: HARPS: ESO's coming planet searcher. Chasing exoplanets with
the La Silla 3.6-m telescope
Authors: Pepe, F.; Mayor, M.; Rupprecht, G.; Avila, G.; Ballester,
P.; Beckers, J. -L.; Benz, W.; Bertaux, J. -L.; Bouchy, F.; Buzzoni,
B.; Cavadore, C.; Deiries, S.; Dekker, H.; Delabre, B.; D'Odorico,
S.; Eckert, W.; Fischer, J.; Fleury, M.; George, M.; Gilliotte, A.;
Gojak, D.; Guzman, J. -C.; Koch, F.; Kohler, D.; Kotzlowski, H.;
Lacroix, D.; Le Merrer, J.; Lizon, J. -L.; Lo Curto, G.; Longinotti,
A.; Megevand, D.; Pasquini, L.; Petitpas, P.; Pichard, M.; Queloz,
D.; Reyes, J.; Richaud, P.; Sivan, J. -P.; Sosnowska, D.; Soto, R.;
Udry, S.; Ureta, E.; van Kesteren, A.; Weber, L.; Weilenmann, U.;
Wicenec, A.; Wieland, G.; Christensen-Dalsgaard, J.; Dravins, D.;
Hatzes, A.; Kürster, M.; Paresce, F.; Penny, A.
2002Msngr.110....9P Altcode:
An extensive review of past, present and future research on extrasolar
planets is given in the article “Extrasolar Planets” by N. Santos
et al. in the present issue of The Messenger. Here we want to mention
only that the search for extrasolar planets and the interpretation of
the scientific results have evolved in recent years into one of the
most exciting and dynamic research topics in modern astronomy.
---------------------------------------------------------
Title: Helioseismic investigation of the solar envelope
Authors: di Mauro, M. P.; Christensen-Dalsgaard, J.
2002ESASP.506..879D Altcode: 2002svco.conf..879D; 2002ESPM...10..879D
It has already been demonstrated that the solar envelope can be
probed with sufficiently high spatial resolution through inversion
of high-degree acoustic modes, which unfortunately appear strongly
affected by uncertainties of the surface layers. In order to suppress
those uncertainties, we introdue the use of a suitable procedure to
be adopted in the helioseismic inversions of high-degree modes and
show new results on the properties of the Sun's interior.
---------------------------------------------------------
Title: Helioseismology
Authors: Christensen-Dalsgaard, Jørgen
2002RvMP...74.1073C Altcode: 2002astro.ph..7403C
Oscillations detected on the solar surface provide a unique opportunity
for investigations of the interior properties of a star. Through major
observational efforts, including extensive observations from space,
as well as through the development of sophisticated tools for the
analysis and interpretation of the data, we have been able to infer
the large-scale structure and rotation of the solar interior with
substantial accuracy. In addition, information is emerging about the
complex subsurface structure and dynamics of sunspot regions, which
dominate the magnetic activity in the solar atmosphere and beyond. The
results provide a detailed test of the modeling of stellar structure
and evolution, and hence of the physical properties of matter assumed
in the models. In this way the basis for using stellar modeling in
other branches of science is substantially strengthened; an important
example is the use of observations of solar neutrinos to constrain
the properties of the neutrino.
---------------------------------------------------------
Title: Detection of Solar-like oscillations in the G7 giant star
ξ Hya
Authors: Frandsen, S.; Carrier, F.; Aerts, C.; Stello, D.; Maas, T.;
Burnet, M.; Bruntt, H.; Teixeira, T. C.; de Medeiros, J. R.; Bouchy,
F.; Kjeldsen, H.; Pijpers, F.; Christensen-Dalsgaard, J.
2002A&A...394L...5F Altcode: 2002astro.ph..9325F
We report the firm discovery of solar-like oscillations in a giant
star. We monitored the star xi Hya (G7III) continuously during one
month with the CORALIE spectrograph attached to the 1.2 m Swiss Euler
telescope. The 433 high-precision radial-velocity measurements clearly
reveal multiple oscillation frequencies in the range 50-130 muHz,
corresponding to periods between 2.0 and 5.5 hours. The amplitudes
of the strongest modes are slightly smaller than 2 ms. Current model
calculations are compatible with the detected modes. <P />Based on
observations obtained with the CORALIE spectrograph on the 1.2-m Swiss
Euler telescope at La Silla, Chile.
---------------------------------------------------------
Title: Solar internal rotation as seen from SOHO MIDI data
Authors: Vorontsov, S. V.; Christensen-Dalsgaard, J.; Schou, J.;
Strakhov, V. N.; Thompson, M. J.
2002ESASP.508..111V Altcode: 2002soho...11..111V
We report results of inverting the rotational splittings of solar
p-mode frequencies measured from the MDI data, using an adaptive
regularization technique as described by Strakhov & Vorontsov
(2001). We analyse the spatial and temporal structure of the variations
in the internal rotation, which constitute the 11-yr solar torsional
oscillations. We employ all the data collected over half a solar cycle
to analyse further the time-independent component of the differential
rotation, particularly focusing on the solar tachocline region. We
address systematic errors in the rotational splitting measurements,
as indicated by the inversion residuals, which appear to restrict the
accuracy of the current helioseismic measurements.
---------------------------------------------------------
Title: Helioseismic Measurement of Solar Torsional Oscillations
Authors: Vorontsov, S. V.; Christensen-Dalsgaard, J.; Schou, J.;
Strakhov, V. N.; Thompson, M. J.
2002Sci...296..101V Altcode:
Bands of slower and faster rotation, the so-called torsional
oscillations, are observed at the Sun's surface to migrate in latitude
over the 11-year solar cycle. Here, we report on the temporal variations
of the Sun's internal rotation from solar p-mode frequencies obtained
over nearly 6 years by the Michelson Doppler Imager (MDI) instrument
on board the Solar and Heliospheric Observatory (SOHO) satellite. The
entire solar convective envelope appears to be involved in the torsional
oscillations, with phase propagating poleward and equatorward from
midlatitudes at all depths throughout the convective envelope.
---------------------------------------------------------
Title: Inferences on the solar envelope with high-degree modes
Authors: Di Mauro, M. P.; Christensen-Dalsgaard, J.; Rabello-Soares,
M. C.; Basu, S.
2002A&A...384..666D Altcode:
We investigate the structure of the Sun by helioseismic inversion of
a set of p-mode frequencies which includes new precise observations of
modes with high degree (l < 1000) obtained from the MDI instrument
on the SOHO satellite (Rhodes et al. \cite{rh98}). Such data have
the potential to improve the resolution of the solar structure in the
near-surface region, to provide detailed tests of the equation of state
and constrain the envelope helium abundance. In order to suppress the
uncertainties in the treatment of the surface layers in helioseismic
inversion procedures, we introduce here the use of a new surface term,
developed on the basis of higher-order asymptotic theory of acoustic
modes and suitable for the handling of high-degree mode frequencies.
---------------------------------------------------------
Title: A Comparison of Solar p-Mode Parameters from the Michelson
Doppler Imager and the Global Oscillation Network Group: Splitting
Coefficients and Rotation Inversions
Authors: Schou, J.; Howe, R.; Basu, S.; Christensen-Dalsgaard, J.;
Corbard, T.; Hill, F.; Komm, R.; Larsen, R. M.; Rabello-Soares, M. C.;
Thompson, M. J.
2002ApJ...567.1234S Altcode:
Using contemporaneous helioseismic data from the Global Oscillation
Network Group (GONG) and Michelson Doppler Imager (MDI) onboard SOHO,
we compare frequency-splitting data and resulting inversions about the
Sun's internal rotation. Helioseismology has been very successful in
making detailed and subtle inferences about the solar interior. But
there are some significant differences between inversion results
obtained from the MDI and GONG projects. It is important for making
robust inferences about the solar interior that these differences are
located and their causes eliminated. By applying the different analysis
pipelines developed by the projects not only to their own data but
also to the data from the other project, we conclude that the most
significant differences arise not from the observations themselves
but from the different frequency estimation analyses used by the
projects. We find that the GONG pipeline results in substantially fewer
fitted modes in certain regions. The most serious systematic differences
in the results, with regard to rotation, appear to be an anomaly in
the MDI odd-order splitting coefficients around a frequency of 3.5 mHz
and an underestimation of the low-degree rotational splittings in the
GONG algorithm.
---------------------------------------------------------
Title: Mini-ASTROD: mission concept
Authors: Ni, Wei-Tou; Zhu, Jin; Wu, Xiang-Ping; Chu, Guey-Bo; Yang,
Bin; Gao, Jian; Guan, Min; Tang, Chien-Jen; Chou, Yi; Chang, Chung-Hao;
Huang, Tian-Yi; Qu, Qin-Yue; Yi, Zhao-Hua; Li, Guang-Yu; Tao, Jin-He;
Wu, An-Ming; Luo, Jun; Yeh, Hsien-Chi; Zhou, Ze-Bing; Xiong, Yao-Heng;
Bi, Shao-Lan; Xu, Chong-Ming; Wu, Xue-Jun; Tang, Meng-Xi, Bao, Yun;
Li, Fang-Yu; Huang, Cheng; Yang, Fu-Min; Ye, Shu-Hua; Zhang, Shu-Lian;
Zhang, Yuan-Zhong; Nie, Yu-Xin; Chen, Guang; Christensen-Dalsgaard,
Joergen; Dittus, Hansjoerg; Fujii, Yasunori; Laemmerzahl, Claus;
Mangin, Jean Francois; Peters, Achim; Ruediger, Albrecht; Samain,
Etienne; Schiller, Stephan
2002PYunO..91..123N Altcode:
Advances in laser physics and its applications triggered the proposition
and development of Laser Astrodynamics. Mini-ASTROD is a down-scaled
version of ASTROD (Astrodynamical Space Test of Relativity using Optical
Devices). This mission concept has one spacecraft carrying a payload
of a telescope, six lasers, and a clock together with ground stations
(ODSN: Optical Deep Space Network) to test the optical scheme and yet
give important scientific results. These scientific results include
a better measurement of the relativistic parameters (gamma to 1 ppm,
beta to a few ppm and others with improvement), a better sensitivity
in using optical Doppler tracking method for detecting gravitational
waves, a potential of measuring the solar angular momentum via
Lense-Thirring effect and measurement of many solar system parameters
more precisely. These enable us to build a more precise ephemeris and
astrodynamics. The weight of this spacecraft is estimated to be about
300 - 350 kg with a payload of about 100 - 120 kg. The spacecraft goes
into an inner solar orbit with several options. We discuss the payload
configuration and outlook for technological developments to reach the
mission goals, and summarize the conclusions and recommendations of
the first and second organizational meetings for Mini-ASTROD study.
---------------------------------------------------------
Title: Solar g-Mode Oscillations
Authors: Christensen-Dalsgaard, Jørgen
2002IJMPD..11..995C Altcode:
In the early days of helioseismology, around 1975, independent
detections of an oscillation with a period of 160 min in solar spectral
line-shift data caused very substantial interest: it was suggested
that this resulted from a solar g mode, whose frequency would then
provide a tight constraint on the structure of the solar core. Also,
it was noted that such modes, which involve a substantial fraction
of the solar mass, might lead to a detectable gravitational-wave
signal. Later observations have, however, failed to confirm the solar
nature of the originally detected oscillation. Extensive data on the
low-frequency part of the solar oscillation spectrum have been obtained
from several experiments over the last decade, including instruments on
the SOHO spacecraft. These have provided stringent limits on amplitudes
of solar g modes and a few tentative detections, although so far not
independently confirmed. Theoretical estimates of g-mode amplitudes,
while highly uncertain, suggest that direct detection of the modes on
the solar surface may be difficult. However, detection with the ASTROD
mission may be possible, although identification of the solar signal
will require careful analysis.
---------------------------------------------------------
Title: Radial and Nonradial Pulsations as Probes of Stellar Physics
Authors: Aerts, Conny; Bedding, Timothy R.; Christensen-Dalsgaard,
Jørgen
2002ASPC..259.....A Altcode: 2002IAUCo.185.....A; 2002rnpp.conf.....A
No abstract at ADS
---------------------------------------------------------
Title: Mini-ASTROD
Authors: Ni, Wei-Tou; Zhu, Jin; Wu, Xiang-Ping; Chu, Guey-Bo; Yang,
Bin; Gao, Jian; Guan, Min; Tang, Chien-Jen; Chou, Yi; Chang, Chung-Hao;
Huang, Tianyi; Qu, Qin-Yue; Yi, Zhao-Hua; Li, Guangyu; Tao, Jinhe; Wu,
An-Ming; Luo, Jun; Yeh, Hsien-Chi; Zhou, Ze-Bing; Xiong, Yaoheng; Bi,
Shao-Lan; Xu, Chongming; Wu, Xue-Jun; Tang, Meng-Xi; Bao, Yun; Li,
Fangyu; Huang, Cheng; Yang, Fu-Min; Ye, Shu-Hua; Zhang, Shu-Lian;
Zhang, Yuan-Zhong; Nie, Yuxin; Chen, Guang; Christensen-Dalsgaard,
Jørgen; Dittus, Hansjörg; Fujii, Yasunori; Lämmerzahl, Claus;
Mangin, Jean François; Peters, Achim; Rüdiger, Albrecht; Samain,
Étienne; Schiller, Stephan
2002IJMPD..11.1035N Altcode:
Advances in laser physics and its applications triggered the proposition
and development of Laser Astrodynamics. Mini-ASTROD is a down-scaled
version of ASTROD (Astro-dynamical Space Test of Relativity using
Optical Devices). This mission concept has one spacecraft carrying a
payload of a telescope, six lasers, and a clock together with ground
stations (ODSN: Optical Deep Space Network) to test the optical
scheme and yet give important scientific results. These scientific
results include a better measurement of the relativistic parameters
(γ to 1 ppm, β to a few ppm and others with improvement), a better
sensitivity (several times better) in using the optical Doppler tracking
method for detecting gravitational waves, a potential of measuring the
solar angular momentum via the Lense-Thirring effect and measurement
of many solar system parameters more precisely. These enable us to
build a more precise ephemeris and astrodynamics. The weight of this
spacecraft is estimated to be about 300-350 kg with a payload of
about 100-120 kg. The spacecraft goes into an inner solar orbit with
several options. One option is with period 304 days as for the inner
spacecraft of the standard two-spacecraft ASTROD mission concept and
it takes about 900 days to reach the other side of the Sum relative
to the Earth. Another option is to launch with initial period about
290 days and to pass by Venus twice to receive gravity-assistance
for achieving shorter periods. For a launch on November 15, 2008,
after two encounters with Venus, the orbital period can be shortened
to 165 days. After about 400 days from launch, the spacecraft will
arrive at the other side of the Sun and the relativistic parameter γ
can be determined to 1 ppm. We discuss the payload configuration and
outlook for technological developments to reach the mission goals,
and summarize the conclusions and recommendations of the first and
second organizational meeting for the Mini-ASTROD study.
---------------------------------------------------------
Title: SOLA inversions for the core structure of solar-type stars
Authors: Basu, S.; Christensen-Dalsgaard, J.; Thompson, M. J.
2002ESASP.485..249B Altcode: 2002sshp.conf..249B; 2001astro.ph.10446B
The Subtractive Optimally Localized Averages (SOLA) method, developed
and extensively used in helioseismology, is applied to artificial data
to obtain measures of the sound speed inside a solar-type star. In
contrast to inversion methods which fit models to some aspect of
the data, methods such as SOLA provide an honest assessment of
what can truly be resolved using seismic data, without introducing
additional assumptions such as that the space of admissible stellar
models is small. The resulting measures obtained from SOLA inversion
can subsequently be used to eliminate putative stellar models. Here
we present results of experiments to test the reliability of SOLA
inferences using solar models and models of solar-type stars.
---------------------------------------------------------
Title: On inverting asteroseismic data
Authors: Thompson, M. J.; Christensen-Dalsgaard, J.
2002ESASP.485...95T Altcode: 2002sshp.conf...95T; 2001astro.ph.10447T
Some issues of inverting asteroseismic frequency data are discussed,
including the use of model calibration and linearized inversion. An
illustrative inversion of artificial data for solar-type stars,
using least-squares fitting of a small set of basis functions, is
presented. A few details of kernel construction are also given.
---------------------------------------------------------
Title: Asteroseismic inference for solar-type stars
Authors: Monteiro, M. J. P. F. G.; Christensen-Dalsgaard, J.; Thompson,
M. J.
2002ESASP.485..291M Altcode: 2001astro.ph.10445M; 2002sshp.conf..291M
The oscillation spectra of solar-type stars may in the not-too-distant
future be used to constrain certain properties of the stars. The C-D
diagram of large versus small frequency separations is one of the
powerful tools available to infer the properties - including perhaps
masses and ages - of stars which display a detectable spectrum of
oscillation. Also, the border of a convective region in a solar-type
star gives rise to a characteristic periodic signal in the star's
low-degree p-mode frequencies. Such a signature contains information
about the location and nature of the transition between convective and
non-convective regions in the star. In this work we address some of
the uncertainties associated with the direct use of the C-D diagram to
evaluate the mass and age of the star due to the unknown contributions
that make the stars different from the evolutionary models used to
construct our reference grid. We also explore the possibility of
combining an amplitude versus period diagram with the C-D diagram to
evaluate the properties of convective borders within solar-type stars.
---------------------------------------------------------
Title: MONS on the Danish Rømer satellite: measuring oscillations
in nearby stars
Authors: Christensen-Dalsgaard, J.
2002ESASP.485...25C Altcode: 2002sshp.conf...25C; 2001astro.ph.10444C
MONS (for Measuring Oscillations in Nearby Stars) is the scientific
project on the Danish Rømer satellite mission, which is being developed
as part of the Danish Small Satellite Programme. The principal goal
is to study solar-like oscillations in around 20 bright stars, with a
precision that in the best cases will be limited only by the intrinsic
stellar "noise". The baseline orbit, a so-called Molniya orbit,
allows access to essentially the entire sky during the planned 2-year
mission. The main instrument is a short-focus reflecting telescope with
an aperture of 32 cm, making two-colour measurements. A focused Field
Monitor will be used to detect and correct for possible faint variable
stars of substantial amplitude near the main target. In addition the
Field Monitor, and the Star Trackers on the platform, may be used to
observe a broad range of variable phenomena. The project has concluded
the Systems Definition Phase by a successful review, and launch is
scheduled for the middle of 2005.
---------------------------------------------------------
Title: Stellar Evolution
Authors: Christensen-Dalsgaard, J.
2002eaa..bookE1879C Altcode:
Stars evolve because they lose energy through radiation from their
hot surfaces. As a result, there is a general tendency for the star to
contract under gravity. This is partly stopped by the release of energy
from nuclear reactions. However, once the nuclear fuel is exhausted,
gravity gets the upper hand and the star ends its life as a compact
object: a white dwarf, a neutron star or a black hol...
---------------------------------------------------------
Title: Applications of Non-Adiabatic Radial Pulsation Equations to
roAp Stars
Authors: Medupe, R.; Christensen-Dalsgaard, J.; Kurtz, D. W.
2002ASPC..259..296M Altcode: 2002IAUCo.185..296M; 2002rnpp.conf..296M
No abstract at ADS
---------------------------------------------------------
Title: An Attempt at Mode Identification for V480 Tau
Authors: Di Mauro, M. P.; Christensen-Dalsgaard, J.; Pijpers, F.;
Hao, J.
2002ASPC..259..336D Altcode: 2002IAUCo.185..336D; 2002rnpp.conf..336D
Spectroscopic observations of the delta Scuti star V480 Tau, obtained
during the MUSICOS 1996 campaign (Hao et al. 2001), detected a large
number of modes. In order to assess the information available from
such data, we compare the observed spectrum of frequencies with the
theoretical predictions obtained for models computed by including the
effect of fast rotation on global oscillations.
---------------------------------------------------------
Title: Solar-like Oscillations of Semiregular Variables
Authors: Christensen-Dalsgaard, J.; Kjeldsen, H.; Mattei, J. A.
2001ApJ...562L.141C Altcode: 2001astro.ph.10475C
Oscillations of the Sun and solar-like stars are believed to be excited
stochastically by convection near the stellar surface. Theoretical
modeling predicts that the resulting amplitude increases rapidly
with the luminosity of the star. Thus, one might expect oscillations
of substantial amplitudes in red giants with high luminosities and
vigorous convection. Here we present evidence that such oscillations
may in fact have been detected in the so-called semiregular variables,
extensive observations of which have been made by amateur astronomers
in the American Association for Variable Star Observers. This may offer
a new opportunity for studying the physical processes that give rise
to the oscillations, possibly leading to further information about
the properties of convection in these stars.
---------------------------------------------------------
Title: Rotation of the solar interior
Authors: Christensen-Dalsgaard, J.; Thompson, M. J.
2001astro.ph.10607C Altcode:
Helioseismology has allowed us to infer the rotation in the greater part
of the solar interior with high precision and resolution. The results
show interesting conflicts with earlier theoretical expectations,
indicating that the the Sun is host to complex dynamical phenomena,
so far hardly understood. This has important consequences for our
ideas about the evolution of stellar rotation, as well as for models
for the generation of the solar magnetic field. Here we provide an
overview of our current knowledge about solar rotation, much of it
obtained from observations from the SOHO spacecraft, and discuss the
broader implications.
---------------------------------------------------------
Title: Changes in convective properties over the solar cycle: effect
on p-mode damping rates
Authors: Houdek, G.; Chaplin, W. J.; Appourchaux, T.;
Christensen-Dalsgaard, J.; Däppen, W.; Elsworth, Y.; Gough, D. O.;
Isaak, G. R.; New, R.; Rabello-Soares, M. C.
2001MNRAS.327..483H Altcode:
Measurements of both solar irradiance and p-mode oscillation
frequencies indicate that the structure of the Sun changes with
the solar cycle. Balmforth, Gough & Merryfield investigated the
effect of symmetrical thermal disturbances on the solar structure
and the resulting pulsation frequency changes. They concluded that
thermal perturbations alone cannot account for the variations in both
irradiance and p-mode frequencies, and that the presence of a magnetic
field affecting acoustical propagation is the most likely explanation
of the frequency change, in the manner suggested earlier by Gough &
Thompson and by Goldreich et al. Numerical simulations of Boussinesq
convection in a magnetic field have shown that at high Rayleigh number
the magnetic field can modify the preferred horizontal length scale
of the convective flow. Here, we investigate the effect of changing
the horizontal length scale of convective eddies on the linewidths
of the acoustic resonant mode peaks observed in helioseismic power
spectra. The turbulent fluxes in these model computations are obtained
from a time-dependent, non-local generalization of the mixing-length
formalism. The modelled variations are compared with p-mode linewidth
changes revealed by the analysis of helioseismic data collected by
the Birmingham Solar-Oscillations Network (BiSON); these low-degree
(low-l) observations cover the complete falling phase of solar activity
cycle 22. The results are also discussed in the light of observations
of solar-cycle variations of the horizontal size of granules and with
results from 2D simulations by Steffen of convective granules.
---------------------------------------------------------
Title: On the dipolar f mode of stellar oscillation
Authors: Christensen-Dalsgaard, J.; Gough, D. O.
2001MNRAS.326.1115C Altcode:
The classification of adiabatic modes of non-radial stellar oscillation
was established by Cowling in 1941. In addition to acoustic and
gravity modes he identified an intermediate mode, which he labelled
the f mode, and which in simple stellar models has no radial node. The
motion of a dipolar f mode (of spherical-harmonic degree l=1) shifts
the centre of mass, and must have zero frequency. On the other hand,
if the perturbation to the gravitational potential is neglected (the
case considered by Cowling) the f mode has a frequency intermediate
between those of the gravity and acoustic modes; this is true of
modes of any degree (l>=1). Here we consider the properties of the
dipolar f mode, elucidating the origin of these differences through
continuous transformations between the various relevant cases; in
addition, we discuss the broader issues of the classification of modes
of non-radial oscillation.
---------------------------------------------------------
Title: Solar Neutrino Emission Deduced from a Seismic Model
Authors: Turck-Chièze, S.; Couvidat, S.; Kosovichev, A. G.; Gabriel,
A. H.; Berthomieu, G.; Brun, A. S.; Christensen-Dalsgaard, J.; García,
R. A.; Gough, D. O.; Provost, J.; Roca-Cortes, T.; Roxburgh, I. W.;
Ulrich, R. K.
2001ApJ...555L..69T Altcode:
Three helioseismic instruments on the Solar and Heliospheric Observatory
have observed the Sun almost continuously since early 1996. This
has led to detailed study of the biases induced by the instruments
that measure intensity or Doppler velocity variation. Photospheric
turbulence hardly influences the tiny signature of conditions in the
energy-generating core in the low-order modes, which are therefore very
informative. We use sound-speed and density profiles inferred from GOLF
and MDI data including these modes, together with recent improvements
to stellar model computations, to build a spherically symmetric
seismically adjusted model in agreement with the observations. The
model is in hydrostatic and thermal balance and produces the present
observed luminosity. In constructing the model, we adopt the best
physics available, although we adjust some fundamental ingredients,
well within the commonly estimated errors, such as the p-p reaction
rate (+1%) and the heavy-element abundance (+3.5%); we also examine the
sensitivity of the density profile to the nuclear reaction rates. Then,
we deduce the corresponding emitted neutrino fluxes and consequently
demonstrate that it is unlikely that the deficit of the neutrino fluxes
measured on Earth can be explained by a spherically symmetric classical
model without neutrino flavor transitions. Finally, we discuss the
limitations of our results and future developments.
---------------------------------------------------------
Title: Imaging an Emerging Active Region with Helioseismic Tomography
Authors: Jensen, Jesper Munk; Duvall, Thomas L., Jr.; Jacobsen,
Bo Holm; Christensen-Dalsgaard, Jørgen
2001ApJ...553L.193J Altcode:
The wave-speed structure beneath an emerging active region is derived
from helioseismic time-distance data using inversion techniques
developed in geophysics. We use Fresnel zone-based sensitivity kernels
along with a Fourier domain-based regularized least-squares inversion
technique. The results show that wave-speed anomalies extend down to 20
Mm below active regions. We also see some evidence of deeper anomalies
that appear around 16-20 hr after the emergence of an active region
and then disappear within 8 hr. These anomalies could be the signature
of a change in the subsurface structure of the active region.
---------------------------------------------------------
Title: SX Phœnicis stars in the core of 47 Tucanae
Authors: Bruntt, H.; Frandsen, S.; Gilliland, R. L.;
Christensen-Dalsgaard, J.; Petersen, J. O.; Guhathakurta, P.; Edmonds,
P. D.; Bono, G.
2001A&A...371..614B Altcode: 2001astro.ph..4178B
We present new results on five of six known SX Phœnicis stars in the
core of the globular cluster 47 Tucanae. We give interpretations of
the light curves in the V and I bands from 8.3 days of observations
with the Hubble Space Telescope near the core of 47 Tuc. The most
evolved SX Phe star in the cluster is a double-mode pulsator (V2)
and we determine its mass to be (1.54+/-0.05) M<SUB>sun</SUB> from its
position in the Hertzsprung-Russell diagram and by comparing observed
periods with current theoretical pulsation models. For V14 we do not
detect any pulsation signal. For the double-mode pulsators V3, V15, and
V16 we cannot give a safe identification of the modes. We also describe
the photometric techniques we have used to extract the light curves
of stars in the crowded core. Some of the SX Phœnicis are saturated
and we demonstrate that even for stars that show signs of a bleeding
signal we can obtain a point-to-point accuracy of 1-3%. Based on
observations made with the NASA/ESA Hubble Space Telescope, obtained
at the Space Telescope Science Institute, which is operated by the
Association of Universities for Research in Astronomy Inc., under NASA
contract NAS5-26555.
---------------------------------------------------------
Title: Comparing Global Solar Rotation Results from MDI and GONG
Authors: Howe, R.; Komm, R. W.; Hill, F.; Christensen-Dalsgaard, J.;
Schou, J.; Thompson, M. J.; Corbard, T.
2001AGUSM..SP31A14H Altcode:
The GONG (Global Oscillations Network Group) project and the Solar
Oscillations Investigation (SOI) using the Michelson Doppler Imager
(MDI) instrument aboard the SOHO spacecraft have jointly accumulated
more than five years of data on medium-degree solar p-modes, including
nearly four years of contemporaneous observations. The inferences of
interior solar rotation from the two projects are broadly consistent
and show similar temporal variations, but there are also significant
systematic differences. We report here on the results of an ongoing
attempt to cross-compare the results and analysis techniques of the
two projects. Three 108-day periods, at low, medium and high solar
activity epochs, have been analysed, with both MDI and GONG analysis
being applied to each data set, and the results are compared.
---------------------------------------------------------
Title: Inversion of Time-Distance Data Using Non-ray-Theoretical
Sensitivity Kernels
Authors: Jensen, J. M.; Duvall, T. L.; Jacobsen, B. H.; Pijpers,
F. P.; Christensen-Dalsgaard, J.
2001AGUSM..SP31A23J Altcode:
Inversions of Helioseismic Time-Distance data present unique views of
the three-dimensional wave-speed variations in the solar interior. It
has e.g. become possible to image the subsurface wave-speed structures
beneath active regions and thus explore the magnetic activity of the
sun in a new way. Since the solar oscillations have long wavelengths
compared to the spatial extent of the features we wish to investigate,
the ray approximation is inadequate in such imaging. We present
inversions of Helioseismic Time-Distance data using non-ray-theoretical
sensitivity kernels. The kernels are obtained using the Rytov
approximation and have the so-called banana-doughnut shape. They are
zero along the raypath and most of the sensitivity is located in an
area corresponding to the first Fresnel zone around the ray. For the
inversion we use a Fourier-domain based regularized least-squares
method. We present results obtained using this inversion procedure,
along with averaging kernels and error estimates of the results. We
also present first results obtained using a SOLA inversion algorithm.
---------------------------------------------------------
Title: Variations in Rotation Rate Within the Solar Convection Zone
From GONG and MDI 1995-2000
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.;
Schou, J.; Thompson, M. J.; Toomre, J.
2001AGUSM..SP31A15H Altcode:
Helioseismic measurements with the Michelson Doppler Imager (MDI)
instrument aboard SOHO, and complementary measurements from the Global
Oscillation Network Group (GONG) project, are revealing changes deep
within the Sun as the solar cycle progresses. We will present the
latest results based on recent data from both experiments, including
flows in the upper part of the convection zone and variations in the
rotation rate near its base.
---------------------------------------------------------
Title: Seismology of solar-type stars
Authors: Basu, S.; Christensen-Dalsgaard, J.; Monteiro, M. J. P. F. G.;
Thompson, M. J.
2001ESASP.464..407B Altcode: 2001soho...10..407B
Seismology of solar-type stars other than the Sun becomes a realistic
possibly with the upcoming MOST, COROT and MONS missions, and the
ESA mission Eddington. We report on the results of experiments with
artificial data from models of solar-type stars to assess further what
we might learn about the internal structure of such stars.
---------------------------------------------------------
Title: Non-ideal effects on the solar equation of state
Authors: Bi, S. L.; di Mauro, M. P.; Christensen-Dalsgaard, J.
2001ESASP.464..499B Altcode: 2001soho...10..499B
This paper presents a simple and efficient equation of state which
can be used for quick and accurate computation of the thermodynamic
functions of partly ionized and weakly coupled plasmas (Bi, Di Mauro
and Christensen-Dalsgaard 2000). Based on the free energy minimization
method, the improvement of the equation of state includes a detailed
account of the physical processes of non-ideal effects consisting of
electron degeneracy, Coulomb coupling and pressure ionization. The
non-ideal corrections to the equation of state are calculated under
solar interior conditions. The result reveals that the contribution
is quite significant, and hence modifies the thermodynamic properties
of the plasma substantially.
---------------------------------------------------------
Title: Inversion for the solar internal rotation with an adaptive
regularization technique
Authors: Vorontsov, S. V.; Christensen-Dalsgaard, J.; Schou, J.;
Strakhov, V. N.; Thompson, M. J.
2001ESASP.464..559V Altcode: 2001soho...10..559V
We report the first preliminary results of applying the adaptive
regularization technique (Strakhov and Vorontsov 2000) to the inversion
for the solar internal rotation. The 360d SOHO MDI data set with 18-th
degree fit to the rotational splittings is used in the 1.5-D and 2-D
inversions, and we used the 72d data sets (Schou 1999) to trace the
possible variations with solar activity.
---------------------------------------------------------
Title: Comparing mode frequencies from MDI and GONG
Authors: Howe, R.; Hill, F.; Basu, S.; Christensen-Dalsgaard, J.;
Komm, R. W.; Munk Larsen, R.; Roth, M.; Schou, J.; Thompson, M. J.;
Toomre, J.
2001ESASP.464..137H Altcode: 2001soho...10..137H
We present results of analyses of MDI and GONG time series covering
the same time intervals, and using both the MDI and GONG peakbagging
algorithms. We discuss some of the likely causes of differences between
the inferred frequencies and frequency splittings. In addition, we
consider the effect of these differences on the results of inversions
for the solar internal rotation and sound speed.
---------------------------------------------------------
Title: Solar cycle changes in convection zone dynamics from MDI and
GONG 1995 - 2000
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.;
Munk Larsen, R.; Schou, J.; Thompson, M. J.; Toomre, J.
2001ESASP.464...19H Altcode: 2001soho...10...19H
The combined GONG and MDI medium-degree helioseismic data sets now cover
just over 5 years and allow us to probe the changing dynamics of the
convection zone in unprecedented detail. Here we present the latest
results from both projects, showing the evolution of the migrating
zonal flows close to the surface and also changes close to and below
the base of the convection zone.
---------------------------------------------------------
Title: Convective overshooting in the evolution and seismology of
η Bootis
Authors: di Mauro, M. P.; Christensen-Dalsgaard, J.
2001ESASP.464..373D Altcode: 2001soho...10..373D
In the near future frequencies of solar-like oscillations will
be observed by the several planned space missions, including MONS
(Measuring Oscillations in Nearby Stars), which will fly on board the
Danish Rømer satellite. In order to assess the information that will be
available from such observations, we consider theoretical predictions
of the frequency spectrum of oscillations of the star η Bootis, which
seems to show solar-type pulsations. We present results obtained by
comparing "classical" evolution models with models computed by taking
into account overshooting from the convective core.
---------------------------------------------------------
Title: Structure of Procyon A by a Seismological Approach
Authors: di Mauro, M. P.; Christensen-Dalsgaard, J.
2001IAUS..203...94D Altcode:
The success of helioseismology has spurred investigators to search
for similar oscillations in other Sun-like stars and extend this
diagnostic technique to become “asteroseismology”. In anticipation
of data that several planned space missions, including MONS satellite
(Measuring Oscillations in Nearby Stars), will be soon devoted to
provide, we consider the theoretical prediction of the power spectrum
of oscillations of Procyon A, which shows solar-type pulsations,
comparing models computed by taking into account an overshooting
from the convective core, as well as a diffusion of helium and
heavy-elements. We also calculate the frequency modification due
to a given internal rotational behaviour, in order to examine the
potential of asteroseismology to recognize, and with which accuracy,
the possible signature of differential rotation.
---------------------------------------------------------
Title: Recent Progress in Asteroseismology
Authors: Christensen-Dalsgaard, J.
2001IAUS..203...50C Altcode:
Asteroseismology, the study of stellar interiors on the basis of
observations of multi-mode stellar oscillations, extends over a large
part of the Hertzsprung-Russell diagram. Extensive observational
results have been obtained for δ Scuti stars, although the lack of
reliable mode identifications has so far precluded the use of the data
for detailed investigations. The recently discovered EC14026 stars (or
pulsating subdwarf B stars) promise information about the properties
of stars on the horizontal branch. Solar-like oscillations, i.e.,
oscillations excited stochastically by convection, have been tentatively
identified in a few cases, including through observations from the
WIRE satellite. Promising cases are giant stars, where the expected
amplitudes may make ground-based observations of the oscillations
relatively straightforward. Major advances can be expected from the
upcoming asteroseismic space projects under development or study;
the most ambitious of the latter is the Eddington mission, recently
proposed to ESA and up for selection later this year.
---------------------------------------------------------
Title: New Inferences on the Sun from High-degree Modes: the External
Layers and the Equation of State
Authors: di Mauro, M. P.; Christensen-Dalsgaard, J.
2001IAUS..203..177D Altcode:
We investigate the structure of the Sun by helioseismic inversion of
a set of p-mode frequencies which include new accurate observations
of modes with high degree (l < 1000) obtained from MDI instrument
flying on board of SOHO satellite. The use of high-degree frequencies
highly improves the resolution of the solar structure in the
near-surface region, where effects of the equation of state are felt
more strongly. In particular, we show the potential of such data to
test the solar equation of state and to constrain the solar envelope
helium abundance.
---------------------------------------------------------
Title: Interior Solar-Cycle Changes Detected by Helioseismology
Authors: Howe, R.; Hill, F.; Komm, R. W.; Christensen-Dalsgaard, J.;
Munk Larsen, R.; Schou, J.; Thompson, M. J.; Toomre, J.
2001IAUS..203...40H Altcode:
Helioseismic measurements with the MDI instrument aboard SOHO,
and complementary measurements from the GONG network, are revealing
changes deep within the Sun as the solar cycle progresses. We will
present results based on recent data from both experiments, including
variations in the rotation rate deep inside the convection zone.
---------------------------------------------------------
Title: On the signature of the solar activity at the base of the
convective envelope
Authors: Monteiro, M. J. P. F. G.; Christensen-Dalsgaard, J.; Schou,
J.; Thompson, M. J.
2001ESASP.464..535M Altcode: 2001soho...10..535M
A we approach the solar maximum for the current cycle it is timely to
establish what helioseismology can tell us about the internal changes
the Sun undergoes as the cycle progresses. In this work we use SOI-MDI
data in order to identify changes occurring to the stratification of
the Sun at the base of the convective envelope. Both changes with
time (averaged over colatitude) and changes over time at different
colatitudes are addressed. These are discussed in terms of the changes
in the properties of the convection at the base of the envelope in
the region where the tachocline is present. Those variations could
be attributed to the interaction between convection, rotation and
magnetic fields, which must be intrinsically time-dependent phenomena,
possibly correlated with the observed changes occurring over the cycle
in the envelope up to the surface.
---------------------------------------------------------
Title: Coulomb corrections to the equation of state for a
weakly-coupled plasma
Authors: Bi, S. L.; Di Mauro, M. P.; Christensen-Dalsgaard, J.
2000A&A...364..157B Altcode:
Coulomb corrections to the equation of state of degenerate matter
are usually described by Debye-Hückel theory; however, recent
studies have considered modifications of thermodynamic quantities
which are caused by the interactions of charged particles beyond the
Debye-Hückel approximation. Based on the weakly-coupled plasma limit,
the formulae for the physical properties of non-ideal effects on the
equation of state are derived. The treatment of the non-ideal effects
due to Coulomb coupling combines the results of quantum-statistic
calculations for the electrons, N-body semianalytic theory for ions,
and the extended Debye-Hückel theory with hard-core correction for
the electron-ion interaction. The leading Coulomb correction not only
can be applied to the weak-coupling region, but also preserves the
well-known Debye-Hückel limit at Gamma << 1. We examine the
Coulomb correction to the thermodynamic quantities of a weakly coupled
and fully ionized plasma. The result reveals that the contribution is
quite significant, and hence modifies the thermodynamic properties of
the plasma substantially.
---------------------------------------------------------
Title: An improved equation of state under solar interior conditions
Authors: Bi, S. L.; Di Mauro, M. P.; Christensen-Dalsgaard, J.
2000A&A...364..879B Altcode:
This paper presents a simple and efficient equation of state which
can be used for quick and accurate computing of the thermodynamic
functions of partly ionized and weakly coupled plasmas. Based on the
free energy minimization method, the improvement of the equation
of state includes a detailed account of the physical processes of
non-ideal effects consisting of electron degeneracy, Coulomb coupling
and pressure ionization. The treatment of Coulomb coupling combines
the results of the quantum exchange effect of degenerate electrons
at finite temperature, N-body semi-analytic theory and the extended
Debye-Hückel theory with hard-sphere correction. For the complicated
physical processes of pressure ionization an approximate model is
adopted. The nonideal corrections to equation of state are calculated
under solar interior conditions.
---------------------------------------------------------
Title: Helioseismology: Theory
Authors: Christensen-Dalsgaard, J.
2000eaa..bookE2249C Altcode:
Observations have shown that the solar surface is in a state of
continual oscillation, involving a very large number of different
modes (see HELIOSEISMIC OBSERVATIONS). The observed frequencies depend
in a relatively simple manner on the structure and rotation of the
solar interior. To use this information to probe the Sun we need to
understand how the properties of the oscillations reflect cond...
---------------------------------------------------------
Title: Nuclei in the Cosmos 2000
Authors: Christensen-Dalsgaard, Jørgen; Langanke, Karlheinz
2000PASP..112.1514C Altcode:
Conference was held in Århus, Denmark, in 2000 June. Proceedings will
be edited by J. Christensen-Dalsgaard and K. Langanke and published
as a regular volume in Nuclear Physics A.
---------------------------------------------------------
Title: The effect of diffusion on pulsations of stars on the upper
main sequence --- δ Scuti and metallic A stars
Authors: Turcotte, S.; Richer, J.; Michaud, G.; Christensen-Dalsgaard,
J.
2000A&A...360..603T Altcode: 2000astro.ph..6272T
Recent dramatic improvements in the modeling of abundance evolution
due to diffusion in A stars have been achieved with the help of
monochromatic opacity tables from the OPAL group. An important result
in the context of stellar pulsations is the substantial helium abundance
shown to be left over in the driving region of δ Scuti-type pulsations
in chemically peculiar Am stars. An accurate opacity profile in the
entire stellar envelope including the full effect of heavy elements
is also now available for the first time. Pulsations are shown to
be excluded for young Am stars but occur naturally when these stars
evolve off the ZAMS. The predicted variable metallic A stars all lie
towards the red edge of the instability strip, in qualitative agreement
with the observed variable δ Delphini and mild Am stars. Results show
little direct excitation from iron-peak elements in A-type stars. The
main abundance effect is due to the settling of helium, along with a
marginal effect due to the enhancement of hydrogen.
---------------------------------------------------------
Title: Seismic study of stellar convective regions: the base of the
convective envelope in low-mass stars
Authors: Monteiro, Mário J. P. F. G.; Christensen-Dalsgaard, Jørgen;
Thompson, Michael J.
2000MNRAS.316..165M Altcode:
The possibility of observing solar-type oscillations on other stars
is of great relevance to investigating the uncertain aspects of the
internal structure of stars. One of these aspects is the convective
overshoot that takes place at the borders of the envelopes of
stars of mass similar to, or lower than, the Sun. It affects the
temperature stratification, mixing, rotation and magnetic-field
generation. Asteroseismology can provide an observational test for the
studies of the structure of such overshoot regions. The seismic study of
the transition in the Sun, located at the base of the convection zone,
has been successful in determining the characteristics of this layer
in the Sun. In this work we consider the extension of the analysis to
other solar-type stars (of mass between 0.85 and 1.2M<SUB>solar</SUB>)
in order to establish a method for determining the characteristics
of their convective envelopes. In particular, we hope to be able to
establish seismologically that a star does indeed possess a convective
envelope, to measure the size of the convective region and also to
constrain the properties of an overshoot layer at the bottom of the
envelope. The limitations in terms of observational uncertainties and
stellar characteristics, and the detectability of an overshoot layer,
are discussed.
---------------------------------------------------------
Title: Structure of the Solar Core: Effect of Asymmetry of Peak
Profiles
Authors: Basu, S.; Turck-Chièze, S.; Berthomieu, G.; Brun, A. S.;
Corbard, T.; Gonczi, G.; Christensen-Dalsgaard, J.; Provost, J.;
Thiery, S.; Gabriel, A. H.; Boumier, P.
2000ApJ...535.1078B Altcode: 2000astro.ph..1208B
Recent studies have established that peaks in solar oscillation
power spectra are not Lorentzian in shape but have a distinct
asymmetry. Fitting a symmetric Lorentzian profile to the peaks,
therefore, produces a shift in frequency of the modes. Accurate
determination of low-frequency modes is essential to infer the structure
of the solar core by inversion of the mode frequencies. In this paper
we investigate how the changes in frequencies of low-degree modes
obtained by fitting symmetric and asymmetric peak profiles change the
inferred properties of the solar core. We use data obtained by the
Global Oscillations at Low Frequencies (GOLF) project on board the
SOHO spacecraft. Two different solar models and inversion procedures
are used to invert the data in order to determine the sound speed in
the solar core. We find that for a given set of modes no significant
difference in the inferred sound speed results from taking asymmetry
into account when fitting the low-degree modes.
---------------------------------------------------------
Title: Solar-Cycle Changes in Convection-Zone Dynamics from SOI and
GONG Data
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.;
Larsen, R. M.; Schou, J.; Thompson, M. J.; Toomre, J.
2000SPD....31.0113H Altcode: 2000BAAS...32..803H
The combined GONG and MDI medium-degree helioseismic data sets now cover
more than 4.5 years and allow us to probe the changing dynamics of the
convection zone in unprecedented detail. Here we present the latest
results from both projects, showing the evolution of the migrating zonal
flows close to the surface and also changes close to and below the base
of the convection zone. This work utilizes data obtained by the Global
Oscillation Network Group (GONG) project, managed by the National Solar
Observatory, a Division of the National Optical Astronomy Observatories,
which is operated by AURA, Inc. under a cooperative agreement with the
National Science Foundation. SOHO is a joint project of ESA and NASA.
---------------------------------------------------------
Title: The potential of solar high-degree modes for structure
inversion
Authors: Rabello-Soares, M. C.; Basu, Sarbani; Christensen-Dalsgaard,
J.; Di Mauro, M. P.
2000SoPh..193..345R Altcode:
It is likely that precise and reliable frequencies of high-degree modes
will soon be available from the SOI/MDI experiment. Here we examine the
ability of such modes (with l>300) to resolve the solar structure
in the near-surface region. In particular, we investigate inversions
to determine the adiabatic exponent Γ<SUB>1</SUB> as a test of the
solar equation of state, as well as the potential of such data to
constrain the solar envelope helium abundance.
---------------------------------------------------------
Title: US Mission of Opportunity on MONS
Authors: Schou, J.; Scherrer, P. H.; Bogart, R. S.;
Christensen-Dalsgaard, J.; Kjeldsen, H.; Buzasi, D. L.
2000mons.proc..123S Altcode:
The Measuring Oscillations in Nearby Stars (MONS) Survey Telescope
(MONS-ST) is a Mission of Opportunity that will study the interior
of a large number of stars using stellar oscillations. MONS-ST will
provide additional hardware and/or extend the lifetime of the Danish
MONS micro satellite, which has been selected for flight in 2003. The
additional hardware provided by MONS-ST will enhance the MONS mission
by increasing the number of stars observable and extending the lifetime
of the mission. A Guest Investigator program, allowing a number of
scientists to propose targets and analyze data, will be part of the
mission.
---------------------------------------------------------
Title: Deeply Penetrating Banded Zonal Flows in the Solar Convection
Zone
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.;
Larsen, R. M.; Schou, J.; Thompson, M. J.; Toomre, J.
2000ApJ...533L.163H Altcode: 2000astro.ph..3121H
Helioseismic observations have detected small temporal variations
of the rotation rate below the solar surface that correspond to the
so-called “torsional oscillations” known from Doppler measurements of
the surface. These appear as bands of slower- and faster-than-average
rotation moving equatorward. Here we establish, using complementary
helioseismic observations over 4 yr from the GONG network and from
the MDI instrument on board SOHO, that the banded flows are not
merely a near-surface phenomenon: rather, they extend downward at
least 60 Mm (some 8% of the total solar radius) and thus are evident
over a significant fraction of the nearly 200 Mm depth of the solar
convection zone.
---------------------------------------------------------
Title: Eddington: a proposal to ESA for asteroseismology and
planet-finding
Authors: Favata, F.; Roxburgh, I.; Christensen-Dalsgaard, J.
2000mons.proc...49F Altcode:
Eddington is a proposal to the European Space Agency (ESA) for a
moderate-size (d~= 1.2 m), wide-field (Ω >= 6 sq. deg) optical
telescope, which will be used for asteroseismic investigations as well
as for extra-solar planet finding. The mission has been proposed to
ESA in the framework of the F2/F3 mission opportunity and has recently
been selected for a study, with a final selection due in September
2000. This paper briefly describes the proposed mission, as well as
the current study baseline and organization.
---------------------------------------------------------
Title: Evolution, Seismology and Internal Dynamics of Procyon
Authors: di Mauro, M. P.; Christensen-Dalsgaard, J.; Weiss, A.
2000mons.proc..151D Altcode:
We consider the theoretical prediction of the power spectrum of
oscillations of Procyon A which shows solar-like pulsations. We also
calculate the frequency modification due to a given internal rotational
behaviour, in order to examine the potential of asteroseismology
to recognize, and with which accuracy, the possible signature of
differential rotation.
---------------------------------------------------------
Title: Time Variability of Rotation in Solar Convection Zone From
soi-mdi
Authors: Toomre, J.; Christensen-Dalsgaard, J.; Howe, R.; Larsen,
R. M.; Schou, J.; Thompson, M. J.
2000SoPh..192..437T Altcode:
The variation of rotation in the convection zone over a period of two
years from mid-1996 is studied using inversions of SOI-MDI data. We
confirm the existence of near-surface banded zonal flows migrating
towards the equator from higher latitudes, and reveal that these banded
flows extend substantially beneath the surface, possibly to depths
as great as 70 Mm (10% of the solar radius). Our results also reveal
apparently significant temporal variations in the rotation rate at
high latitudes and in the vicinity of the tachocline over the period
of study.
---------------------------------------------------------
Title: Dynamic Variations at the Base of the Solar Convection Zone
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.;
Larsen, R. M.; Schou, J.; Thompson, M. J.; Toomre, J.
2000Sci...287.2456H Altcode:
We have detected changes in the rotation of the sun near the base of
its convective envelope, including a prominent variation with a period
of 1.3 years at low latitudes. Such helioseismic probing of the deep
solar interior has been enabled by nearly continuous observation of
its oscillation modes with two complementary experiments. Inversion of
the global-mode frequency splittings reveals that the largest temporal
changes in the angular velocity Ω are of the order of 6 nanohertz
and occur above and below the tachocline that separates the sun's
differentially rotating convection zone (outer 30% by radius) from
the nearly uniformly rotating deeper radiative interior beneath. Such
changes are most pronounced near the equator and at high latitudes and
are a substantial fraction of the average 30-nanohertz difference in Ω
with radius across the tachocline at the equator. The results indicate
variations of rotation close to the presumed site of the solar dynamo,
which may generate the 22-year cycles of magnetic activity.
---------------------------------------------------------
Title: Sensitivity Kernels for Time-Distance Inversion
Authors: Jensen, Jesper Munk; Jacobsen, Bo Holm; Christensen-Dalsgaard,
Jørgen
2000SoPh..192..231J Altcode:
Inversion of local-area helioseismic time-distance data has so far only
been done in the ray approximation (Kosovichev, 1996). Since this is
a high-frequency approximation its applicability can be questioned
for the solar case. Bogdan (1997) showed that for a simple solar
model the localized wave packets do follow, but are not confined to,
the ray path. We use an approximation based on the first Fresnel
zone that has been developed in geophysics by Snieder and Lomax
(1996) to go beyond the ray approximation in the inversions. We
have calculated sensitivity kernels using both approximations. To
test them we use a finite-difference forward modeling of the whole
wave field in an acoustic medium reminiscent of the Sun. We use the
finite-difference modeling to calculate sensitivity kernels for the
full wave field and compare this with the other kernels. The results
show that the Fresnel-zone-based kernels are in good agreement with the
sensitivity obtained from the modeling. Thus these new kernels represent
a significant step forward in the inversion of time-distance data.
---------------------------------------------------------
Title: MONS: Measuring Oscillations in Nearby Stars
Authors: Kjeldsen, H.; Bedding, T. R.; Christensen-Dalsgaard, J.
2000ASPC..203...73K Altcode: 2000ilss.conf...73K; 2000IAUCo.176...73K
Asteroseismology on δ Scuti stars has until now produced very few
convincing results -- if we aim at doing strong tests of details of
stellar modelling. The main reason for the lack of success is probably
that these stars often rotate, which split nonradial oscillation
frequencies into many more frequencies. These many frequencies and the
fact that the more evolved δ Scuti stars contain a strong chemical
composition gradient at the edge of the convective core, produce a very
complicated eigenfrequency spectrum. In contrast to this, we expect, in
principle, seismological studies of δ Scuti stars to be a very simple
task: One has to compare theoretical oscillations in model stars with
the observed oscillations. However, in order to produce convincing
asteroseismological results, we need to do three things: (1) Detect
as many eigenfrequencies as possible at high precision, (2) identify
the eigenmodes and (3) improve the theoretical models. By observing
δ Scuti stars in open clusters using CCDs, we have a possibility
to improve on (1) and (2) as well as providing an opening for an
improvement in the theoretical models by doing accurate calibrations
of the basic cluster properties. In this paper I shall describe some
of the results from CCD studies of δ Scuti stars in open clusters
and identify some future prospects for this technique.
---------------------------------------------------------
Title: Studies of Non-adiabatic Effects on Radial Pulsations in the
Atmospheres of Rapidly Oscillating Ap Stars
Authors: Medupe, R.; Kurtz, D. W.; Christensen-Dalsgaard, J.
2000ASPC..203..451M Altcode: 2000ilss.conf..451M; 2000IAUCo.176..451M
A code for solving non-adiabatic radial pulsation equations with
consistent treatment of radiative transfer is used to study the
oscillations in the atmospheres of the rapidly oscillating Ap stars. We
find that our results are consistent with the presence of an observable
node in the temperature eigenfunction.
---------------------------------------------------------
Title: Implications of helioseismology for stellar structure and
evolution
Authors: Christensen-Dalsgaard, J.
2000ASPC..198...31C Altcode: 2000scac.conf...31C
No abstract at ADS
---------------------------------------------------------
Title: An Introduction to Helioseismology
Authors: Christensen-Dalsgaard, J.; Däppen, W.; Dziembowski, W. A.;
Guzik, J. A.
2000ASIC..544...59C Altcode: 2000vsea.conf...59C
No abstract at ADS
---------------------------------------------------------
Title: Basic Aspects of Stellar Structure and Pulsation
Authors: Christensen-Dalsgaard, J.; Dziembowski, W. A.
2000ASIC..544....1C Altcode: 2000vsea.conf....1C
No abstract at ADS
---------------------------------------------------------
Title: Commission 27: Variable Stars: (Les Etoiles Variables)
Authors: Kurtz, D. W.; Christensen-Dalsgaard, J.; Cacciari, C.;
Cottrell, P.; Harmanec, P.; Jerzykiewicz, M.; Matthews, J.; Moskalik,
P.; Sasselov, D.; Welch, D.
2000IAUTA..24..255K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An Introduction to the Theory of δ Scuti Stars
Authors: Christensen-Dalsgaard, J.
2000ASPC..210..187C Altcode: 2000dsrs.conf..187C
No abstract at ADS
---------------------------------------------------------
Title: Helioseismic detection of temporal variations of solar rotation
rate near the base of the convection zone
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.;
Larsen, R. M.; Schou, J.; Thompson, M. J.; Toomre, J.
1999AAS...19510702H Altcode: 1999BAAS...31R1530H
The differential rotation of the Sun and its ability to generate
large-scale magnetic fields through cyclic dynamo action appear to be
intimately linked. It is now commonly thought that the global dynamo
behavior responsible for the emergence of active regions is derived
from strong organized toroidal magnetic fields generated by rotational
shear in a thin region (the tachocline) at the base of the convection
zone. The magnetic field could well have a feedback effect on the fluid
motions in the region. We are thus motivated to use helioseismology
to look for changes in rotation profiles near the tachocline as the
Sun's magnetic cycle progresses. This approach has become possible
using frequency-splitting data for p- and f-mode oscillations derived
over four years (from May 1995 to Sept 1999) of full-disk Doppler
observations from the ground-based Global Oscillation Network Group
(GONG) project and from the Michelson Doppler Imager (MDI) experiment
aboard the SOHO spacecraft. Inversions using two different methods of
the splittings from these two independent data sets reveal systematic
variations of the rotation rate close to the base of the convection
zone, with different behavior at low and high latitudes. Notable
are variations of order 6 nHz in rotation rates near the equator,
to be compared with the radial angular velocity contrast across the
tachocline of about 30 nHz. These exhibit several nearly repetitive
changes with a period of about 1.2-1.4 years and appear to be real
changes in the deep convection zone and tachocline rotation rates that
need to be followed as the solar cycle progresses. The GONG project is
managed by the National Solar Observatory, a Division of the National
Optical Astronomy Observatories, which is operated by AURA, Inc. under
a cooperative agreement with the National Science Foundation. SOHO is
a joint project of ESA and NASA.
---------------------------------------------------------
Title: Helioseismic Constraints on the Structure of the Solar
Tachocline
Authors: Charbonneau, P.; Christensen-Dalsgaard, J.; Henning, R.;
Larsen, R. M.; Schou, J.; Thompson, M. J.; Tomczyk, S.
1999ApJ...527..445C Altcode:
This paper presents a series of helioseismic inversions aimed at
determining with the highest possible confidence and accuracy the
structure of the rotational shear layer (the tachocline) located
beneath the base of the solar convective envelope. We are particularly
interested in identifying features of the inversions that are robust
properties of the data, in the sense of not being overly influenced
by the choice of analysis methods. Toward this aim we carry out
two types of two-dimensional linear inversions, namely Regularized
Least-Squares (RLS) and Subtractive Optimally Localized Averages
(SOLA), the latter formulated in terms of either the rotation rate or
its radial gradient. We also perform nonlinear parametric least-squares
fits using a genetic algorithm-based forward modeling technique. The
sensitivity of each method is thoroughly tested on synthetic data. The
three methods are then used on the LOWL 2 yr frequency-splitting
data set. The tachocline is found to have an equatorial thickness
of w/R<SUB>solar</SUB>=0.039+/-0.013 and equatorial central radius
r<SUB>c</SUB>/R<SUB>solar</SUB>=0.693+/-0.002. All three techniques
also indicate that the tachocline is prolate, with a difference in
central radius Δr<SUB>c</SUB>/R<SUB>solar</SUB>~=0.024+/-0.004 between
latitude 60° and the equator. Assuming uncorrelated and normally
distributed errors, a strictly spherical tachocline can be rejected
at the 99% confidence level. No statistically significant variation
in tachocline thickness with latitude is found. Implications of these
results for hydrodynamical and magnetohydrodynamical models of the
solar tachocline are discussed.
---------------------------------------------------------
Title: Rotation of the solar interior
Authors: Christensen-Dalsgaard, Jørgen; Thompson, Michael J.
1999CSci...77.1460C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Pulsation models of delta Scuti variables. II. delta Scuti
stars as precise distance indicators
Authors: Petersen, J. O.; Christensen-Dalsgaard, J.
1999A&A...352..547P Altcode:
The Hipparcos period-luminosity relation for high-amplitude delta Scuti
stars is discussed as an average period-luminosity-colour-metallicity
relation comparing the Hipparcos sample of calibrating stars with a
more representative sample taken from McNamara (1997). The Hipparcos
relation includes systematic effects of both colour and metallicity
and agrees with other period-luminosity relations with an accuracy of
about +/- 0.10 mag. Direct stellar-evolution and pulsation modelling is
used to study effects on the average period-luminosity relation from
the location of the high-amplitude variables within the instability
strip given as a range in effective temperature (colour term) and the
metallicity given as [Fe/H]. Using accurate data for the instability
strip given by McNamara precise agreement with the Hipparcos relation is
found. By fitting the bolometric magnitude as a function of pulsation
period, effective temperature and metallicity an accuracy of 0.02-0.03
mag is obtained both within the narrow high-amplitude strip and
including a much broader strip covering most of the full {delta Sct}
instability strip. Problems in practical application of this relation
are briefly considered. Using uvbybeta narrow-band photometry it seems
possible to obtain this accuracy in determinations of distances to
e.g. the Galactic Bulge and the Magellanic Clouds.
---------------------------------------------------------
Title: Amplitudes of stochastically excited oscillations in
main-sequence stars
Authors: Houdek, G.; Balmforth, N. J.; Christensen-Dalsgaard, J.;
Gough, D. O.
1999A&A...351..582H Altcode: 1999astro.ph..9107H
We present estimates of the amplitudes of intrinsically stable
stochastically excited radial oscillations in stars near the
main sequence. The amplitudes are determined by the balance
between acoustical energy generation by turbulent convection (the
Lighthill mechanism) and linear damping. Convection is treated with
a time-dependent, nonlocal, mixing-length model, which includes both
convective heat flux and turbulent pressure in both the equilibrium
model and the pulsations. Velocity and luminosity amplitudes are
computed for stars with masses between 0.9 M_sun and 2.0 M_sun in the
vicinity of the main sequence, for various metallicities and convection
parameters. As in previous studies, the amplitudes are found to increase
with stellar mass, and therefore with luminosity. Amongst those stars
that are pulsationally stable, the largest amplitudes are predicted
for a 1.6 M_sun model of spectral type F2; the values are approximately
15 times larger than those measured in the Sun.
---------------------------------------------------------
Title: Convective contributions to the frequencies of solar
oscillations
Authors: Rosenthal, C. S.; Christensen-Dalsgaard, J.; Nordlund, Å.;
Stein, R. F.; Trampedach, R.
1999A&A...351..689R Altcode: 1998astro.ph..3206R
Differences between observed and theoretical eigenfrequencies of the Sun
have characteristics which identify them as arising predominantly from
properties of the oscillations in the vicinity of the solar surface:
in the super-adiabatic, convective boundary layer and above. These
frequency differences may therefore provide useful information about
the structure of these regions, precisely where the theory of solar
structure is most uncertain. In the present work we use numerical
simulations of the outer part of the Sun to quantify the influence
of turbulent convection on solar oscillation frequencies. Separating
the influence into effects on the mean model and effects on the
physics of the modes, we find that the main model effects are due
to the turbulent pressure that provides additional support against
gravity, and thermal differences between average 3-D models and 1-D
models. Surfaces of constant pressure in the visible photosphere are
elevated by about 150 km, relative to a standard envelope model. As a
result, the turning points of high-frequency modes are raised, while
those of the low-frequency modes remain essentially unaffected. The
corresponding gradual lowering of the mode frequencies accounts for
most of the frequency difference between observations and standard
solar models. Additional effects are expected to come primarily from
changes in the physics of the modes, in particular from the modulation
of the turbulent pressure by the oscillations.
---------------------------------------------------------
Title: Effects of line asymmetries on the determination of solar
internal structure
Authors: Rabello-Soares, M. C.; Christensen-Dalsgaard, J.; Rosenthal,
C. S.; Thompson, M. J.
1999A&A...350..672R Altcode: 1999astro.ph..8250R
Despite the strong evidence that the peaks in the spectrum of solar
oscillations are asymmetric, most determinations of mode frequencies
have been based on fits of symmetric Lorentzian profiles to the Fourier
or power spectra of oscillation time strings. The systematic errors
resulting from neglecting the line asymmetry could have serious effects
on inversions for the solar internal structure and rotation. Here we
analyse artificial data based on simple models of the intrinsic line
asymmetry, using GONG mode parameters with asymmetries found by one
of us (Rosenthal \cite{rosenthal2}). By fitting Lorentzians to the
resulting spectra, we estimate the likely properties of the errors
introduced in the frequencies. We discuss whether these frequency
shifts have a form similar to the near-surface layers uncertainties
and are therefore suppressed in the solar structure inversion. We also
estimate directly their contribution, if any, in the solar sound-speed
and density determinations using the SOLA technique.
---------------------------------------------------------
Title: A note on Saio's estimate of second-order effects of rotation
on stellar oscillation frequencies
Authors: Christensen-Dalsgaard, J.; Thompson, M. J.
1999A&A...350..852C Altcode:
In many cases, oscillating stars rotate so rapidly that second-order
effects must be taken into account in analyses of the oscillation
frequencies. Such investigations have commonly been based on results
provided by Saio (1981) for a polytropic model. Here we compare those
with frequency changes for more realistic models; we point out that
a simple correction to Saio's data allows them to be used in the
observationally relevant case of comparing models at fixed luminosity
and effective temperature.
---------------------------------------------------------
Title: On the choice of parameters in solar-structure inversion
Authors: Rabello-Soares, M. C.; Basu, Sarbani; Christensen-Dalsgaard,
J.
1999MNRAS.309...35R Altcode: 1999astro.ph..5107R
The observed solar p-mode frequencies provide a powerful diagnostic of
the internal structure of the Sun and permit us to test in considerable
detail the physics used in the theory of stellar structure. Among the
most commonly used techniques for inverting such helioseismic data
are two implementations of the optimally localized averages (OLA)
method, namely the subtractive optimally localized averages (SOLA) and
multiplicative optimally localized averages (MOLA). Both are controlled
by a number of parameters, the proper choice of which is very important
for a reliable inference of the solar internal structure. Here we make
a detailed analysis of the influence of each parameter on the solution
and indicate how to arrive at an optimal set of parameters for a given
data set.
---------------------------------------------------------
Title: Rotation of the solar core from BiSON and LOWL frequency
observations
Authors: Chaplin, W. J.; Christensen-Dalsgaard, J.; Elsworth, Y.;
Howe, R.; Isaak, G. R.; Larsen, R. M.; New, R.; Schou, J.; Thompson,
M. J.; Tomczyk, S.
1999MNRAS.308..405C Altcode:
Determination of the rotation of the solar core requires very accurate
data on splittings for the low-degree modes which penetrate to the core,
as well as for modes of higher degree to suppress the contributions
from the rest of the Sun to the splittings of the low-degree modes. Here
we combine low-degree data based on 32 months of observations with the
BiSON network and data from the LOWL instrument. The data are analysed
with a technique that specifically aims at obtaining an inference of
rotation that is localized to the core. Our analysis provides what we
believe is the most stringent constraint to date on the rotation of
the deep solar interior.
---------------------------------------------------------
Title: Time-Variability of the Inferred Rotation in the Upper
Convection Zone
Authors: Toomre, J.; Christensen-Dalsgaard, J.; Howe, R.; Larsen,
R. M.; Schou, J.; Thompson, M. J.
1999soho....9E..87T Altcode:
We present results of inverting for the rotation of the upper convection
zone, using frequency splittings derived from successive 72-day time
series of SOI-MDI observations. Schou (1999; also Schou et al. 1998)
has studied the evolution of the pattern of small-scale zonal flows
in the near-surface layers using f-mode splittings and has found that
this flow pattern migrates equatorward in a manner similar to that seen
in the so-called torsional oscillation observed in surface Doppler
measurements. In the present work we look at the time variability
of the rotation at greater depth, in the upper convection zone, by
inverting both f- and p-mode splittings. The evolution of the flow is
less regular than is seen at the surface, but we do observe apparently
significant variations in the inferred flow pattern, on latitudinal
scales similar to those seen at the surface. In particular, in the
subsurface shear layer we see intriguing variations, with the first
year's data showing apparent emergence of zonal flows of some 10-15
m/s amplitude at around 20 degrees latitude.
---------------------------------------------------------
Title: Convective Envelopes in Solar-Type Stars: What Can We Learn
from their Seismic Study?
Authors: Monteiro, M. J. P. F. G.; Christensen-Dalsgaard, J.; Thompson,
M. J.
1999ASPC..173..273M Altcode: 1999sstt.conf..273M
No abstract at ADS
---------------------------------------------------------
Title: The Potential of Solar High-Degree Oscillation Frequencies
for Structure Inversion
Authors: Rabello-Soares, M. C.; Basu, Sarbani; Christensen-Dalsgaard,
J.; di Mauro, M. P.
1999soho....9E..78R Altcode:
It is likely that precise and reliable frequencies of high-degree modes
will soon be available from the SOI/MDI experiment. Here we examine the
ability of such modes (with l > 300) to resolve the solar structure
in the near-surface region. In particular, we investigate inversions to
determine the adiabatic exponent G1 (Basu & Christensen-Dalsgaard,
1997) as a test of the solar equation of state, as well as the potential
of such data to constrain the solar envelope helium abundance.
---------------------------------------------------------
Title: Probing Solar Convection with p-Mode Linewidths
Authors: Rabello-Soares, M. C.; Houdek, G.; Christensen-Dalsgaard, J.
1999ASPC..173..301R Altcode: 1999sstt.conf..301R
No abstract at ADS
---------------------------------------------------------
Title: On the Location of the Instability Strip
Authors: Houdek, G.; Balmforth, N. J.; Christensen-Dalsgaard, J.;
Gough, D. O.
1999ASPC..173..317H Altcode: 1999sstt.conf..317H
No abstract at ADS
---------------------------------------------------------
Title: Sensitivity Kernels for Time-Distance Inversion
Authors: Jensen, J. M.; Jacobsen, B. H.; Christensen-Dalsgaard, J.
1999soho....9E..67J Altcode:
Inversion of local area helioseismic Time-Distance data has so far only
been done in the ray approximation (Kosovichev 1996). Since this is a
high frequency approximation its applicability can be questioned for
the solar case. Bogdan (1997) showed that for a simple solar model
the sensitivity of the wavepackets do follow the raypath but is not
confined to the raypath. We use an approximation based on the first
Fresnel zone that has been developed in geophysics by Snieder and Lomax
(1996) to go beyond the ray approximation in the inversions. We have
calculated sensitivity kernels using both approximation. To test them
we used a finite difference forward modelling of the whole wave field
in an acoustic medium reminiscent of the sun to calculate synthetic
data. These data were inverted using both approximations. We also used
the finite difference modelling to calculate sensitivity kernels using
the full wave field and compared this to the other kernels. The results
show that the Fresnel-zone-based kernels are in good agreement with
the sensitivity obtained from the modelling, and also perform well in
the inversions. Thus these new kernels represent a significant step
forward in the inversion of Time-Distance data.
---------------------------------------------------------
Title: Stellar Evolution with a Variable Mixing-Length Parameter
Authors: Trampedach, R.; Stein, R. F.; Christensen-Dalsgaard, J.;
Nordlund, Å.
1999ASPC..173..233T Altcode: 1999sstt.conf..233T
No abstract at ADS
---------------------------------------------------------
Title: MONS: A Proposal for a Danish Satellite
Authors: Kjeldsen, H.; Bedding, T. R.; Frandsen, S.; dall, T. H.;
Thomsen, B.; Christensen-Dalsgaard, J.; Clausen, J. V.; Petersen,
J. O.; Andersen, M. I.
1999ASPC..173..353K Altcode: 1999sstt.conf..353K
No abstract at ADS
---------------------------------------------------------
Title: Probing Convection with Helio- and Asteroseismology
Authors: Christensen-Dalsgaard, J.
1999ASPC..173...51C Altcode: 1999sstt.conf...51C
No abstract at ADS
---------------------------------------------------------
Title: Probing stellar interiors with MONS
Authors: Christensen-Dalsgaard, J.
1998mons.proc...17C Altcode:
The MONS satellite, under consideration within the Danish
small-satellite programme, aims at carrying out high-precision
photometric observations of oscillations of a limited number of
relatively bright stars. The primary goal is to study solar-like
oscillation in other stars, of expected very low amplitude,
but observation of other types of oscillating stars will also
be carried out, to attempt to detect very weak modes that may be
present. Frequencies and amplitudes of the modes will be used to study
the internal properties of the stars and the mechanisms responsible
for the oscillations. In this way, a better understanding will be
sought of the structure and evolution of the stars, and of the physical
processes that controls them. Here I summarize the properties of the
relevant stellar oscillations and discuss how these properties may
provide information about the stellar interiors.
---------------------------------------------------------
Title: Stellar background power spectra from hydrodynamical
simulations of stellar atmospheres
Authors: Trampedach, R.; Christensen-Dalsgaard, J.; Nordlund, A.;
Stein, R. F.
1998mons.proc...59T Altcode:
The non-p-mode contribution to the temporal irradiance or velocity
spectra of the Sun has for a long time been considered as noise,
but in recent years it has gradually been appreciated as the signal of
granulation. Accordingly these spectra are now referred to as background
spectra. We hope that further analysis of these background spectra
will serve two purposes: to provide information about convection in
other stars; and, as the background still constitutes a noise source
when looking for p- and in particular g-modes of solar type stars,
to provide us with stricter limits as to what is observable. Based on
hydrodynamical simulations of convection in the atmospheres of the Sun,
alpha Cen A and Procyon, we calculate irradiance and velocity spectra
and infer a few properties of these spectra. Due to the limited
horizontal extent of the simulations (covering 6-8 granules each)
we only get a signal from the granulation, whereas effects of meso-
and supergranulation are missing in our signal. At the high-frequency
end we are limited by the horizontal resolution of the simulations.
---------------------------------------------------------
Title: Helioseismic Studies of Differential Rotation in the Solar
Envelope by the Solar Oscillations Investigation Using the Michelson
Doppler Imager
Authors: Schou, J.; Antia, H. M.; Basu, S.; Bogart, R. S.; Bush,
R. I.; Chitre, S. M.; Christensen-Dalsgaard, J.; Di Mauro, M. P.;
Dziembowski, W. A.; Eff-Darwich, A.; Gough, D. O.; Haber, D. A.;
Hoeksema, J. T.; Howe, R.; Korzennik, S. G.; Kosovichev, A. G.;
Larsen, R. M.; Pijpers, F. P.; Scherrer, P. H.; Sekii, T.; Tarbell,
T. D.; Title, A. M.; Thompson, M. J.; Toomre, J.
1998ApJ...505..390S Altcode:
The splitting of the frequencies of the global resonant acoustic modes
of the Sun by large-scale flows and rotation permits study of the
variation of angular velocity Ω with both radius and latitude within
the turbulent convection zone and the deeper radiative interior. The
nearly uninterrupted Doppler imaging observations, provided by the
Solar Oscillations Investigation (SOI) using the Michelson Doppler
Imager (MDI) on the Solar and Heliospheric Observatory (SOHO) spacecraft
positioned at the L<SUB>1</SUB> Lagrangian point in continuous sunlight,
yield oscillation power spectra with very high signal-to-noise ratios
that allow frequency splittings to be determined with exceptional
accuracy. This paper reports on joint helioseismic analyses of
solar rotation in the convection zone and in the outer part of the
radiative core. Inversions have been obtained for a medium-l mode set
(involving modes of angular degree l extending to about 250) obtained
from the first 144 day interval of SOI-MDI observations in 1996. Drawing
inferences about the solar internal rotation from the splitting data
is a subtle process. By applying more than one inversion technique
to the data, we get some indication of what are the more robust
and less robust features of our inversion solutions. Here we have
used seven different inversion methods. To test the reliability and
sensitivity of these methods, we have performed a set of controlled
experiments utilizing artificial data. This gives us some confidence
in the inferences we can draw from the real solar data. The inversions
of SOI-MDI data have confirmed that the decrease of Ω with latitude
seen at the surface extends with little radial variation through much
of the convection zone, at the base of which is an adjustment layer,
called the tachocline, leading to nearly uniform rotation deeper
in the radiative interior. A prominent rotational shearing layer in
which Ω increases just below the surface is discernible at low to
mid latitudes. Using the new data, we have also been able to study the
solar rotation closer to the poles than has been achieved in previous
investigations. The data have revealed that the angular velocity
is distinctly lower at high latitudes than the values previously
extrapolated from measurements at lower latitudes based on surface
Doppler observations and helioseismology. Furthermore, we have found
some evidence near latitudes of 75° of a submerged polar jet which
is rotating more rapidly than its immediate surroundings. Superposed
on the relatively smooth latitudinal variation in Ω are alternating
zonal bands of slightly faster and slower rotation, each extending
some 10° to 15° in latitude. These relatively weak banded flows
have been followed by inversion to a depth of about 5% of the solar
radius and appear to coincide with the evolving pattern of “torsional
oscillations” reported from earlier surface Doppler studies.
---------------------------------------------------------
Title: Opacity effects on the solar interior. I. Solar structure
Authors: Tripathy, S. C.; Christensen-Dalsgaard, J.
1998A&A...337..579T Altcode: 1997astro.ph..9206T
Despite recent major advances, the opacity remains an important source
of uncertainty in the calculation of solar models, and hence of
solar oscillation frequencies. Hence it is of substantial interest
to investigate the sensitivity of solar structure to changes in
the opacity. Furthermore, we may hope from the precise helioseismic
inferences of solar structure to obtain information about possible
corrections to the opacities used in the model calculation. Here we
carry out detailed calculations of the influence on solar models of
changes in the opacity, including also evolutionary effects. We find
that over the relevant range the response of the model is approximately
linear in the opacity change, allowing the introduction of opacity
kernels relating a general opacity change to the corresponding model
changes. Changes in the convection zone can be characterized entirely
by the change in the initial composition and mixing length required
to calibrate the model.
---------------------------------------------------------
Title: Accurate Determination of the Solar Photospheric Radius
Authors: Brown, T. M.; Christensen-Dalsgaard, J.
1998ApJ...500L.195B Altcode: 1998astro.ph..3131B
The Solar Diameter Monitor measured the duration of solar meridian
transits during the 6 years 1981-1987, spanning the declining half of
solar cycle 21. We have combined these photoelectric measurements with
models of the solar limb-darkening function, deriving a mean value for
the solar near-equatorial radius of 695.508+/-0.026 Mm. Annual averages
of the radius are identical within the measurement error of +/-0.037 Mm.
---------------------------------------------------------
Title: The 'Standard' Sun Modelling and Helioseismology
Authors: Christensen-Dalsgaard, Jørgen
1998SSRv...85...19C Altcode:
The ‘standard’ solar model is based on a number of simplifying
assumptions and depends on knowledge of the physical properties
of matter in the Sun. Given these assumptions, the constraint that
the model have the observed surface luminosity provides an estimate
of the initial solar helium abundance. From helioseismic analyses
further information can be obtained about the present composition,
including a fairly precise measure of the envelope helium abundance
and an estimate of the hydrogen profile in the radiative interior. It
must be emphasized, however, that these inferences may suffer from
systematic error arising from incomplete knowledge about the equation
of state and opacity of the solar interior.
---------------------------------------------------------
Title: Solar Models with Non-Standard Chemical Composition
Authors: Turcotte, S.; Christensen-Dalsgaard, J.
1998SSRv...85..133T Altcode:
The OPAL monochromatic opacity tables are used to evaluate the impact
of a non-standard chemical composition on solar models.
---------------------------------------------------------
Title: The phase function for stellar acoustic oscillations -
IV. Solar-like stars
Authors: Perez Hernandez, F.; Christensen-Dalsgaard, J.
1998MNRAS.295..344P Altcode: 1997astro.ph..6062P; 1997astro.ph..6062H
In recent years there has been some progress towards detecting
solar-like oscillations in stars. The goal of this challenging project
is to analyse frequency spectra similar to that observed for the Sun
in integrated light. In this context it is important to investigate
what can be learned about the structure and evolution of the stars
from such future observations. Here we concentrate on the structure
of the upper layers, as reflected in the phase function. We show
that it is possible to obtain this function from low-degree p modes,
at least for stars on the main sequence. We analyse its dependence
on several uncertainties in the structure of the uppermost layers. We
also investigate a filtered phase function, which has properties that
depend on the layers around the second helium ionization zone.
---------------------------------------------------------
Title: The Sun is not severely deficient in heavy elements
Authors: Christensen-Dalsgaard, J.; Gough, D. O.
1998Obs...118...25C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Sensitivity of the Sound Speed to the Physical Processes
Included in the Standard Solar Model
Authors: Turck-Chièze, S.; Basu, S.; Berthomieu, G.; Bonanno, A.;
Brun, A. S.; Christensen-Dalsgaard, J.; Gabriel, M.; Morel, P.;
Provost, J.; Turcotte, S.; GOLF Team
1998ESASP.418..555T Altcode: 1998soho....6..555T
The accuracy of the present seismic data allows us to check the
solar internal sound speed down to the core. This is a great support
to check the hypothesis of the classical stellar evolution and to
predict the neutrino fluxes. The interpretation of these measurements
supposes an accurate determination of the structure of the standard
solar model as a first step. It is why a continuing effort has been
devoted to the knowledge of the physical quantities included in this
framework. In this poster we present 6 different solar models calculated
by different groups of the GOLF consortium. These models include the
most recent progress in atomic physics and nuclear physics. Then, we
discuss the sensitivity of the sound speed difference, between GOLF+MDI
observations and models, to different ingredients, in peculiar to the
opacity coefficients and the determination of the solar age.
---------------------------------------------------------
Title: Slow Poles and Shearing Flows from Heliospheric Observations
with MDI and GONG Spanning a Year
Authors: Schou, J.; Christensen-Dalsgaard, J.; Howe, R.; Larsen,
R. M.; Thompson, M. J.; Toomre, J.
1998ESASP.418..845S Altcode: 1998soho....6..845S
We invert one year of coeval high-resolution rotational splitting data
(up to degree l 250) from GONG and SOI-MDI. The first 4 months of
MDI data uncovered several new features in the rotation of the solar
convective envelope: surface and subsurface zonal bands corresponding
to the so-called torsional oscillations, superimposed on the overall
smooth latitudinal surface rotation; a drop in the near-polar surface
rotation rate below the rate extrapolated from lower latitudes; and an
indication of a prograde jet-like feature at high latitudes at a depth
of about 5 percent of the solar radius. Using the 1 year of data from
the MDI and GONG instruments, we test the robustness and stationarity of
these features. As an aid to testing the robustness of our inferences,
we use two independent inversion methods (2-D regularized least squares
and SOLA) and apply them to the splitting data obtained from both GONG
and MDI.
---------------------------------------------------------
Title: Problems, Prospects and Promises of Helio- and
Asteroseismology: A Summary of the Workshop
Authors: Christensen-Dalsgaard, J.
1998ESASP.418...17C Altcode: 1998soho....6...17C
No abstract at ADS
---------------------------------------------------------
Title: Theoretical aspects of asteroseismology
Authors: Christensen-Dalsgaard, J.
1998IAUS..185..245C Altcode:
Unlike the solar case, seismic investigations of the distant stars
must be based on data for modes of relatively low degree. On the other
hand, stars display a much broader range of modes than so far observed
in the Sun, including g modes in several types of stars. Furthermore,
the ability to probe the conditions in a broad range of stars, covering
different stellar masses and evolutionary stages, is crucial for tests
of stellar evolution theory and information about the properties of
stellar interiors. I discuss the properties of the observed or expected
oscillations in stars, with special emphasis on the diagnostic potential
of the frequencies. In some cases inversion for aspects of the stellar
internal rotation and structure might be possible, for example by
analyzing a combination of g modes and low-order p modes. However,
this requires identification of the modes in the complex spectra of
oscillations, which still presents severe problems.
---------------------------------------------------------
Title: Rotation of the Solar Core Inferred from GONG Data
Authors: Rabello-Soares, M. C.; Appourchaux, T.; Christensen-Dalsgaard,
J.
1998ESASP.418..837R Altcode: 1998soho....6..837R
We present inferences of the solar core rotation derived from GONG
frequency splittings. The GONG data for the low-degree modes (l <=
6) are for the one year period Aug. 1995-1996; these splittings
were determined using a new method of fitting heliosismic spectra
(Rabello-Soares & Appourchaux 1998). These are combined with
GONG data for higher degree modes, as obtained by the GONG team (Hill
et al. 1996). We have employed a new two-dimensional implementation
of the optimally localized averages (OLA) inversion method (Chaplin
et al. 1998). As in one dimension, the OLA produces better-localized
averaging kernels than do least-squares techniques. This is particularly
beneficial in the deep interior, where it is in any case difficult to
obtain localized information.
---------------------------------------------------------
Title: The Stellar and Planetary Explorer (SPEX) Mission
Authors: Schou, J.; Scherrer, P. H.; Brown, T. M.; Frandsen, S.;
Horner, S. D.; Korzennik, S. G.; Noyes, R. W.; Tarbell, T. D.; Title,
A. M.; Walker, A. B. C., II; Weiss, W. W.; Bogart, R. S.; Bush, R. I.;
Christensen-Dalsgaard, J.; Hoeksema, J. T.; Jones, A.; Kjeldsen, H.
1998ESASP.418..401S Altcode: 1998soho....6..401S
The Stellar and Planetary Explorer (SPEX) is a mission designed
to search for terrestrial sized planets around sun-like stars using
precise photometry. The planets will be detected by searching for the
decrease in brightness associated with transits of the planets in front
of their parent stars. One of the secondary scientific objective of
SPEX is to do asteroseismology on a number of sun-like stars. SPEX
is designed as a secondary payload on a commercial communications
satellite and will have a design life time of three years. We will
provide an overview of the SPEX scientific objectives and design,
with particular emphasis on the prospects for doing asteroseismology.
---------------------------------------------------------
Title: Seismic Constraints on Sound Speed in the Solar Core
Authors: Rabello-Soares, M. C.; Christensen-Dalsgaard, J.; Thompson,
M. J.
1998ESASP.418..511R Altcode: 1998soho....6..511R
Direct seismic information about the structure of the solar core from
measured p-mode frequencies is based on only a modest number of modes
of low degree. Hence it is difficult to obtain local measures of,
for example, the variation of the sound speed in the core. However,
even averages of the central sound-speed difference between the Sun
and a model would be of considerable diagnostic value, provided that
these averages could be effectively restricted to a sufficiently
small region. Chaplin et al. (1998) developed a technique, based on
the method of optimally localized averages introduced by Backus &
Gilbert, to construct an average of the rotation of the solar core,
and this was applied with some success to combined BiSON and LOWL
data. Here we investigate a similar procedure for constructing averages
of the sound-speed difference between the Sun and a reference model,
localized to the core. These provide seismic constraints on core
structure that are only minimally sensitive to uncertainties in other
regions of the Sun.
---------------------------------------------------------
Title: Testing the helioseismic determination of opacity corrections
Authors: Tripathy, S. C.; Christensen-Dalsgaard, J.
1998BASI...26..163T Altcode: 1997astro.ph..3170T
We investigate the effect of localized opacity modifications on the
sound-speed profile of solar models. The sound-speed difference between
the Sun and a solar model is used to deduce the opacity correction that
would be required to bring the model into agreement with the Sun. We
test this procedure on artificial data for a pair of solar models and
apply it to the solar sound speed as inferred from inversion of LOWL
observed frequencies. We show that a solar model constructed with the
appropriately modified opacity has a sound-speed profile very similar
to that of the Sun.
---------------------------------------------------------
Title: The Base of the Convection Zone and the Solar Magnetic Cycle:
Seismic Detection of Their Connection
Authors: Monteiro, Mario J. P. F. G.; Christensen-Dalsgaard, Jorgen;
Thompson, Michael J.
1998ESASP.418..495M Altcode: 1998soho....6..495M
It is now possible to detect small variations with time of the
characteristics of the transition at the bottom of the solar convection
zone, as determined from the periodic signal in the frequencies
(Christensen-Dalsgaard et.al. 1995, Basu 1997). Such measurements may
allow us to establish whether and in what manner the deeper convection
zone changes with the solar magnetic cycle. This would be important
for understanding the dynamics at the base of the convection zone and
the origin of the solar cycle. It will also help in understanding
the physics of convective overshoot, its interaction with rotation
and magnetic fields, and the effects on the stratification. In this
work we investigate the limits on the detectability of small changes
in the stratification at the base of the convection zone, and attempt
to constrain the amplitude of the changes from currently available
seismic data.
---------------------------------------------------------
Title: Asteroseismology
Authors: Christensen-Dalsgaard, Jørgen
1998Ap&SS.261....1C Altcode: 1999Ap&SS.261....1C
No abstract at ADS
---------------------------------------------------------
Title: Implications of Heavy-Element Settling for the Seismology of
the αCen System
Authors: Turcotte, S.; Christensen-Dalsgaard, J.
1998ESASP.418..407T Altcode: 1998soho....6..407T
Oscillation frequencies for calibrated models of α Cen A and B are
presented. The models incorporate a consistent treatment of diffusion
of He and heavy elements (Turcotte et. al 1998). Previous models have
neglected the impact of settling of heavy elements on the evolution
of the α Cen stars. Of particular interest is its implications for
the evolution of the convective core of α Cen A. Some models are
considered in which the extent of the convective overshoot at the core
and beneath the surface convective zones are varied to estimate their
influence on the models. The oscillation frequencies for α Cen A are
examined in particular to verify to what extent they can be of use to
help constrain the convective core overshoot.
---------------------------------------------------------
Title: MCD Inversion for Sound Speed using Time-Distance Data
Authors: Jensen, J. M.; Jacobsen, B. H.; Christensen--Dalsgaard, J.
1998ESASP.418..635J Altcode: 1998soho....6..635J
We present an inversion technique based on a MultiChannel Deconvolution
(MCD) algorithm that speeds up the calculations by doing the
computational work in the Fourier domain. As a result, inversions
can be done in a matter of seconds, even for high-volume data
sets such as those from the SOHO satellite. This technique has been
developed recently within geophysics for inversion of electromagnetic
data. It is based on the Born approximation where one inverts for
perturbations around a reference model. Because the reference model has
horizontal translational invariance, the forward calculation becomes a
convolution of the model with the Frechet kernels, which according to
the convolution theorem can be performed as a simple multiplication in
the Fourier domain. Also, inverse calculations speed up significantly
in the Fourier domain. A reliable inversion requires correct Frechet
kernels. These are currently unknown. The Frechet kernels which we
have used so far are based on the Gaussian beam concept, which is
a step beyond a pure ray approximation. The Fourier transformation
implies periodicity. This introduces errors in the inversion near the
edges of the area investigated. These errors are of the same order of
magnitude as errors introduced by zero padding the data. We will show
the details of the MCD technique, examples of resolution kernels and
results of inversions performed on helioseismic data.
---------------------------------------------------------
Title: The influence of magnetic fields on radiative damping of
magnetoatmospheric oscillations
Authors: Banerjee, Dipankar; Hasan, S. S.; Christensen-Dalsgaard, J.
1998IAUS..185..423B Altcode:
We examine the non adiabatic effects on the modes of an isothermal
stratified magnetic atmosphere. The present investigation
is a continuation of earlier work by Banerjee, Hasan &
Christensen-Dalsgaard (1995, 1996, 1997), where the interaction of
various elementary modes in a stratified magnetised atmosphere
was studied in the purely adiabatic limit. The inclusion of
radiative dissipation in magnetoatmospheric wave problem - even in
the over simplified Newtonian Cooling approximation - is of great
importance. Including Newtonian Cooling, in the weak field limit, an
analytic expression for the dispersion relation is derived which allows
the effect of weak magnetic field on the modes to be studied. We examine
the nature of the eigen frequency curves in the diagnostic diagram and
find that, similar to the previous analysis, the modes undergo avoided
crossings. We study the full frequency spectrum and the interaction
amongst various modes. Strong mode coupling in the avoided crossing
regions permits energy leakage. Our results, find application in the
analysis of waves in flux-tubes on the Sun. We study the influence of
magnetoatmospheric waves on spectral line profiles.
---------------------------------------------------------
Title: The 'Standard' Sun
Authors: Christensen-Dalsgaard, J.
1998sce..conf...19C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Helioseismology and Solar Neutrinos
Authors: Christensen-Dalsgaard, J.
1998tsra.conf..694C Altcode: 1997astro.ph..2094C
Helioseismology has provided very precise information about the
solar internal sound speed and density throughout most of the solar
interior. The results are generally quite close to the properties
of standard solar models. Since the solar oscillation frequencies
do not provide direct information about temperature and composition,
the helioseismic results to not completely rule out an astrophysical
solution to the discrepancy between the predicted and measured
neutrino fluxes from the Sun. However, such a solution does appear
rather implausible.
---------------------------------------------------------
Title: Improved SOLA Inversions of MDI Data
Authors: Larsen, R. M.; Christensen-Dalsgaard, J.; Kosovichev, A. G.;
Schou, J.
1998ESASP.418..813L Altcode: 1998soho....6..813L
We present a new version of 2d-SOLA, where the target functions have
been modified to match the behavior of the mode kernels near the
rotation axis and to minimize near-surface contributions. Inversion
of artificial data show that these modifications significantly improve
the effective resolution near the pole, which allows us to assess the
reliability of the high-latitude features seen by other inversion
methods. Most importantly, our new inversions seem to confirm the
detection of a submerged polar jet previously seen in the 2d-RLS
inversions reported by Schou et al. 1998. A test of the robustness of
the improved method is carried out by inverting artificial data from
the MDI Hare and Hounds exercise. We analyze the averaging kernels and
error propagation of the method, and also describe the error-correlation
between different points in the solution, the latter being a potential
source of spurious features in the solutions as pointed out by Howe
and Thompson, 1996. So far, helioseismic datasets given in the form of
a-coefficients have been inverted under the assumption that the errors
in different a-coefficients are uncorrelated. The MDI peak-bagging
procedure, however, does produce estimates of the error-correlation
between a-coefficients within the same multiplet. Here we investigate
the effect of including this knowledge in the inversions.
---------------------------------------------------------
Title: Tests of Convective Frequency Effects with SOI/MDI High-Degree
Data
Authors: Rosenthal, C. S.; Christensen-Dalsgaard, J.; Kosovichev,
A. G.; Nordlund, A. A.; Reiter, J.; Rhodes, E. J., Jr.; Schou, J.;
Stein, R. F.; Trampedach, R.
1998ESASP.418..521R Altcode: 1998astro.ph..7066R; 1998soho....6..521R
Advances in hydrodynamical simulations have provided new insight into
the effects of convection on the frequencies of solar oscillations. As
more accurate observations become available, this may lead to an
improved understanding of the dynamics of convection and the interaction
between convection and pulsation (Rosenthal et al. 1999). Recent
high-resolution observations from the SOI/MDI instrument on the
SOHO spacecraft have provided the so-far most-detailed observations
of high-degree modes of solar oscillations, which are particularly
sensitive to the near-surface properties of the Sun. Here we present
preliminary results of a comparison between these observations and
frequencies computed for models based on realistic simulations of
near-surface convection. Such comparisons may be expected to help
in identifying the causes for the remaining differences between the
observed frequencies and those of solar models.
---------------------------------------------------------
Title: Asteroseismology and Stellar Rotation
Authors: Kjeldsen, H.; Arentoft, T.; Bedding, T.;
Christensen-Dalsgaard, J.; Frandsen, S.; Thompson, M. J.
1998ESASP.418..385K Altcode: 1998soho....6..385K
Δ Scuti stars are observed to rotate with surface velocities of the
order 100-200 km/s corresponding to a rotation period of about one
day. Rotation removes the frequency degeneracy in the azimuthal order m
of the modes and thus allows the possibility of determining the angular
velocity inside the star. Rotation also perturbs the internal structure
of the star, making the star oblate, as well as changing the internal
stratification. Such perturbations will result in a systematic change of
all frequencies, if compared with a non-rotating star of similar mass
and age. In this way even the radial (l = 0) mode frequencies will be
affected by the rotation of the star. We discuss how basic properties
as well as frequencies of δ Scuti stars are affected by fast rotation
and we investigate the impact of these changes on our interpretation
of observed frequencies used in an asteroseismic analysis. We discuss
the results in the light of the currently available frequency data
for δ Scuti stars in the Praesepe cluster.
---------------------------------------------------------
Title: HIPPARCOS Parallaxes for eta Boo and kappa^1 Boo: Two Successes
for Asteroseismology
Authors: Bedding, Timothy R.; Kjeldsen, Hans; Christensen-Dalsgaard,
Jorgen
1998ASPC..154..741B Altcode: 1998csss...10..741B; 1997astro.ph..9005B
The release of the Hipparcos catalogue provides an opportunity to
check results from asteroseismology. We discuss two stars: (i) Eta
Boo (G subgiant), in which we have previously reported detection of
solar-like oscillations; and (ii) Kappa2Boo, a multi-mode Delta Scuti
variable. The Hipparcos parallaxes for both stars are in excellent
agreement with oscillation results.
---------------------------------------------------------
Title: A Study of the Parameters for Solar Structure Inversion Methods
Authors: Rabello-Soares, M. C.; Basu, Sarbani; Christensen-Dalsgaard,
J.
1998ESASP.418..505R Altcode: 1998soho....6..505R
The observed solar p-mode frequencies provide an extremely useful
diagnostic of the internal structure of the Sun, and permit us to
test in considerable detail the physics used in the theory of stellar
structure. Two implementations of the optimally localized averages
(OLA) method are amongst the most commonly used techniques for inverting
helioseismic data, namely the Subtractive Optimally Localized Averages
(SOLA) and Multiplicative Optimally Localized Averages (MOLA). In both
of them, there are a number of parameters that must be chosen in order
to find the solution. Proper choice of the parameters is very important
to determine correctly the variation of the internal structure along
the solar radius. In this work, we make a detailed analysis on the
influence of each parameter on the solution and indicate how to arrive
at an optimal set of parameters for a given data set.
---------------------------------------------------------
Title: Turbulence in Astrophysics: Stars
Authors: Canuto, V. M.; Christensen-Dalsgaard, J.
1998AnRFM..30..167C Altcode:
Turbulence is ubiquitous in astrophysics, ranging from cosmology,
interstellar medium to stars, supernovae, accretion disks,
etc. Large scales and small viscosities combine to form large
Reynolds numbers. Because it is not possible in a single article
to review all the above scenarios, we limit ourselves to stars,
in which thermal instabilities give rise to turbulent convection as
the dominant heat transport mechanism. (Accretion disks, where shear
instabilities dominate the outward transport of angular momentum, will
be the subject of a second article, planned for Volume 31.) Because
of the lack of a satisfactory theory, turbulence constitutes a
bottleneck that prevents astrophysical models from being fully
predictive. Because continued use of phenomenological turbulence
expressions would make astrophysical models perennially unpredictive,
a way must be found to make astrophysical models as prognostic as
possible. In addition to the difficulties brought about by turbulence,
astrophysical settings introduce "malicious conditions," of which the
most refractory to a satisfactory quantification are compressibility
(caused by the large density excursions that characterize convective
zones in stars) and rotation. Basic understanding of how they affect
turbulence in general is still rather sketchy. Reasons for the choice
of stars and accretion disks as prototype examples are the following:
The underlying instabilities are very basic; laboratory and direct
numerical simulations data help constrain theoretical models; and new
observational data, especially from helioseismology, help discriminate
among different models with unprecedented accuracy.
---------------------------------------------------------
Title: Effects of Line Asymmetries on the Determination of Solar
Oscillation Frequencies
Authors: Christensen-Dalsgaard, J.; Rabello-Soares, M. C.; Rosenthal,
C. S.; Thompson, M. J.
1998ESASP.418..147C Altcode: 1998soho....6..147C
Despite the strong evidence that the peaks in the spectrum of solar
oscillations are asymmetric, most determinations of mode frequencies
have been based on fits of symmetric Lorentzian profiles to the Fourier
or power spectra of oscillation time strings. The systematic errors
resulting from neglecting the line asymmetry could have serious effects
on inversions for the solar internal structure and rotation. Here we
analyze artificial data based on simple models of the intrinsic line
asymmetry. By fitting Lorentzians to the resulting spectra, we estimate
the likely properties of the errors introduced in the frequencies and
consider the possible effects on the inversions.
---------------------------------------------------------
Title: Seismic detection of boundaries of stellar convective regions
Authors: Monteiro, M. J. P. F. G.; Christensen-Dalsgaard, J.; Thompson,
M. J.
1998IAUS..185..315M Altcode:
The seismic study of the base of the convection zone in the Sun (eg
Christensen-Dalsgaard et al 1995, MNRAS 276, 283) has been successful
in determining not only the position of the base of the convective
envelope, but also the characteristics of this transition layer. In
this poster we consider other types of star possessing convective
envelopes or cores and seek to establish the conditions under which we
may determine important characteristics of their convective regions. In
particular we may hope to establish seismologically that a star does
indeed posess a convective envelope or core and to measure the size
of that convective region. The method used consists in identifying a
signal in the observed frequencies whose characteristics depend on
the location of the border of a convective region in the star. The
limitations in terms of observational uncertainties and stellar
characteristics are presented.
---------------------------------------------------------
Title: New eyes to see inside the sun and stars : pushing the limits
of helio- and asteroseismology with new observations from the ground
and from space
Authors: Deubner, Franz-Ludwig; Christensen-Dalsgaard, Joergen;
Kurtz, Don
1998IAUS..185.....D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Detection of the Lower Boundary of Stellar Convective Envelopes
from Seismic Data
Authors: Monteiro, Mário J. P. F. G.; Christensen-Dalsgaard, Jørgen;
Thompson, Michael J.
1998Ap&SS.261...41M Altcode: 1999Ap&SS.261...41M
No abstract at ADS
---------------------------------------------------------
Title: Solar Models with Non-Standard Chemical Composition
Authors: Turcotte, S.; Christensen-Dalsgaard, J.
1998sce..conf..133T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Diagnostic Potential of the Solar f Modes
Authors: Chitre, S. M.; Christensen-Dalsgaard, J.; Thompson, M. J.
1998ESASP.418..141C Altcode: 1998soho....6..141C
The frequencies of f modes of intermediate and high degree l of a
stellar model in hydrostatic equilibrium are essentially given by ω
= square root {g k<SUB>h</SUB>}, where to a good first approximation
g is the surface gravitational acceleration G M / R<SUP>2</SUP> and
k<SUB>h</SUB> = square root {l(l+1)}/R, M and R being the mass and
radius respectively of the model. More precisely, the frequency is
determined not simply by the surface values of these quantities but
by a weighted average over the region where the mode has appreciable
amplitude. Thus the frequencies of the f modes depend on the density
stratification in the near-surface region (Gough 1985, 1993). Given
the very high accuracy to which the f-mode frequencies can now
be determined, in particular from the SOI/MDI experiment on SOHO,
this sensitivity may provide an important diagnostic of the Sun's
near-surface structure. We investigate this sensitivity, in terms of
numerical kernels and the simple analytical approximation derived by
Gough. In addition, we consider the possibilities for investigating
time variations and asphericity in solar structure on the basis of
f-mode observations.
---------------------------------------------------------
Title: The Problem of Mode Identification in roAp Stars: Multi-Colour
Photometry
Authors: Medupe, R.; Kurtz, D. W.; Christensen-Dalsgaard, J.
1998ASPC..135..197M Altcode: 1998hcsp.conf..197M
Dziembowski (1977) proposed a modified Baade-Wesselink method for
mode identification in a non-radially pulsating star with a well
determined radius. Balona & Stobie (1979) recast this technique in
an observationally feasible form, and applied it to some stars. This
technique works for b Cephei, 53 Persei, d Scuti, Cepheid and ZZ
Ceti variables, but does not work for rapidly oscillating Ap (roAp)
stars. Here we outline the problem of mode identification in roAp stars
and show how we shall attempt to solve it. We also apply the linearised
expression (as in Watson 1988), for non-radial light variation, combined
with the latest model atmospheres of roAp stars to the light and colour
variation data to show the effect of improved model atmospheres on
the Baade-Wesselink method and other mode discrimination techniques.
---------------------------------------------------------
Title: The SOI-MDI High-Latitude Jet: the Evidence For and Against
Authors: Howe, R.; Antia, H.; Basu, S.; Christensen-Dalsgaard, J.;
Korzennik, S. G.; Schou, J.; Thompson, M. J.
1998ESASP.418..803H Altcode: 1998soho....6..803H
The apparent detection of a prograde jet at latitude 75-circ and at a
radius of about 0.95R<SUB>odot</SUB> in some inversions of rotation data
from SOI--MDI (Schou et al., 1998) has excited considerable interest,
but whether the jet really exists in the solar interior is certainly not
yet firmly established. The detection of the feature is sensitive both
to the inversion techniques used and to the methods of mode parameter
estimation used to generate the input data. In particular, the feature
is much more apparent in Regularized Least-Squares inversions than
in inversions using an Optimally Localized Average approach, and is
not detected at all in the present GONG data when analysed with the
GONG peakfinding algorithm, or indeed in SOI data when analysed with
the GONG algorithm. Therefore in this poster we examine critically
the current evidence for the source and existence of this jet in the
light of forward and inverse analyses.
---------------------------------------------------------
Title: The Effect of Differential Settling and of Revised Abundances
on Solar Oscillation Frequencies
Authors: Turcotte, S.; Christensen--Dalsgaard, J.
1998ESASP.418..561T Altcode: 1998soho....6..561T
The effect of including consistent diffusion of heavy elements on the
predicted solar oscillation frequencies is investigated. The models are
calculated using the OPAL monochromatic opacities and include the effect
of differential settling of all the elements included in their database
(Turcotte et. al, 1998). The impact of the newly proposed reduction
of photospheric CNO abundances by 10% (Grevesse & Sauval, 1998)
on the structure and oscillation frequencies is also investigated.
---------------------------------------------------------
Title: Near-surface constraints on the structure of stellar convection
zones
Authors: Trampedach, R.; Christensen-Dalsgaard, J.; Nordlund, A.;
Stein, R.
1997ASSL..225...73T Altcode: 1997scor.proc...73T
By simulating the convection in the upper layers of six different stars
and matching these simulations to 1D-mixing length models using the
same input physics, we have been able to infer the behaviour of the
mixing-length parameter, $\alpha$, as the stellar parameters changes.
---------------------------------------------------------
Title: Solar internal sound speed as inferred from combined BiSON
and LOWL oscillation frequencies
Authors: Basu, Sarbani; Christensen-Dalsgaard, J.; Chaplin, W. J.;
Elsworth, Y.; Isaak, G. R.; New, R.; Schou, J.; Thompson, M. J.;
Tomczyk, S.
1997MNRAS.292..243B Altcode: 1997astro.ph..2105B
Observations of the Sun with the LOWL instrument provide a homogeneous
set of solar p-mode frequencies from low to intermediate degree that
allow one to determine the structure of much of the solar interior
avoiding systematic errors that are introduced when different data sets
are combined, i.e., principally the effects of solar cycle changes on
the frequencies. Unfortunately, the LOWL data set contains very few of
the lowest-degree modes, which are essential for determining reliably
the structure of the solar core - in addition, these lowest-degree data
have fairly large associated uncertainties. However, observations made
by the Birmingham Solar-Oscillations Network (BiSON) in integrated
sunlight provide high-accuracy measurements of a large number of
low-degree modes. In this paper we demonstrate that the low-degree mode
set of the LOWL data can be successfully combined with the more accurate
BiSON data, provided the observations are contemporaneous for those
frequencies where the solar cycle induced effects are important. We
show that this leads to a factor of 2 decrease in the error on the
inferred sound speed in the solar core. We find that the solar sound
speed is higher than in solar models for r<0.2Rsolar. The density
of the solar core is, however, lower than that in solar models.
---------------------------------------------------------
Title: Rotation and Zonal Flows in the Solar Envelope from the
SOHO/MDI Observations
Authors: Scherrer, P. H.; Schou, J.; Bogart, R. S.; Bush, R. I.;
Hoeksema, J. T.; Kosovichev, A. G.; Antia, H. M.; Chitre, S. M.;
Christensen-Dalsgaard, J.; Larsen, R. M.; Pijpers, F. P.; Eff-Darwich,
A.; Korzennik, S. G.; Gough, D. O.; Sekii, T.; Howe, R.; Tarbell,
T.; Title, A. M.; Thompson, M. J.; Toomre, J.
1997AAS...191.7310S Altcode: 1997BAAS...29.1322S
We report on the latest inferences concerning solar differential
rotation that have been drawn from the helioseismic data that are now
available from the Solar Oscillations Investigation (SOI) using the
Michelson Doppler Imager (MDI) on the Solar and Heliospheric Observatory
(SOHO). That spacecraft is positioned in a halo orbit near the Sun-Earth
Lagrangian point L_1, in order to obtain continuous Doppler-imaged
observations of the sun with high spatial fidelity. Doppler velocity,
intensity and magnetic field images are recorded, based on modulations
of the 676.8 nm Ni I solar absorption line. The high spatial resolution
of MDI thereby permits the study of many millions of global resonant
modes of solar oscillation. Determination and subsequent inversion
of the frequencies of these modes, including the degeneracy-splitting
by the rotation of the sun, enables us to infer how the sun's angular
velocity varies throughout much of the interior. The current MDI data
are providing substantial refinements to the helioseismic deductions
that can be made about differential rotation both within the convection
zone and in its transition to the radiative interior. The shearing
layer evident in the angular velocity Omega just below the solar
surface is becoming better defined, as is the adjustment layer or
tachocline near the base of the convection zone. The MDI data are also
revealing a prominent decrease in Omega at high latitudes from the
rotation rate expressed by a simple three-term expansion in latitude
that was originally deduced from surface Doppler measurements. Further,
there are indications that a submerged polar vortex involving somewhat
faster Omega than its surroundings exists at about 75(deg) in latitudes.
---------------------------------------------------------
Title: The influence of radiative damping on the modes of a magnetized
isothermal atmosphere
Authors: Banerjee, D.; Hasan, S. S.; Christensen-Dalsgaard, J.
1997ASSL..225..277B Altcode: 1997scor.proc..277B
We examine the influence of radiative damping on the modes of an
isothermal magnetized plasma. This investigation is an extension of
earlier work by Hasan \& Christensen-Dalsgaard (1992) and Banerjee,
Hasan \& Christensen-Dalsgaard (1995, 1996), which treated the
effects of a uniform vertical magnetic field on the adiabatic modes
of a stratified atmosphere. We focus on the properties of the Lamb
mode and examine its interaction with a magnetic mode. We show that
radiative dissipation can significantly alter the Lamb-mode frequency
and lead to a enhanced damping of the waves at the avoided crossings
in the $k-\omega$ diagram. This mechanism could be important for wave
damping in flux tubes on the Sun.
---------------------------------------------------------
Title: Effects of convection on the mean solar structure
Authors: Christensen-Dalsgaard, J.
1997ASSL..225....3C Altcode: 1997astro.ph..2104C; 1997scor.proc....3C
The overall framework for the study of solar convection and oscillations
is the spherically symmetric component of solar structure. I discuss
those properties of the solar interior which depend on convection and
other possible hydrodynamical motion and the increasingly detailed
information about the structure which is provided by helioseismic
data. The most basic dependence of solar models on convection is the
calibration to fix the solar radius. The dominant causes for differences
in oscillation frequencies between the Sun and solar models seem to
be located near the top of the convection zone. However, there is
also evidence for possible weak mixing below the convection zone and
perhaps in the solar core. The former, at least, might be induced by
penetration of convective motion into the stable layers below.
---------------------------------------------------------
Title: SCORe'96 : Solar Convection and Oscillations and their
Relationship
Authors: Pijpers, F. P.; Christensen-Dalsgaard, J.; Rosenthal, C. S.
1997ASSL..225.....P Altcode: 1997scor.proc.....P
No abstract at ADS
---------------------------------------------------------
Title: First View of the Solar Core from GOLF Acoustic Modes
Authors: Turck-Chièze, S.; Basu, S.; Brun, A. S.;
Christensen-Dalsgaard, J.; Eff-Darwich, A.; Lopes, I.; Pérez
Hernández, F.; Berthomieu, G.; Provost, J.; Ulrich, R. K.; Baudin,
F.; Boumier, P.; Charra, J.; Gabriel, A. H.; Garcia, R. A.; Grec,
G.; Renaud, C.; Robillot, J. M.; Roca Cortés, T.
1997SoPh..175..247T Altcode:
After 8 months of nearly continuous measurements the GOLF instrument,
aboard SOHO, has detected acoustic mode frequencies of more than 100
modes, extending from 1.4 mHz to 4.9 mHz. In this paper, we compare
these results with the best available predictions coming from solar
models. To verify the quality of the data, we examine the asymptotic
seismic parameters; this confirms the improvements achieved in solar
models during the last decade.
---------------------------------------------------------
Title: Performance and Early Results from the GOLF Instrument Flown
on the SOHO Mission
Authors: Gabriel, A. H.; Charra, J.; Grec, G.; Robillot, J. -M.;
Roca Cortés, T.; Turck-Chièze, S.; Ulrich, R.; Basu, S.; Baudin,
F.; Bertello, L.; Boumier, P.; Charra, M.; Christensen-Dalsgaard, J.;
Decaudin, M.; Dzitko, H.; Foglizzo, T.; Fossat, E.; García, R. A.;
Herreros, J. M.; Lazrek, M.; Pallé, P. L.; Pétrou, N.; Renaud, C.;
Régulo, C.
1997SoPh..175..207G Altcode:
GOLF in-flight commissioning and calibration was carried out during the
first four months, most of which represented the cruise phase of SOHO
towards its final L1 orbit. The initial performance of GOLF is shown
to be within the design specification, for the entire instrument as
well as for the separate sub-systems. Malfunctioning of the polarising
mechanisms after 3 to 4 months operation has led to the adoption of an
unplanned operating sequence in which these mechanisms are no longer
used. This mode, which measures only the blue wing of the solar sodium
lines, detracts little from the detection and frequency measurements of
global oscillations, but does make more difficult the absolute velocity
calibration, which is currently of the order of 20%. Data continuity
in the new mode is extremely high and the instrument is producing
exceptionally noise-free p-mode spectra. The data set is particularly
well suited to the study of effects due to the excitation mechanism
of the modes, leading to temporal variations in their amplitudes. The
g modes have not yet been detected in this limited data set. In the
present mode of operation, there are no indications of any degradation
which would limit the use of GOLF for up to 6 years or more.
---------------------------------------------------------
Title: Equation of state and helioseismic inversions.
Authors: Basu, S.; Christensen-Dalsgaard, J.
1997A&A...322L...5B Altcode: 1997astro.ph..2162B
Inversions to determine the squared isothermal sound speed and
density within the Sun often use the helium abundance Y as the second
parameter. This requires the explicit use of the equation of state
(EOS), thus potentially leading to systematic errors in the results
if the equations of state of the reference model and the Sun are not
the same. We demonstrate how this potential error can be suppressed. We
also show that it is possible to invert for the intrinsic difference in
the adiabatic exponent {GAMMA}_1_ between two equations of state. When
applied to solar data such inversion rules out the EFF equation of state
completely, while with existing data it is difficult to distinguish
between other equations of state.
---------------------------------------------------------
Title: Effect of Newtonian Cooling on Waves in a Magnetized Isothermal
Atmosphere
Authors: Banerjee, Dipankar; Hasan, S. S.; Christensen-Dalsgaard, J.
1997SoPh..172...53B Altcode: 1997ESPM....8...53B
We examine the influence of nonadiabatic effects on the modes of an
isothermal stratified magnetic atmosphere. The present investigation is
a continuation of earlier work by Hasan and Christensen-Dalsgaard (1992)
and Banerjee, Hasan, and Christensen-Dalsgaard (1995, 1996), where
the interaction of various elementary modes in a stratified magnetized
atmosphere was studied in the purely adiabatic limit. The inclusion of
radiative dissipation based on Newton's law of cooling demonstrates
the importance of this effect in the study of magnetoatmospheric
waves. We analyze the physical nature of magnetoacoustic gravity (or
MAG) oscillations in the presence of Newtonian cooling and find that
the eigenfrequency curves in the diagnostic diagram, as in the previous
analysis, undergo avoided crossings. However, the qualitative nature of
the mode interaction is strongly influenced by radiative dissipation,
which leads to strong mode damping in the avoided-crossing regions. We
demonstrate this effect for the interaction between the Lamb mode and
a magnetic mode. Our results could be important in the analysis of
waves in flux tubes on the Sun.
---------------------------------------------------------
Title: SVD preprocessing of helioseismic data for solar structure
inversion.
Authors: Basu, S.; Christensen-Dalsgaard, J.; Thompson, M. J.
1997A&A...321..634B Altcode:
Helioseismic inversion to determine solar structure is based on the
analysis of very substantial numbers of modes and hence may involve
considerable computational expense. This is particularly true for
inversions using methods of optimally localised averages, which
require inversion of matrices whose order is the number of modes in
the set; yet such methods are desirable to make the full use of the
data. On the other hand, there is considerable redundancy in the
data, different modes carrying almost the same information about
solar structure. Thus, in the unavoidable presence of data errors,
the number of independent pieces of information is generally much
less than the number of modes. This suggests that the mode-set can
be reduced by forming suitable combinations of the data before the
more computationally intensive inversion is performed. We show that
such combinations may be based on singular value decomposition (SVD)
of the problem, leading to a drastically reduced inverse problem whose
solution is essentially indistinguishable from the solution of the
original problem. In addition, the results of the SVD provide insight
into the information content of the helioseismic data.
---------------------------------------------------------
Title: Structure and Rotation of the Solar Interior: Initial Results
from the MDI Medium-L Program
Authors: Kosovichev, A. G.; Schou, J.; Scherrer, P. H.; Bogart, R. S.;
Bush, R. I.; Hoeksema, J. T.; Aloise, J.; Bacon, L.; Burnette, A.; de
Forest, C.; Giles, P. M.; Leibrand, K.; Nigam, R.; Rubin, M.; Scott,
K.; Williams, S. D.; Basu, Sarbani; Christensen-Dalsgaard, J.; Dappen,
W.; Rhodes, E. J., Jr.; Duvall, T. L., Jr.; Howe, R.; Thompson, M. J.;
Gough, D. O.; Sekii, T.; Toomre, J.; Tarbell, T. D.; Title, A. M.;
Mathur, D.; Morrison, M.; Saba, J. L. R.; Wolfson, C. J.; Zayer, I.;
Milford, P. N.
1997SoPh..170...43K Altcode:
The medium-l program of the Michelson Doppler Imager instrument on board
SOHO provides continuous observations of oscillation modes of angular
degree, l, from 0 to ∽ 300. The data for the program are partly
processed on board because only about 3% of MDI observations can be
transmitted continuously to the ground. The on-board data processing,
the main component of which is Gaussian-weighted binning, has been
optimized to reduce the negative influence of spatial aliasing of the
high-degree oscillation modes. The data processing is completed in a
data analysis pipeline at the SOI Stanford Support Center to determine
the mean multiplet frequencies and splitting coefficients. The initial
results show that the noise in the medium-l oscillation power spectrum
is substantially lower than in ground-based measurements. This enables
us to detect lower amplitude modes and, thus, to extend the range of
measured mode frequencies. This is important for inferring the Sun's
internal structure and rotation. The MDI observations also reveal the
asymmetry of oscillation spectral lines. The line asymmetries agree
with the theory of mode excitation by acoustic sources localized in the
upper convective boundary layer. The sound-speed profile inferred from
the mean frequencies gives evidence for a sharp variation at the edge
of the energy-generating core. The results also confirm the previous
finding by the GONG (Gough et al., 1996) that, in a thin layer just
beneath the convection zone, helium appears to be less abundant than
predicted by theory. Inverting the multiplet frequency splittings from
MDI, we detect significant rotational shear in this thin layer. This
layer is likely to be the place where the solar dynamo operates. In
order to understand how the Sun works, it is extremely important to
observe the evolution of this transition layer throughout the 11-year
activity cycle.
---------------------------------------------------------
Title: Are Standard Solar Models Reliable?
Authors: Bahcall, John N.; Pinsonneault, M. H.; Basu, Sarbani;
Christensen-Dalsgaard, J.
1997PhRvL..78..171B Altcode: 1996astro.ph.10250B
The sound speeds of solar models that include element diffusion
agree with helioseismological measurements to a rms discrepancy
of better than 0.2% throughout almost the entire Sun. Models that
do not include diffusion, or in which the interior of the Sun is
assumed to be significantly mixed, are effectively ruled out by
helioseismology. Standard solar models predict the measured properties
of the Sun more accurately than is required for applications involving
solar neutrinos.
---------------------------------------------------------
Title: Internal structure and rotation of the Sun: First results
from MDI data
Authors: Kosovichev, A. G.; Schou, J.; Scherrer, P. H.; Bogart, R. S.;
Bush, R. I.; Hoeksema, J. T.; Aloise, J.; Bacon, L.; Burnette, A.;
De Forest, C.; Giles, P. M.; Leibrand, K.; Nigam, R.; Rubin, M.;
Scott, K.; Williams, S. D.; Basu, Sarbani; Christensen-Dalsgaard,
J.; Däppen, W.; Rhodes, E. J., Jr.; Duvall, T. L., Jr.; Howe, R.;
Thompson, M. J.; Gough, D. O.; Sekii, T.; Toomre, J.; Tarbell, T. D.;
Title, A. M.; Mathur, D.; Morrison, M.; Saba, J. L. R.; Wolfson,
C. J.; Zayer, I.; Milford, P. N.
1997IAUS..181..203K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Constraints on stellar interior physics from helioseismology.
Authors: Christensen-Dalsgaard, J.
1997IAUS..189..285C Altcode: 1998IAUS..189..285C; 1997astro.ph..2095C
The author uses as reference the so-called Model S of
Christensen-Dalsgaard et al. (1996). This, as well as other models
discussed here, were calibrated to present solar luminosity and radius,
as well as to the observed surface ratio Z<SUB>s</SUB>/X<SUB>s</SUB> =
0.0245 between the heavy-element and hydrogen abundances, by adjusting
the initial composition and the mixing-length parameter.
---------------------------------------------------------
Title: Three years of ANTENA: what we have done!
Authors: Belmonte, J. A.; Hernández, M. M.; Pérez Hernández, F.;
Vidal, I.; Roca Cortés, T.; Michel, E.; Auvergne, M.; Chevreton,
M.; Goupil, M. J.; Soufi, F.; Baglin, A.; Frandsen, S.; Viskum, M.;
Kjeldsen, H.; Christensen-Dalsgaard, J.; Schmider, F. X.; Fossat,
E.; Delache, Ph.; Provost, J.; Audard, N.; Berthomieu, G.; Paparó,
M.; Kovács, G.; Szabados, L.
1997IAUS..181..357B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On solar p-mode frequency shifts caused by near-surface
model changes
Authors: Christensen-Dalsgaard, J.; Thompson, M. J.
1997MNRAS.284..527C Altcode:
The effect on p-mode frequencies of changing the near-surface structure
of solar models is investigated. As is well known, changes confined
to the near-surface region have little effect on the low-frequency p
modes: this is as one would expect from a simple asymptotic description
which shows that these modes have upper turning points located well
beneath the photosphere. However, some examples of structural changes
show that, if the changes are viewed at fixed fractional radius (an
Eulerian description), the small frequency shifts at low frequency
come about through near-cancellation of different contributions which
are individually much larger than the resultant shifts themselves;
the reason is that even so-called near-surface changes extend
substantially below the upper turning points of these modes. We
demonstrate that the corresponding changes at fixed fractional mass
(a Lagrangian description) are confined much closer to the surface,
so that the small frequency shifts come about in a natural way.
---------------------------------------------------------
Title: The seismic structure of the Sun from GONG
Authors: Anderson, E.; Antia, H. M.; Basu, S.; Chaboyer, B.; Chitre,
S. M.; Christensen-Dalsgaard, J.; Eff-Darwich, A.; Elliott, J. R.;
Giles, P. M.; Gough, D. O.; Guzik, J. A.; Harvey, J. W.; Hill,
F.; Leibacher, J. W.; Kosovichev, A. G.; Monteiro, M. J. P. F. G.;
Richard, O.; Sekii, T.; Shibahashi, H.; Takata, M.; Thompson, M. J.;
Toomre, J.; Vauclair, S.; Vorontsov, S. V.
1997IAUS..181..151A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Improved solar models.
Authors: Chaboyer, B.; Basu, S.; Christensen-Dalsgaard, J.
1996JRASC..90..306C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Pulsation models of δ Scuti variables. I. The high-amplitude
double-mode stars.
Authors: Petersen, J. O.; Christensen-Dalsgaard, J.
1996A&A...312..463P Altcode:
The relations between high-amplitude δ Scuti stars and the much
more abundant low-amplitude δ Sct variables are not clear. Both
groups have similar periods and seem to have almost the same basic
physical properties, although their light-curve characteristics are
very different. In the last few years much improved observational data
have been published, and improved theoretical physics - in particular
the new OPAL/OP opacities - now allows much more accurate calculations
of theoretical evolution models including the normal-mode pulsation
frequencies. We here use new series of stellar envelope models to
give calibrations of the first overtone-to-fundamental mode and the
second-to-first overtone period ratios in terms of the primary model
parameters: metal content and mass-luminosity relation. Effects of
the secondary model parameters: hydrogen content, position within the
instability strip and assumed efficiency of convection are also studied
in detail, and shown to be small. These results combined with pulsation
analysis of new stellar evolution models are applied to discuss the
available information for double-mode high-amplitude δ Sct stars. We
conclude that observed period ratios and positions in the HR-diagram
are in agreement with the assumption that these variables are normal
stars following standard evolution. Observational data for SX Phoenicis
and AI Velorum are compared with theoretical evolution sequences. It
is shown that the photometry and the observed two periods of SX Phe
constrain the metal content to Z=0.001, the mass to 1.0 solar masses
and the bolometric magnitude to about 2.70mag. The inferred distance
of SX Phe gives a parallax of 0.012+/-0.002arcsec compared with that
of the HIPPARCOS Input Catalogue of 0.023+/-0.008arcsec. For AI Vel
the available photometry and the two primary observed periods do
not provide a unique solution. Models based on OPAL opacities allow
Z=0.01-0.02 with corresponding masses 1.6-2.0 solar masses. This can be
understood by the compensating effects from Z and the mass-luminosity
relation in the calibration of the period ratio. It is suggested that
the surprisingly narrow interval in the first overtone-to-fundamental
mode period ratio observed in the double-mode δ Sct stars may be due
to these compensating effects. Attempting to fit low-amplitude modes
observed in AI Vel in addition to the primary oscillations, it is
concluded that the present models cannot explain these oscillations in
terms of radial modes. The little understood relations between high-
and low-amplitude δ Sct stars are briefly discussed, and the problem
of mode identification is emphasized.
---------------------------------------------------------
Title: Asteroseismological calibration of open clusters
Authors: Audard, N.; Brown, T. M.; Christensen-Dalsgaard, J.; Frandsen,
S.; Kjeldsen, H.
1996BASI...24..305A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar structure as revealed by 1 year LOWL data
Authors: Basu, Sarbani; Christensen-Dalsgaard, J.; Schou, J.; Thompson,
M. J.; Tomczyk, S.
1996BASI...24..147B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An overview of the conference
Authors: Christensen-Dalsgaard, Jorgen
1996BASI...24..379C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Wave leakage in a magnetized isothermal atmosphere
Authors: Banerjee, Dipankar; Hasan, S. S.; Christensen-Dalsgaard, J.
1996BASI...24..325B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Effects on solar structure of opacity changes
Authors: Tripathy, S. C.; Christensen-Dalsgaard, J.
1996BASI...24..129T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: How are the observed frequencies related to solar structure?
Authors: Christensen-Dalsgaard, Jorgen
1996BASI...24..103C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Current State of Solar Modeling
Authors: Christensen-Dalsgaard, J.; Dappen, W.; Ajukov, S. V.;
Anderson, E. R.; Antia, H. M.; Basu, S.; Baturin, V. A.; Berthomieu,
G.; Chaboyer, B.; Chitre, S. M.; Cox, A. N.; Demarque, P.; Donatowicz,
J.; Dziembowski, W. A.; Gabriel, M.; Gough, D. O.; Guenther, D. B.;
Guzik, J. A.; Harvey, J. W.; Hill, F.; Houdek, G.; Iglesias, C. A.;
Kosovichev, A. G.; Leibacher, J. W.; Morel, P.; Proffitt, C. R.;
Provost, J.; Reiter, J.; Rhodes, E. J., Jr.; Rogers, F. J.; Roxburgh,
I. W.; Thompson, M. J.; Ulrich, R. K.
1996Sci...272.1286C Altcode:
Data from the Global Oscillation Network Group (GONG) project and
other helioseismic experiments provide a test for models of stellar
interiors and for the thermodynamic and radiative properties, on which
the models depend, of matter under the extreme conditions found in the
sun. Current models are in agreement with the helioseismic inferences,
which suggests, for example, that the disagreement between the predicted
and observed fluxes of neutrinos from the sun is not caused by errors in
the models. However, the GONG data reveal subtle errors in the models,
such as an excess in sound speed just beneath the convection zone. These
discrepancies indicate effects that have so far not been correctly
accounted for; for example, it is plausible that the sound-speed
differences reflect weak mixing in stellar interiors, of potential
importance to the overall evolution of stars and ultimately to estimates
of the age of the galaxy based on stellar evolution calculations.
---------------------------------------------------------
Title: Filtering out near-surface uncertainties from helioseismic
inversions
Authors: Basu, Sarbani; Christensen-Dalsgaard, J.; Perez Hernandez,
F.; Thompson, M. J.
1996MNRAS.280..651B Altcode:
The differences between observed solar p-mode frequencies and the
frequencies of a reference model can be inverted to infer the structure
of the Sun using a variety of linear inversion techniques. However, it
is well known that the adiabatic description, which is often employed
in frequency calculations, breaks down in the outermost layers of the
Sun. This and other uncertainties in the treatment of the superficial
layers introduce a slowly varying frequency-dependent function
into the frequency differences. <P />We present here a technique to
pre-process the frequency differences prior to applying any of the
standard inversion techniques in order to eliminate the frequency
dependent component which arises from the near-surface uncertainties,
suppressing also the corresponding contributions from the kernels
relating frequency differences to differences in structure. This
is achieved by applying suitable linear filters to the frequency
differences and to the mode kernels. We obtain the filtered kernels
and demonstrate that the surface contribution can be successfully
suppressed. We also present the results of the inversions performed
after the data and mode kernels have been filtered.
---------------------------------------------------------
Title: The Seismic Structure of the Sun
Authors: Gough, D. O.; Kosovichev, A. G.; Toomre, J.; Anderson,
E.; Antia, H. M.; Basu, S.; Chaboyer, B.; Chitre, S. M.;
Christensen-Dalsgaard, J.; Dziembowski, W. A.; Eff-Darwich, A.;
Elliott, J. R.; Giles, P. M.; Goode, P. R.; Guzik, J. A.; Harvey,
J. W.; Hill, F.; Leibacher, J. W.; Monteiro, M. J. P. F. G.; Richard,
O.; Sekii, T.; Shibahashi, H.; Takata, M.; Thompson, M. J.; Vauclair,
S.; Vorontsov, S. V.
1996Sci...272.1296G Altcode:
Global Oscillation Network Group data reveal that the internal
structure of the sun can be well represented by a calibrated standard
model. However, immediately beneath the convection zone and at the
edge of the energy-generating core, the sound-speed variation is
somewhat smoother in the sun than it is in the model. This could be a
consequence of chemical inhomogeneity that is too severe in the model,
perhaps owing to inaccurate modeling of gravitational settling or to
neglected macroscopic motion that may be present in the sun. Accurate
knowledge of the sun's structure enables inferences to be made about
the physics that controls the sun; for example, through the opacity,
the equation of state, or wave motion. Those inferences can then be
used elsewhere in astrophysics.
---------------------------------------------------------
Title: Differential Rotation and Dynamics of the Solar Interior
Authors: Thompson, M. J.; Toomre, J.; Anderson, E. R.; Antia, H. M.;
Berthomieu, G.; Burtonclay, D.; Chitre, S. M.; Christensen-Dalsgaard,
J.; Corbard, T.; De Rosa, M.; Genovese, C. R.; Gough, D. O.; Haber,
D. A.; Harvey, J. W.; Hill, F.; Howe, R.; Korzennik, S. G.; Kosovichev,
A. G.; Leibacher, J. W.; Pijpers, F. P.; Provost, J.; Rhodes, E. J.,
Jr.; Schou, J.; Sekii, T.; Stark, P. B.; Wilson, P. R.
1996Sci...272.1300T Altcode:
Splitting of the sun's global oscillation frequencies by large-scale
flows can be used to investigate how rotation varies with radius
and latitude within the solar interior. The nearly uninterrupted
observations by the Global Oscillation Network Group (GONG) yield
oscillation power spectra with high duty cycles and high signal-to-noise
ratios. Frequency splittings derived from GONG observations confirm
that the variation of rotation rate with latitude seen at the surface
carries through much of the convection zone, at the base of which is
an adjustment layer leading to latitudinally independent rotation at
greater depths. A distinctive shear layer just below the surface is
discernible at low to mid-latitudes.
---------------------------------------------------------
Title: Helioseismology, Solar Models and Solar Neutrinos
Authors: Christensen-Dalsgaard, Jørgen
1996NuPhS..48..325C Altcode:
Very accurate measurements of oscillation frequencies of the Sun
are providing detailed information about the structure of the solar
interior. Somewhat surprisingly, the results are in excellent agreement
with so-called 'standard solar models', provided up-to-date physics
is used and settling of helium and heavy elements is taken into
account. This suggests that an 'astrophysical solution' to the solar
neutrino problem may be unlikely.
---------------------------------------------------------
Title: Testing Solar Models with the GONG Data
Authors: Christensen-Dalsgaard, J.; Dappen, W.; Demarque, P.; GONG
Models Team
1996AAS...188.5302C Altcode: 1996BAAS...28..903C
The wealth of very precise data from the GONG network and other
helioseismic experiments provide a unique opportunity for testing the
modeling of stellar interiors. Stellar modeling forms the basis for
much of astrophysics. Furthermore, the application and calibration of
solar models to the helioseismic data provides a test of the physics
on which the models depend; thus we can investigate the thermodynamic
and radiative properties of matter under the extreme conditions
found in the Sun. Current models are in remarkable agreement with
the helioseismic inferences within the errors in the input data; this
suggests, for example, that the disagreement between the predicted and
observed fluxes of neutrinos from the Sun is unlikely to be caused
by errors in the standard solar model. However, careful analysis
of the GONG data reveals subtle discrepancies that we attribute to
uncertainties in some of the model input physics and the neglect of
other subtle physical processes. The role of mixing inside the Sun,
due for example to rotationally induced instabilities during its past
evolution, the precise form of the hydrogen depletion profile near the
center, the efficiency of helium and heavier element diffusion below
the convection zone, and the structure of the highly superadiabatic
layer just below the photosphere, are among the significant details in
solar models, which the high-quality GONG data will greatly help to
resolve. Comparisons between theoretical predictions of solar p-mode
frequencies, previous p-mode observations and the first GONG data are
used to illustrate these points.
---------------------------------------------------------
Title: The Sun's Hydrostatic Structure from LOWL Data
Authors: Basu, Sarbani; Christensen-Dalsgaard, J.; Schou, J.; Thompson,
M. J.; Tomczyk, S.
1996ApJ...460.1064B Altcode:
Recent observations with the LOWL (Low-Degree [l] Oscillations
Experiment) instrument have for the first time provided a uniform set of
frequencies that allow detailed inversion for the structure of much of
the Sun's deep interior. We present the results of inverting the LOWL
data and compare them with the corresponding results obtained using
inhomogeneous data sets from more than one instrument. Furthermore,
improvements in the description of the required physics motivates the
calculation of new solar models. Thus, we present results of inversions
of the LOWL data against several reference models using up-to-date
physics. In models including the gravitational settling of helium, the
sound speed and density agree with the Sun to within substantially
better than 1%. We test various modifications to the physics of
the models in order to see if the remaining small (but significant)
discrepancy between the Sun and the models can be removed. We find
that none of the modifications tested can adequately account for the
remaining discrepancy, though a small increase in helium diffusion
in the core gives a modest improvement over the standard diffusion
model. Finally, we find that the seismic data support theoretical
calculations that indicate that settling of heavier elements has
reduced the present surface value of Z by about 8% relative to its
mean interior value.
---------------------------------------------------------
Title: Seismic properties of the Sun's superadiabatic
layer. I. Theoretical modelling and parametrization of the
uncertainties.
Authors: Monteiro, M. J. P. F. G.; Christensen-Dalsgaard, J.; Thompson,
M. J.
1996A&A...307..624M Altcode:
Some alternatives to the traditional mixing-length theory (MLT)
have recently been proposed for modelling convective heat transport
inside stars. The ideal formulation is one that does not involve
any free parameters. However, in our present state of ignorance we
still need at least one free parameter in order to build solar models
with the correct radius. Having adjusted this parameter (e.g. the
mixing-length parameter α_c_) to obtain the observed radius, we cannot
discriminate non-seismically between different convective theories,
regardless of how low-efficiency convection is treated. In this paper
we consider how the additional information provided by global p-mode
frequencies can be used to investigate low-efficiency convection at
the top of the solar convective envelope and discriminate between
different theories. We consider a parametrization which in addition
to the mixing length has two further parameters: one (β_c_) which
regulates the relative degree of overadiabaticity (or inefficiency) of
convection, and a second (m) that affects the transition between the
regimes of efficient and inefficient convection. Our parametrization
includes traditional MLT__ and the theory of Canuto & Mazzitelli
as particular cases. We study the effect of varying these parameters
by constructing a series of envelope models with the same depth of
the convection zone and computing their oscillation frequencies. We
discuss our results in terms of kernels relating frequency changes to
changes in the structure of the superadiabatic region.
---------------------------------------------------------
Title: Filtering in Inversion for Solar Internal Structure
Authors: Basu, Sarbani; Christensen-Dalsgaard, J.; Pérez Hernández,
F.; Thompson, M. J.
1996imie.conf...32B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Choice of Trade-off Parameter in Helioseismic SOLA
Inversion
Authors: Stepanov, A. A.; Christensen-Dalsgaard, J.
1996imie.conf...54S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Testing a solar model: the forward problem.
Authors: Christensen-Dalsgaard, J.
1996stsu.conf...47C Altcode:
This paper addresses the forward problem, i.e., the relation between
the structure of a solar model and the corresponding frequencies. As
important, however, is the extent to which the frequencies reflect the
physics and other assumptions underlying the model calculation. Thus the
author considers some aspects of solar model computation. In addition,
the understanding of the diagnostic potential of the frequencies
requires information about the properties of the oscillations. He
investigates the relation between the properties of solar structure
and the oscillations by considering several examples of modifications
to the solar models and their effects on the frequencies and considers
further analyses of the observed frequencies. Finally, the prospects
of extending this type of work to other stars are addressed.
---------------------------------------------------------
Title: The interfacial F mode in a spherical solar model
Authors: Rosenthal, C. S.; Christensen-Dalsgaard, J.
1995MNRAS.276.1003R Altcode:
The solar f modes are a branch of oscillations characterized by a
close correspondence between their measured dispersion relation and
that predicted for a pure surface gravity wave: omega^2=gk where g
is the surface gravity of the Sun. However, there is now substantial
evidence for deviations from this simple behaviour. We consider the
hypothesis of Rosenthal & Gough that the f modes are characterized
better as an interfacial wave propagating at the chromosphere-corona
transition. Using a standard solar interior model, a semi-empirical
atmospheric model, and a parametrized transition region model as our
equilibrium state, we solve the linearized oscillation equations for
the interfacial f mode. We find that the frequencies of the interfacial
f mode differ from those of the classical f mode only at very high
degrees. We conclude that the interfacial f-mode theory may be the
correct explanation for the very high-degree data, but that some other
mechanism is required to explain the lower degree data.
---------------------------------------------------------
Title: The Influence of a Vertical Magnetic Field on Oscillations
in an Isothermal Stratified Atmosphere. II.
Authors: Banerjee, Dipankar; Hasan, S. S.; Christensen-Dalsgaard, J.
1995ApJ...451..825B Altcode:
We examine the effect of a uniform vertical magnetic field on the modes
of an isothermal stratified atmosphere. The present investigation is
a continuation of earlier work by Hasan & Christensen-Dalsgaard in
which this problem was studied for rigid boundary conditions. In this
paper, the earlier results are extended to different sets of boundary
conditions. We demonstrate explicitly how these boundary conditions
affect the various elementary wave modes present in the atmosphere. In
the weak-field limit, an analytic expression for the dispersion relation
is derived, which allows the effect of a weak magnetic field on the
modes to be studied. We show that, to lowest order in our perturbation
expansion, the oscillation spectrum can be analyzed in terms of (a) p-
and g-like modes; (b) a magnetic Lamb mode; (c) magnetic or slow modes;
and (d) a gravity- Lamb mode. The first three of these were present
in the previous analysis for rigid boundaries, whereas the last is
a consequence of the vertical gradients of the displacements at the
boundaries. We focus our attention on the properties of this mode and
show that it is present even in the moderate to strong field case as a
magnetogravity-Lamb mode. The recognition and physical interpretation
of this mode is a new feature of the present analysis. We also examine
the nature of the eigenfrequency curves in the diagnostic (or K-Ω)
diagram and find that, similar to the previous analysis, the modes
undergo avoided crossings. However, the nature of the solutions in
the present case is more complicated, especially when triple-mode
interactions occur. Furthermore, the connectivity of the curves in
the K-Ω diagram can be strongly influenced by the choice of boundary
conditions. Our results, though somewhat idealized, find application
in the analysis of waves in sunspots. It is conjectured that conditions
for the existence of the magnetogravity-Lamb mode may also be satisfied
in the subphotospheric layers of the Sun.
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Title: Helioseismic estimation of convective overshoot in the Sun
Authors: Christensen-Dalsgaard, Jorgen; Monteiro, Mario J. P. F. G.;
Thompson, Michael J.
1995MNRAS.276..283C Altcode:
By using the periodic signal present in the frequencies of
oscillation due to the base of the solar convection zone, Monteiro,
Christensen-Dalsgaard & Thompson gave an upper limit to the
extent of a layer of convective overshooting in the Sun. Alternative
studies have suggested that it may not be possible to do so since the
amplitude of the signal does not vary monotonically with the extent
of the layer. <P />In this work a new more complete set of models is
used to compare the values of the amplitude obtained from the fitting
of the signal with the expected amplitudes. These are determined using
the assumption that the rapid variation occurring at the base of the
convection zone and creating the periodic signal can be described as
discontinuities of the sound-speed derivatives. The amplitude of the
signal due to the discontinuity of the third derivative of the sound
speed is then proportional to the derivative of the radiative gradient,
while the amplitude resulting from the discontinuity of the second
derivative is proportional to the difference between radiative and
adiabatic gradients at the position where the transition occurs. The
latter is non-zero only if overshoot is present. <P />Asymptotic
predictions of the amplitudes of the signal in the p-mode frequencies
are in good agreement with the values found from fitting models with
substantial overshoot regions; as was also found by Monteiro et al.,
the observed solar frequencies place severe limits on the extent of
overshoot of this nature.
