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Author name code: roxburgh
ADS astronomy entries on 2022-09-14
author:"Roxburgh, Ian"
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Title: Inversions of Stellar Structure From Asteroseismic Data
Authors: Buldgen, Gaël; Bétrisey, Jérôme; Roxburgh, Ian W.;
Vorontsov, Sergei V.; Reese, Daniel R.
2022FrASS...9.2373B Altcode: 2022arXiv220611507B
The advent of space-based photometry missions in the early 21st century
enabled the application to asteroseismic data of advanced inference
techniques until then restricted to the field of helioseismology. The
high quality of the observations, the discovery of mixed modes in
evolved solar-like oscillators and the need for an improvement in the
determination of stellar fundamental parameters such as mass, radius
and age led to the development of sophisticated modelling tools,
amongst which seismic inversions play a key role. In this review,
we will discuss the existing inversion techniques for the internal
structure of distant stars adapted from helio-to asteroseismology. We
will present results obtained for various Kepler targets, their coupling
to other existing modelling techniques as well as the limitations
of seismic analyses and the perspectives for future developments of
these approaches in the context of the current TESS and the future
PLATO mission, as well as the exploitation of the mixed modes observed
in post-main sequence solar-like oscillators, for which variational
formulations might not provide sufficient accuracy.
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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: Mixed Modes and the Asteroseismic Surface Term
Authors: Ong, Joel J. M.; Basu, Sarbani; McKeever, Jean; Roxburgh, Ian;
Lund, Mikkel N.; Bieryla, Allyson; Viani, Lucas S.; Latham, David W.
2021plat.confE..43O Altcode:
We present new methodological developments regarding the treatment of
the asteroseismic surface term in stars with mixed modes. Models of
solar-like oscillators yield acoustic modes at different frequencies
than would be seen in actual stars possessing identical interior
structure, due to modelling error near the surface. This asteroseismic
“surface term” must be corrected when mode frequencies are used to
infer stellar structure. This is typically done by way of likelihood
functions intended to diagnose whether or not differences between
two sets of mode frequencies are consistent with a structural
perturbation localised to the stellar surface. Different choices of
these prescriptions modify the posterior distributions of fundamental
stellar properties — such as the mass, radius, and age — inferred
from individual stars using asteroseismology. These in turn induce
population-level systematic biases. Existing prescriptions developed for
p-modes are also not immediately applicable to the mixed modes seen in
more evolved solar-like oscillators. We examine some outstanding issues
in how the surface term is currently treated in stellar modelling
with asteroseismology, and how these new methods may address these
shortcomings, with a particular focus on the interaction between mode
mixing and these systematic effects.
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Title: Mixed Modes and Asteroseismic Surface Effects. I. Analytic
Treatment
Authors: Ong, J. M. Joel; Basu, Sarbani; Roxburgh, Ian W.
2021ApJ...920....8O Altcode: 2021ApJ...920....8J; 2021arXiv210703405O
Normal-mode oscillation frequencies computed from stellar models differ
from those that would be measured from stars with identical interior
structures because of modeling errors in the near-surface layers. These
frequency differences are referred to as the asteroseismic "surface
term." The vast majority of solar-like oscillators that have been
observed, and that are expected to be observed in the near future,
are evolved stars that exhibit mixed modes. For these evolved stars,
the inference of stellar properties from these mode frequencies has been
shown to depend on how this surface term is corrected for. We show that
existing parameterizations of the surface term account for mode mixing
only to first order in perturbation theory, if at all, and therefore
may not be adequate for evolved stars. Moreover, existing nonparametric
treatments of the surface term do not account for mode mixing. We derive
both a first-order construction and a more general approach for one
particular class of nonparametric methods. We illustrate the limits
of first-order approximations from both analytic considerations and
using numerical injection-recovery tests on stellar models. First-order
corrections for the surface term are strictly only applicable where
the size of the surface term is much smaller than both the coupling
strength between the mixed p and g modes, as well as the local g-mode
spacing. Our more general matrix construction may be applied to evolved
stars, where perturbation theory cannot be relied upon.
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Title: PBjam: A Python Package for Automating Asteroseismology of
Solar-like Oscillators
Authors: Nielsen, M. B.; Davies, G. R.; Ball, W. H.; Lyttle, A. J.;
Li, T.; Hall, O. J.; Chaplin, W. J.; Gaulme, P.; Carboneau, L.; Ong,
J. M. J.; García, R. A.; Mosser, B.; Roxburgh, I. W.; Corsaro, E.;
Benomar, O.; Moya, A.; Lund, M. N.
2021AJ....161...62N Altcode: 2020arXiv201200580N
Asteroseismology is an exceptional tool for studying stars using the
properties of observed modes of oscillation. So far the process of
performing an asteroseismic analysis of a star has remained somewhat
esoteric and inaccessible to nonexperts. In this software paper
we describe PBjam, an open-source Python package for analyzing
the frequency spectra of solar-like oscillators in a simple but
principled and automated way. The aim of PBjam is to provide a set of
easy-to-use tools to extract information about the radial and quadropole
oscillations in stars that oscillate like the Sun, which may then be
used to infer bulk properties such as stellar mass, radius, age, or even
structure. Asteroseismology and its data analysis methods are becoming
increasingly important as space-based photometric observatories are
producing a wealth of new data, allowing asteroseismology to be applied
in a wide range of contexts such as exoplanet, stellar structure and
evolution, and Galactic population studies. * Release 1.0.0 Zenodo,
doi:10.5281/zenodo.4300079.
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Title: TESS asteroseismology of the known planet host star
λ<SUP>2</SUP> Fornacis
Authors: Nielsen, M. B.; Ball, W. H.; Standing, M. R.; Triaud,
A. H. M. J.; Buzasi, D.; Carboneau, L.; Stassun, K. G.; Kane, S. R.;
Chaplin, W. J.; Bellinger, E. P.; Mosser, B.; Roxburgh, I. W.; Çelik
Orhan, Z.; Yıldız, M.; Örtel, S.; Vrard, M.; Mazumdar, A.; Ranadive,
P.; Deal, M.; Davies, G. R.; Campante, T. L.; García, R. A.; Mathur,
S.; González-Cuesta, L.; Serenelli, A.
2020A&A...641A..25N Altcode: 2020arXiv200700497N
Context. The Transiting Exoplanet Survey Satellite (TESS) is observing
bright known planet-host stars across almost the entire sky. These
stars have been subject to extensive ground-based observations,
providing a large number of radial velocity measurements. <BR />
Aims: The objective of this work is to use the new TESS photometric
observations to characterize the star <ASTROBJ>λ2 Fornacis</ASTROBJ>,
and following this to update the parameters of the orbiting planet
<ASTROBJ>λ2 For b</ASTROBJ>. <BR /> Methods: We measured the
frequencies of the p-mode oscillations in <ASTROBJ>λ2 For</ASTROBJ>,
and in combination with non-seismic parameters estimated the stellar
fundamental properties using stellar models. Using the revised
stellar properties and a time series of archival radial velocities
from the UCLES, HIRES and HARPS instruments spanning almost 20 years,
we refit the orbit of λ<SUP>2</SUP> For b and searched the residual
radial velocities for remaining variability. <BR /> Results: We find
that λ<SUP>2</SUP> For has a mass of 1.16 ± 0.03 M<SUB>⊙</SUB>
and a radius of 1.63 ± 0.04 R<SUB>⊙</SUB>, with an age of 6.3 ±
0.9 Gyr. This and the updated radial velocity measurements suggest a
mass of λ<SUP>2</SUP> For b of 16.8<SUB>-1.3</SUB><SUP>+1.2</SUP>
M<SUB>⊕</SUB>, which is ∼5M<SUB>⊕</SUB> less than literature
estimates. We also detect an additional periodicity at 33 days in the
radial velocity measurements, which is likely due to the rotation of the
host star. <BR /> Conclusions: While previous literature estimates of
the properties of λ<SUP>2</SUP> For are ambiguous, the asteroseismic
measurements place the star firmly at the early stage of its subgiant
evolutionary phase. Typically only short time series of photometric
data are available from TESS, but by using asteroseismology it is still
possible to provide tight constraints on the properties of bright
stars that until now have only been observed from the ground. This
prompts a reexamination of archival radial velocity data that have
been accumulated in the past few decades in order to update the
characteristics of the planet hosting systems observed by TESS for
which asteroseismology is possible.
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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.
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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).
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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.
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Title: Overfitting and correlations in model fitting with separation
ratios
Authors: Roxburgh, Ian W
2018arXiv180807556R Altcode:
The $r_{01}$ and $r_{10}$ separation ratios are not independent so
combing them into a single series $r_{010}$ is overfitting the data,
this can lead to almost singular covariance matrices with very large
condition numbers, and hence to spurious results when comparing models
and observations. Since the $r_{02}$ ratios are strongly correlated
with $r_{10}$ and $r_{01}$ ratios, they should be combined into a
single series $r_{102}$ (or $r_{012}$), which are not overfitted, and
models and observation compared using the covariance matrix $cov_{102}$
(or $cov_{012}$) of the combined set. I illustrate these points by
comparing the revised Legacy Project data with my results on the 10
Kepler stars in common.
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Title: Anomalies in the Kepler Asteroseismic Legacy Project Data A
re-analysis of 16 Cyg A & B, KIC 8379927 and 6 solar-like stars
Authors: Roxburgh, Ian W.
2017A&A...604A..42R Altcode: 2017arXiv170604408R
I compare values of the frequencies, separation ratios, errors and
covariance matrices from a new analysis of 9 solar-like stars with
the Legacy project values reported by Lund et al and, for 16Cyg
A&B and KIC 8379927, with values derived by Davies et al. There
is good agreement between my results and Davies's for these 3 stars,
but no such agreement with the Legacy project results. My frequencies
differ from the Legacy values, there are inconsistencies in the Legacy
frequency covariance matrices which are not positive definite, and the
Legacy errors on separation ratios are up to 40 times larger than mine
and the values and upper limits derived from the Legacy frequency
covariances. There are similar anomalies for 6 other solar-like
stars: frequencies and separation ratio errors disagree and 2 have
non positive definite covariance matrices. There are inconsistencies
in the covariance matrices of 27 the 66 stars in the full Legacy set
and problems with the ratio errors for the vast majority of these stars.
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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: Using red clump stars to correct the Gaia DR1 parallaxes
Authors: Davies, Guy R.; Lund, Mikkel N.; Miglio, Andrea; Elsworth,
Yvonne; Kuszlewicz, James S.; North, Thomas S. H.; Rendle, Ben;
Chaplin, William J.; Rodrigues, Thaíse S.; Campante, Tiago L.;
Girardi, Léo; Hale, Steven J.; Hall, Oliver; Jones, Caitlin D.;
Kawaler, Steven D.; Roxburgh, Ian; Schofield, Mathew
2017A&A...598L...4D Altcode: 2017arXiv170102506D
Recent results have suggested that there is tension between the Gaia DR1
TGAS distances and the distances obtained using luminosities determined
by eclipsing binaries or asteroseismology on red giant stars. We use
the K<SUB>s</SUB>-band luminosities of red clump stars, identified
and characterized by asteroseismology, to make independent distance
estimates. Our results suggest that Gaia TGAS distances contain a
systematic error that decreases with increasing distance. We propose
a correction to mitigate this offset as a function of parallax that
is valid for the Kepler field and values of parallax that are less
than 1.6 mas. For parallaxes greater than this, we find agreement with
previously published values. We note that the TGAS distances to the red
clump stars of the open cluster M67 show a high level of disagreement
that is difficult to correct for.
---------------------------------------------------------
Title: A new asteroseismic diagnostic for internal rotation in γ
Doradus stars
Authors: Ouazzani, Rhita-Maria; Salmon, S. J. A. J.; Antoci, V.;
Bedding, T. R.; Murphy, S. J.; Roxburgh, I. W.
2017MNRAS.465.2294O Altcode: 2016arXiv161006184O
With four years of nearly continuous photometry from Kepler,
we are finally in a good position to apply asteroseismology to γ
Doradus stars. In particular, several analyses have demonstrated the
possibility to detect non-uniform period spacings, which have been
predicted to be directly related to rotation. In this paper, we define
a new seismic diagnostic for rotation in γ Doradus stars which are
too rapidly rotating to present rotational splittings. Based on the
non-uniformity of their period spacings, we define the observable
Σ as the slope of the period spacing when plotted as a function of
period. We provide a one-to-one relation between this observable Σ
and the internal rotation, which applies widely in the instability
strip of γ Doradus stars. We apply the diagnostic to a handful of
stars observed by Kepler. Thanks to g modes in γ Doradus stars, we
are now able to determine the internal rotation of stars on the lower
main sequence, which is still not possible for Sun-like stars.
---------------------------------------------------------
Title: 16CygA&B and Kepler Legacy values : Differences between
the values of frequencies by different fitters
Authors: Roxburgh, Ian W
2016arXiv160900568R Altcode:
The differences between the oscillation frequencies and uncertainty
estimates of a star derived by different fitters can be large,
sufficiently large so that, were one to find a stellar model that fitted
one frequency set ($\chi^2\sim 1$), it does not fit an alternative
set. I give 21 examples, comparing frequency sets in common between the
Kepler Legacy project and frequency sets from Appourchaux et al (2014)
and Davies et al (2015). For 16CygA&B the differences are large;
the $\chi^2$ of the fit of Legacy to Davies's values ranging from 1.64
to 11.47 for 16CygA and 1.62 to 1.79 for 16CygB, depending on which
error estimates are used. I analyse both stars in some detail applying
my own mode fitting code to both the Legacy and Davies's power spectra
and find reasonable agreement with Davies's full frequency sets and
very good agreement between values for modes with signal/noise > 1
($\chi^2 = 0.06, \chi^2_B=0.03$). But the difference with the Legacy
values remains large even for modes with S/N>1. I also examine the
effects of different power spectra (weighted and unweighted) using
the kasoc light curves for Q6-17.2 and Q7-Q16, the effect of different
mode height ratios and different rotational splitting and inclination.
---------------------------------------------------------
Title: Asteroseismic model fitting by comparing ɛ<SUB>nℓ</SUB>
values (Corrigendum)
Authors: Roxburgh, Ian W.
2016A&A...586C...2R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: I.2 Seeds take root in Europe
Authors: Fridlund, M.; Roxburgh, I.; CoRot Team
2016cole.book....7F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Asteroseismic model fitting by comparing ɛ<SUB>nℓ</SUB>
values
Authors: Roxburgh, Ian W.
2016A&A...585A..63R Altcode:
We present an asteroseismic model fitting algorithm based on
comparing model and observed ɛ<SUB>ℓ</SUB>(ν) values defined
in terms of frequencies by ν<SUB>nℓ</SUB> = Δ [ n + ℓ/ 2 +
ɛ<SUB>ℓ</SUB>(ν<SUB>nℓ</SUB>) ] where Δ is an average large
separation. We show that if two stellar models have the same interior
structure but different outer layers then the difference between their
ɛ<SUB>ℓ</SUB>(ν) values, interpolated to the same frequencies,
collapses to a function only of frequency, independent of angular
degree ℓ. The algorithm tests the goodness fit by comparing the
difference in model and observed ɛ values after having subtracted
off a best fit ℓ independent function of frequency ℱ(ν), and
only requires interpolation in model values and not in observed
values so the errors on the observed values are uncorrelated; it
is independent of the n values assigned to the radial ordering of
the frequencies and does not require the calculation of inner phase
shifts of the model. We contrast this to a proposed direct frequency
matching technique which minimises the difference between observed and
model frequencies after having subtracted off an ℓ independent fit
to these differences. We show this technique is flawed in principle,
that all models with the same dimensionless structure but any mass
and radius have the same quality of fit to an observed data set,
and that it can give erroneous best fit models. We illustrate the
epsilon matching technique by comparing stellar models and then apply
it to data on HD 177153 (aka Perky). On comparing observations with
a set of main sequence evolutionary models we find that models which
satisfy constraints on the luminosity, radius, Δ, and on ɛ matching,
have masses in the range 1.155 ± 0.035 M<SUB>⊙</SUB> and ages in the
range 4.486 ± 0.250 × 10<SUP>9</SUP> yr. Since the large separation
and the radius are surface layer dependent we examine "pure surface
layer independent" model fitting where the only constraints on the
model fitting are on the luminosity and epsilon matching, and show that
the best fit models have M/M<SUB>⊙</SUB> = 1.13 ± 0.06 and age =
4.62 ± 0.39 × 10<SUP>9</SUP> yr.
---------------------------------------------------------
Title: Scaled models, scaled frequencies, and model fitting
Authors: Roxburgh, Ian W.
2015A&A...584A..71R Altcode:
I show that given a model star of mass M, radius R, and density
profile ρ(x) [x = r/R], there exists a two parameter family
of models with masses M<SUB>k</SUB>, radii R<SUB>k</SUB>,
density profile ρ<SUB>k</SUB>(x) = λρ(x) and frequencies
ν<SUP>k</SUP><SUB>nℓ</SUB> = λ<SUP>1/2</SUP>ν<SUB>nℓ</SUB>, where
λ,R<SUB>k</SUB>/R<SUB>A</SUB> are scaling factors. These models have
different internal structures, but all have the same value of separation
ratios calculated at given radial orders n, and all exactly satisfy
a frequency matching algorithm with an offset function determined as
part of the fitting procedure. But they do not satisfy ratio matching
at given frequencies nor phase shift matching. This illustrates that
erroneous results may be obtained when model fitting with ratios at
given n values or frequency matching. I give examples from scaled
models and from non scaled evolutionary models.
---------------------------------------------------------
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: A note on the use of surface offset corrections in
asteroseismic model fitting
Authors: Roxburgh, Ian W.
2015A&A...581A..58R Altcode:
We critically investigate the practice of adding a power-law surface
offset correction f(ν) to the frequencies of stellar models prior
to seeking best fit models to an observed star. We show that surface
layer independent indicators of the internal structure, phase shifts
and separation ratios, are displaced in frequency by f(ν) and are
therefore not the same as those of the model. Consequently such
best fit models do not have exactly the same interior structure as
the observed star. Using results on the star HD 177153 we show that
the difference between observed and model frequencies for best fit
models obtained using surface layer independent procedures have a
wide range of different offsets which do not in general follow a
Kjeldsen-like power law, and further that best fit models obtained
using the offset correction procedure do not necessarily satisfy
surface layer independent constraints on the internal structure.
---------------------------------------------------------
Title: Pulsations of rapidly rotating stars. II. Realistic modelling
for intermediate-mass stars
Authors: Ouazzani, R. -M.; Roxburgh, I. W.; Dupret, M. -A.
2015A&A...579A.116O Altcode: 2015arXiv150501088O
Context. Very high precision seismic space missions such as CoRoT
and Kepler provide the means for testing the modelling of transport
processes in stellar interiors. For some stars, such as δ Scuti,
γ Doradus, and Be stars, the observed pulsation spectra are
modified by rotation to such an extent that it prevents any fruitful
interpretation. <BR /> Aims: Our aim is to characterise acoustic
pulsation spectra of realistic stellar models in order to be able to
interpret asteroseismic data from such stars. <BR /> Methods: The 2D
oscillation code ACOR, which treats rotation in a non-perturbative
manner, is used to study pulsation spectra of highly distorted evolved
models of stars. Two-dimensional models of stars are obtained by a
self-consistent method that distorts spherically averaged stellar
models a posteriori, at any stage of evolution, and for any type of
rotation law. <BR /> Results: Four types of modes are calculated in
a very dense frequency spectrum, among which are island modes. The
regularity of the island modes spectrum is confirmed and yields a
new set of quantum numbers, with which an échelle diagram can be
built. Mixed gravito-acoustic modes are calculated in rapidly rotating
models for the first time.
---------------------------------------------------------
Title: Surface layer independent model fitting by phase matching:
theory and application to HD 49933 and HD 177153 (aka Perky)
Authors: Roxburgh, Ian W.
2015A&A...574A..45R Altcode: 2014arXiv1406.6491R
<BR /> Aims: Our aim is to describe the theory of surface layer
independent model fitting by phase matching and to apply this to the
stars HD 49933 observed by CoRoT, and HD 177153 (aka Perky) observed
by Kepler. <BR /> Methods: We use theoretical analysis, phase shifts,
and model fitting. <BR /> Results: We define the inner and outer phase
shifts of a frequency set of a model star and show that the outer phase
shifts are (almost) independent of degree ℓ, and that a function
of the inner phase shifts (the phase function) collapses to an ℓ
independent function of frequency in the outer layers. We then show how
to use this result in a model fitting technique to find a best fit model
to an observed frequency set by calculating the inner phase shifts of
a model using the observed frequencies and determining the extent to
which the phase function collapses to a single function of frequency in
the outer layers. This technique does not depend on the radial order
n assigned to the observed frequencies. We give two examples applying
this technique to the frequency sets of HD 49933 observed by CoRoT and
HD 177153 (aka Perky) observed by Kepler, for which measurements of
angular diameters and bolometric fluxes are available. For HD 49933
we find a very wide range of models to be consistent with the data
(all with convective core overshooting) - and conclude that the data is
not precise enough to make any useful restrictions on the structure of
this star. For HD 177153 our best fit models have no convective cores,
masses in the range 1.15-1.17 M<SUB>⊙</SUB>, ages of 4.45-4.70 ×
10<SUP>9</SUP> yr, Z in the range 0.021-0.024, XH = 0.71-0.72, Y =
0.256 - 0.266 and mixing length parameter α = 1.8. We compare our
results to those of previous studies. We contrast the phase matching
technique to that using the ratios of small to large separations,
showing that it avoids the problem of correlated errors in separation
ratio fitting and of assigning radial order n to the modes.
---------------------------------------------------------
Title: On the use of the average large separation in surface layer
independent model fitting and mass estimation
Authors: Roxburgh, Ian W.
2014A&A...571A..88R Altcode: 2014arXiv1406.1997R
The physics of the outer layers of a star are not well understood but
these layers make a major contribution to the large separation. We
quantify this using stellar models and show that the contribution
ranges from 6% from the outer 0.1% of the radius to 30% from the outer
5%; it would therefore be inconsistent to impose the large separation
as a constraint on surface layer independent model fitting. The mass
and luminosity are independent of the outer layers and can be used as
constraints, the mass being determined from binarity or from surface
gravity and radius. The radius can be used as a constraint but with
enhanced error estimates. Using stellar models we show that the errors
in estimating mass from the scaling relation between mass, radius and
large separation can be up to 30%, and that the errors are not reduced
on using the asymptotic value of the large separation estimated by
extrapolation to high frequencies.
---------------------------------------------------------
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: Seismic analysis of HD 43587Aa, a solar-like oscillator in
a multiple system
Authors: Boumier, P.; Benomar, O.; Baudin, F.; Verner, G.; Appourchaux,
T.; Lebreton, Y.; Gaulme, P.; Chaplin, W.; García, R. A.; Hekker,
S.; Regulo, C.; Salabert, D.; Stahn, T.; Elsworth, Y.; Gizon, L.;
Hall, M.; Mathur, S.; Michel, E.; Morel, T.; Mosser, B.; Poretti,
E.; Rainer, M.; Roxburgh, I.; do Nascimento, J. -D., Jr.; Samadi,
R.; Auvergne, M.; Chaintreuil, S.; Baglin, A.; Catala, C.
2014A&A...564A..34B Altcode: 2014arXiv1402.5053B
Context. The object HD 43587Aa is a G0V star observed during the
145-day LRa03 run of the COnvection, ROtation and planetary Transits
space mission (CoRoT), for which complementary High Accuracy Radial
velocity Planet Searcher (HARPS) spectra with S/N > 300 were also
obtained. Its visual magnitude is 5.71, and its effective temperature is
close to 5950 K. It has a known companion in a highly eccentric orbit
and is also coupled with two more distant companions. <BR /> Aims:
We undertake a preliminary investigation of the internal structure
of HD 43587Aa. <BR /> Methods: We carried out a seismic analysis of
the star, using maximum likelihood estimators and Markov chain Monte
Carlo methods. <BR /> Results: We established the first table of the
eigenmode frequencies, widths, and heights for HD 43587Aa. The star
appears to have a mass and a radius slightly larger than the Sun, and is
slightly older (5.6 Gyr). Two scenarios are suggested for the geometry
of the star: either its inclination angle is very low, or the rotation
velocity of the star is very low. <BR /> Conclusions: A more detailed
study of the rotation and of the magnetic and chromospheric activity for
this star is needed, and will be the subject of a further study. New
high resolution spectrometric observations should be performed for at
least several months in duration.
---------------------------------------------------------
Title: Seismological Diagnostics for Solar-like Stars
Authors: Roxburgh, Ian W
2014arXiv1402.1391R Altcode:
The oscillations in solar like stars are described in terms of the
phase shifts of the eigenmodes from simple sine-waves. We discuss
model fitting and inversion techniques based on this representation. We
analyse the periodic signatures from the HeII ionisation zone and base
of the convective envelope of the CoRoT star HD49933.
---------------------------------------------------------
Title: Asteroseismic Analysis of the CoRoT Target HD 169392
Authors: Mathur, S.; Bruntt, H.; Catala, C.; Benomar, O.; Davies,
G. R.; García, R. A.; Salabert, D.; Ballot, J.; Mosser, B.; Régulo,
C.; Chaplin, W. J.; Elsworth, Y.; Handberg, R.; Hekker, S.; Mantegazza,
L.; Michel, E.; Poretti, E.; Rainer, M.; Roxburgh, I. W.; Samadi,
R.; Steslicki, M.; Uytterhoeven, K.; Verner, G. A.; Auvergne, M.;
Baglin, A.; Barceló Forteza, S.; Baudin, F.; Roca Cortés, T.
2013ASPC..479..155M Altcode: 2013arXiv1308.0647M
The satellite CoRoT (Convection, Rotation, and planetary Transits)
has provided high-quality data for almost six years. We show here
the asteroseismic analysis and modeling of HD 169392A, which belongs
to a weakly-bound binary system as the distance between the two
components is ∼4250 au. The main component, HD 169392A, is a G0 IV
star with a magnitude of 7.50 while the second component is a G0 V -
G2 IV star with a magnitude of 8.98. This analysis focuses on the
main component, as the secondary is too faint for the measurement of
seismic parameters. A complete modeling has been possible thanks to
complementary spectroscopic observations from HARPS (High Accuracy
Radial Velocity Planet Searcher), providing T<SUB>eff</SUB> = 5985 ±
60 K, log g = 3.96 ± 0.07, and [Fe/H] = -0.04 ± 0.10.
---------------------------------------------------------
Title: On the use of the ratio of small to large separations in
asteroseismic model fitting
Authors: Roxburgh, Ian W.; Vorontsov, Sergei V.
2013A&A...560A...2R Altcode: 2013arXiv1307.5069R
<BR /> Aims: We aim to show that model fitting by searching for a best
fit of observed and model separation ratios at the same radial orders
n is in principle incorrect, and to show that a correct procedure is to
compare the model ratios interpolated to the observed frequencies. <BR
/> Methods: We compare models with different interior structures and
outer layers, relate the separation ratios to phase shift differences,
conduct model fitting experiments using separation ratios, and relate
phase shift differences to internal phase shifts. <BR /> Results:
We show that the separation ratios of stellar models with the same
interior structure, but different outer layers, are not the same when
compared at the same radial order n, but are the same when evaluated
at the same frequencies by interpolation. The separation ratios trace
the phase shift differences as a function of frequency, not of n, and
it is the phase shift differences which are determined by the interior
structure. We give examples from model fitting where the ratios at the
same n values agree but the models have different interior structure,
and where the ratios agree when interpolated to the same frequencies
and the models have the same interior structure. The correct procedure
is to compare observed ratios with model values interpolated to the
observed frequencies.
---------------------------------------------------------
Title: Seismic constraints on rotation of Sun-like star and mass
of exoplanet
Authors: Gizon, L.; Ballot, J.; Michel, E.; Stahn, T.; Vauclair, G.;
Bruntt, H.; Quirion, P. -O.; Benomar, O.; Vauclair, S.; Appourchaux,
T.; Auvergne, M.; Baglin, A.; Barban, C.; Baudin, F.; Bazot, M.;
Campante, T.; Catala, C.; Chaplin, W.; Creevey, O.; Deheuvels, S.;
Dolez, N.; Elsworth, Y.; Garcia, R.; Gaulme, P.; Mathis, S.; Mathur,
S.; Mosser, B.; Regulo, C.; Roxburgh, I.; Salabert, D.; Samadi, R.;
Sato, K.; Verner, G.; Hanasoge, S.; Sreenivasan, K. R.
2013PNAS..11013267G Altcode: 2013arXiv1308.4352G
Rotation is thought to drive cyclic magnetic activity in the Sun
and Sun-like stars. Stellar dynamos, however, are poorly understood
owing to the scarcity of observations of rotation and magnetic fields
in stars. Here, inferences are drawn on the internal rotation of a
distant Sun-like star by studying its global modes of oscillation. We
report asteroseismic constraints imposed on the rotation rate and the
inclination of the spin axis of the Sun-like star HD 52265, a principal
target observed by the CoRoT satellite that is known to host a planetary
companion. These seismic inferences are remarkably consistent with an
independent spectroscopic observation (rotational line broadening)
and with the observed rotation period of star spots. Furthermore,
asteroseismology constrains the mass of exoplanet HD 52265b. Under
the standard assumption that the stellar spin axis and the axis of the
planetary orbit coincide, the minimum spectroscopic mass of the planet
can be converted into a true mass of 1.85 (+0.52,-0.42) M_Jupiter,
which implies that it is a planet, not a brown dwarf.
---------------------------------------------------------
Title: Solar-like oscillations in distant stars as seen by CoRoT :
the special case of HD 42618, a solar sister
Authors: Barban, C.; Deheuvels, S.; Goupil, M. J.; Lebreton, Y.;
Mathur, S.; Michel, E.; Morel, Th; Ballot, J.; Baudin, F.; Belkacem,
K.; Benomar, O.; Boumier, P.; Davies, G. R.; García, R. A.; Hall,
M. P.; Mosser, B.; Poretti, E.; Régulo, C.; Roxburgh, I.; Samadi,
R.; Verner, G.; CoRoT Team
2013JPhCS.440a2030B Altcode:
We report the observations of a main-sequence star, HD 42618
(T<SUB>eff</SUB> = 5765 K, G3V) by the space telescope CoRoT. This
is the closest star to the Sun ever observed by CoRoT in term of its
fundamental parameters. Using a preliminary version of CoRoT light
curves of HD 42618, p modes are detected around 3.2 mHz associated
to l = 0, 1 and 2 modes with a large spacing of 142 μHz. Various
methods are then used to derive the mass and radius of this star
(scaling relations from solar values as well as comparison between
theoretical and observationnal frequencies) giving values in the range
of (0.80 - 1.02)M<SUB>solar</SUB> and (0.91 - 1.01)R<SUB>solar</SUB>. A
preliminary analysis of l = 0 and 1 modes allows us also to study the
amount of penetrative convection at the base of the convective envelope.
---------------------------------------------------------
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: Pulsations of rapidly rotating evolved stars
Authors: Ouazzani, R-M.; Roxburgh, I. W.; Dupret, M-A
2013arXiv1301.2496O Altcode:
A new two dimensional non-perturbative code to compute accurate
oscillation modes of rapidly rotating stars is presented. The 2D
calculations fully take into account the centrifugal distorsion of the
star while the non perturbative method includes the full influence
of the Coriolis acceleration. This 2D non-perturbative code is used
to study pulsational spectra of highly distorted evolved models of
stars. 2D models of stars are obtained by a self consistent method
which distorts spherically averaged stellar models a posteriori. We
are also able to compute gravito-acoustic modes for the first time in
rapidly rotating stars. We present the dynamics of pulsation modes in
such models, and show regularities in their frequency spectra.
---------------------------------------------------------
Title: Study of HD 169392A observed by CoRoT and HARPS
Authors: Mathur, S.; Bruntt, H.; Catala, C.; Benomar, O.; Davies,
G. R.; García, R. A.; Salabert, D.; Ballot, J.; Mosser, B.; Régulo,
C.; Chaplin, W. J.; Elsworth, Y.; Handberg, R.; Hekker, S.; Mantegazza,
L.; Michel, E.; Poretti, E.; Rainer, M.; Roxburgh, I. W.; Samadi,
R.; Stȩślicki, M.; Uytterhoeven, K.; Verner, G. A.; Auvergne, M.;
Baglin, A.; Barceló Forteza, S.; Baudin, F.; Roca Cortés, T.
2013A&A...549A..12M Altcode: 2012arXiv1209.5696M
Context. The results obtained by asteroseismology with data from
space missions such as CoRoT and Kepler are providing new insights
into stellar evolution. After five years of observations, CoRoT
is continuing to provide high-quality data and we here present an
analysis of the CoRoT observations of the double star HD 169392,
complemented by ground-based spectroscopic observations. <BR /> Aims:
This work aims at characterising the fundamental parameters of the two
stars, their chemical composition, the acoustic-mode global parameters
including their individual frequencies, and their dynamics. <BR />
Methods: We analysed HARPS observations of the two stars to derive
their chemical compositions. Several methods were used and compared
to determine the global properties of stars' acoustic modes and their
individual frequencies from the photometric data of CoRoT. <BR />
Results: The new spectroscopic observations and archival astrometric
values suggest that HD 169392 is a weakly bound wide binary system. We
obtained spectroscopic parameters for both components which suggest
that they originate from the same interstellar cloud. However, only
the signature of oscillation modes of HD 169392 A was measured;
the signal-to-noise ratio of the modes in HD 169392B is too low
to allow any confident detection. For HD 169392 A we were able to
extract parameters of modes for ℓ = 0, 1, 2, and 3. The analysis
of splittings and inclination angle gives two possible solutions: one
with with splittings and inclination angles of 0.4-1.0 μHz and 20 -
40°, the other with 0.2-0.5 μHz and 55-86°. Modelling this star
using the Asteroseismic Modeling Portal (AMP) gives a mass of 1.15
± 0.01 M<SUB>⊙</SUB>, a radius of 1.88 ± 0.02 R<SUB>⊙</SUB>,
and an age of 4.33 ± 0.12 Gyr. The uncertainties come from estimated
errors on the observables but do not include uncertainties on the
surface layer correction or the physics of stellar models. <P />The
CoRoT space mission, launched on December 27 2006, has been developed
and is operated by CNES, with the contribution of Austria, Belgium,
Brazil, ESA (RSSD and Science Programme), Germany and Spain.This
work is based on ground-based observations made with the ESO 3.6
m-telescope at La Silla Observatory under the ESO Large Programme
LP185-D.0056.Tables 5 and 7 are available in electronic form at <A
href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Pulsations of an Evolved Self-consistently Distorted Star
Authors: Ouazzani, R. -M.; Dupret, M. -A.; Roxburgh, I. W.; Goupil,
M. -J.
2012ASPC..462..402O Altcode:
A new two-dimensional (2D) non-perturbative method to compute accurate
oscillation modes of rapidly rotating stars is presented. The 2D
calculations fully take into account the centrifugal distortion of the
star while the non-perturbative method includes the full influence
of the Coriolis acceleration, and are used to compute oscillation
modes of rapid rotators — high-order p-modes in δ Scuti stars, as
well as low-order p- and g-modes in β Cephei stars. We compare the
oscillation spectra obtained for centrifugally distorted polytropes
with those of Reese et al. (2006), and give the first results for a
realistic 2D model of a rapidly rotating 2 M<SUB>⊙</SUB> evolved
star computed with the method developed by Roxburgh (2006).
---------------------------------------------------------
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: 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: 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: Global asteroseismic properties of solar-like oscillations
observed by Kepler: a comparison of complementary analysis methods
Authors: Verner, G. A.; Elsworth, Y.; Chaplin, W. J.; Campante,
T. L.; Corsaro, E.; Gaulme, P.; Hekker, S.; Huber, D.; Karoff, C.;
Mathur, S.; Mosser, B.; Appourchaux, T.; Ballot, J.; Bedding, T. R.;
Bonanno, A.; Broomhall, A. -M.; García, R. A.; Handberg, R.; New,
R.; Stello, D.; Régulo, C.; Roxburgh, I. W.; Salabert, D.; White,
T. R.; Caldwell, D. A.; Christiansen, J. L.; Fanelli, M. N.
2011MNRAS.415.3539V Altcode: 2011MNRAS.tmp..892V; 2011arXiv1105.0571V
We present the asteroseismic analysis of 1948 F-, G- and K-type
main-sequence and subgiant stars observed by the National Aeronautics
and Space Administration Kepler mission. We detect and characterize
solar-like oscillations in 642 of these stars. This represents the
largest cohort of main-sequence and subgiant solar-like oscillators
observed to date. The photometric observations are analysed using the
methods developed by nine independent research teams. The results are
combined to validate the determined global asteroseismic parameters
and calculate the relative precision by which the parameters can be
obtained. We correlate the relative number of detected solar-like
oscillators with stellar parameters from the Kepler Input Catalogue
and find a deficiency for stars with effective temperatures in the
range 5300 ≲T<SUB>eff</SUB>≲ 5700 K and a drop-off in detected
oscillations in stars approaching the red edge of the classical
instability strip. We compare the power-law relationships between the
frequency of peak power, ν<SUB>max</SUB>, the mean large frequency
separation, Δν, and the maximum mode amplitude, A<SUB>max</SUB>,
and show that there are significant method-dependent differences in the
results obtained. This illustrates the need for multiple complementary
analysis methods to be used to assess the robustness and reproducibility
of results derived from global asteroseismic parameters.
---------------------------------------------------------
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: Accurate p-mode measurements of the G0V metal-rich CoRoT
target HD 52265
Authors: Ballot, J.; Gizon, L.; Samadi, R.; Vauclair, G.; Benomar, O.;
Bruntt, H.; Mosser, B.; Stahn, T.; Verner, G. A.; Campante, T. L.;
García, R. A.; Mathur, S.; Salabert, D.; Gaulme, P.; Régulo, C.;
Roxburgh, I. W.; Appourchaux, T.; Baudin, F.; Catala, C.; Chaplin,
W. J.; Deheuvels, S.; Michel, E.; Bazot, M.; Creevey, O.; Dolez, N.;
Elsworth, Y.; Sato, K. H.; Vauclair, S.; Auvergne, M.; Baglin, A.
2011A&A...530A..97B Altcode: 2011arXiv1105.3551B
Context. The star <ASTROBJ>HD 52265</ASTROBJ> is a G0V metal-rich
exoplanet-host star observed in the seismology field of the CoRoT
space telescope from November 2008 to March 2009. The satellite
collected 117 days of high-precision photometric data on this star,
showing that it presents solar-like oscillations. HD 52265 was also
observed in spectroscopy with the Narval spectrograph at the same
epoch. <BR /> Aims: We characterise HD 52265 using both spectroscopic
and seismic data. <BR /> Methods: The fundamental stellar parameters
of HD 52265 were derived with the semi-automatic software VWA, and
the projected rotational velocity was estimated by fitting synthetic
profiles to isolated lines in the observed spectrum. The parameters
of the observed p modes were determined with a maximum-likelihood
estimation. We performed a global fit of the oscillation spectrum,
over about ten radial orders, for degrees l = 0 to 2. We also derived
the properties of the granulation, and analysed a signature of the
rotation induced by the photospheric magnetic activity. <BR /> Results:
Precise determinations of fundamental parameters have been obtained:
T<SUB>eff</SUB> = 6100 ± 60 K, log g = 4.35 ± 0.09, [M/H] = 0.19 ±
0.05, as well as vsini=3.6<SUP>+0.3</SUP><SUB>-1.0kms</SUB>. We have
measured a mean rotation period P<SUB>rot</SUB> = 12.3 ± 0.15 days,
and find a signature of differential rotation. The frequencies of 31
modes are reported in the range 1500-2550 μHz. The large separation
exhibits a clear modulation around the mean value Dnu=98.3 ± 0.1
μHz. Mode widths vary with frequency along an S-shape with a clear
local maximum around 1800 μHz. We deduce lifetimes ranging between
0.5 and 3 days for these modes. Finally, we find a maximal bolometric
amplitude of about 3.96 ± 0.24 ppm for radial modes. <P />The CoRoT
space mission, launched on December 27th 2006, has been developed
and is operated by CNES, with the contribution of Austria, Belgium,
Brazil, ESA (RSSD and Science Programme), Germany and Spain.
---------------------------------------------------------
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: A power-spectrum autocorrelation technique to detect global
asteroseismic parameters
Authors: Verner, G. A.; Roxburgh, I. W.
2011arXiv1104.0631V Altcode:
This article describes a moving-windowed autocorrelation technique
which, when applied to an asteroseismic Fourier power spectrum, can
be used to automatically detect the frequency of maximum p-mode power,
large and small separations, mean p-mode linewidth, and constrain the
stellar inclination angle and rotational splitting. The technique is
illustrated using data from the CoRoT and Kepler space telescopes and
tested using artificial data.
---------------------------------------------------------
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: 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: 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: PLATO : PLAnetary Transits and Oscillations of Stars - The
Exoplanetary System Explorer
Authors: Catala, C.; Arentoft, T.; Fridlund, M.; Lindberg, R.;
Mas-Hesse, J. M.; Micela, G.; Pollacco, D.; Poretti, E.; Rauer, H.;
Roxburgh, I.; Stankov, A.; Udry, S.
2010ASPC..430..260C Altcode:
PLATO’s objective is to characterize exoplanets and their host stars
in the solar neighbourhood. While it builds on the heritage from
CoRoT and Kepler, the major breakthrough will come from its strong
focus on bright targets (m<SUB>V</SUB> ≤ 11). The PLATO targets
will also include a large number of very bright (m<SUB>V</SUB>
≤ 8) and nearby stars. The prime science goals of PLATO are:
(i) the detection and characterization of exoplanetary systems
of all kinds, including both the planets and their host stars,
reaching down to small, terrestrial planets in the habitable zone;
(ii) the identification of suitable targets for future, more detailed
characterization, including a spectroscopic search for bio-markers
in nearby habitable exoplanets. These ambitious goals will be reached
by ultra-high precision, long (few years), uninterrupted photometric
monitoring in the visible of very large samples of bright stars,
which can only be done from space. The resulting high quality light
curves will be used on the one hand to detect planetary transits,
as well as to measure their characteristics, and on the other hand to
provide a seismic analysis of the host stars of the detected planets,
from which precise measurements of their radii, masses, and ages
will be derived. The PLATO space-based data will be complemented by
ground-based follow-up observations, in particular very precise radial
velocity monitoring, which will be used to confirm the planetary nature
of the detected events and to measure the planet masses. The full set
of parameters of exoplanetary systems will thus be measured, including
all characteristics of the host stars and the orbits, radii, masses,
and ages of the planets, allowing us to derive planet mean densities,
and estimate their temperature and radiation environment. Finally,
the knowledge of the age of the exoplanetary systems will allow us to
put them in an evolutionary perspective.
---------------------------------------------------------
Title: The solar-like CoRoT target HD 170987: spectroscopic and
seismic observations
Authors: Mathur, S.; García, R. A.; Catala, C.; Bruntt, H.; Mosser,
B.; Appourchaux, T.; Ballot, J.; Creevey, O. L.; Gaulme, P.; Hekker,
S.; Huber, D.; Karoff, C.; Piau, L.; Régulo, C.; Roxburgh, I. W.;
Salabert, D.; Verner, G. A.; Auvergne, M.; Baglin, A.; Chaplin, W. J.;
Elsworth, Y.; Michel, E.; Samadi, R.; Sato, K.; Stello, D.
2010A&A...518A..53M Altcode: 2010arXiv1004.4891M
Context. The CoRoT mission is in its third year of observation and the
data from the second long run in the galactic centre direction are being
analysed. The solar-like oscillating stars that have been observed up
to now have given some interesting results, specially concerning the
amplitudes that are lower than predicted. We present here the results
from the analysis of the star HD 170987. <BR /> Aims: The goal of this
research work is to characterise the global parameters of HD 170987. We
look for global seismic parameters such as the mean large separation,
maximum amplitude of the modes, and surface rotation because the
signal-to-noise ratio in the observations does not allow us to measure
individual modes. We also aim to retrieve the parameters of the star
and its chemical composition. <BR /> Methods: We studied the chemical
composition of the star through ground-based observations performed
with the NARVAL spectrograph. We used several methods to calculate
the global parameters from the acoustic oscillations based on CoRoT
data. The light curve of the star has been interpolated with inpainting
algorithms to reduce the effect of data gaps. <BR /> Results: We found
the power excess related to p modes in the range [400-1200] μHz with
a mean large separation of 55.2 ± 0.8 μHz with a probability above
95 % that increases to 55.9 ± 0.2 μHz in a higher frequency range
[500-1250] μHz and a rejection level of 1%. A hint of the variation of
this quantity with frequency was also found. The rotation period of the
star is estimated to be around 4.3 days with an inclination axis of i =
50° <SUP>+20</SUP><SUB>-13</SUB>. We measured a bolometric amplitude
per radial mode in a range [2.4-2.9] ppm around 1000 μHz. Finally
we estimate the stellar mass with a grid of models, M = 1.43 ± 0.05
M_⊙, the radius, R = 1.96 ± 0.046 R_⊙, and the age ~2.4 Gyr. <P
/>The CoRoT space mission, launched on 2006 December 27, has been
developed and is operated by CNES, with the contribution of Austria,
Belgium, Brazil, ESA (RSSD and Science Programme), Germany and Spain.
---------------------------------------------------------
Title: Asteroseismology of solar and stellar models
Authors: Roxburgh, Ian W.
2010Ap&SS.328....3R Altcode: 2009Ap&SS.tmp..245R
I discuss several asteroseismology diagnostic techniques that can be
applied to the high quality data on stellar oscillations obtained,
and to be obtained in the future, from ground based and space based
experiments. In particular I discuss techniques using the representation
of oscillation frequencies in terms of inner and outer phase shifts
which can be used both for model fitting and inversion procedures
to probe the inner structure of stars, and hence to test and improve
our modelling.
---------------------------------------------------------
Title: Seismic and spectroscopic characterization of the solar-like
pulsating CoRoT target HD 49385
Authors: Deheuvels, S.; Bruntt, H.; Michel, E.; Barban, C.; Verner,
G.; Régulo, C.; Mosser, B.; Mathur, S.; Gaulme, P.; Garcia, R. A.;
Boumier, P.; Appourchaux, T.; Samadi, R.; Catala, C.; Baudin, F.;
Baglin, A.; Auvergne, M.; Roxburgh, I. W.; Pérez Hernández, F.
2010A&A...515A..87D Altcode: 2010arXiv1003.4368D
Context. The star HD 49385 is the first G-type solar-like pulsator
observed in the seismology field of the space telescope CoRoT. The
satellite collected 137 days of high-precision photometric data on
this star, confirming that it presents solar-like oscillations. HD
49385 was also observed in spectroscopy with the NARVAL spectrograph in
January 2009. <BR /> Aims: Our goal is to characterize HD 49385 using
both spectroscopic and seismic data. <BR /> Methods: The fundamental
stellar parameters of HD 49385 are derived with the semi-automatic
software VWA, and the projected rotational velocity is estimated by
fitting synthetic profiles to isolated lines in the observed spectrum. A
maximum likelihood estimation is used to determine the parameters of
the observed p modes. We perform a global fit, in which modes are fitted
simultaneously over nine radial orders, with degrees ranging from ℓ =
0 to ℓ = 3 (36 individual modes). <BR /> Results: Precise estimates of
the atmospheric parameters (T<SUB>eff</SUB>, [M/H], log g) and of the ν
sin i of HD 49385 are obtained. The seismic analysis of the star leads
to a clear identification of the modes for degrees ℓ = 0,1,2. Around
the maximum of the signal (ν ≃ 1013 μHz), some peaks are found
significant and compatible with the expected characteristics of ℓ =
3 modes. Our fit yields robust estimates of the frequencies, linewidths
and amplitudes of the modes. We find amplitudes of ~5.6 ± 0.8 ppm for
radial modes at the maximum of the signal. The lifetimes of the modes
range from one day (at high frequency) to a bit more than two days
(at low frequency). Significant peaks are found outside the identified
ridges and are fitted. They are attributed to mixed modes. <P />Based
on data obtained from the CoRoT (Convection, Rotation and planetary
Transits) space mission, developed by the French Space agency CNES
in collaboration with the Science Programs of ESA, Austria, Belgium,
Brazil, Germany and Spain.Based on data obtained using the Télescope
Bernard Lyot at Observatoire du Pic du Midi, CNRS and Université Paul
Sabatier, France.
---------------------------------------------------------
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: 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: A fresh look at the seismic spectrum of HD49933: analysis of
180 days of CoRoT photometry
Authors: Benomar, O.; Baudin, F.; Campante, T. L.; Chaplin, W. J.;
García, R. A.; Gaulme, P.; Toutain, T.; Verner, G. A.; Appourchaux,
T.; Ballot, J.; Barban, C.; Elsworth, Y.; Mathur, S.; Mosser, B.;
Régulo, C.; Roxburgh, I. W.; Auvergne, M.; Baglin, A.; Catala, C.;
Michel, E.; Samadi, R.
2009A&A...507L..13B Altcode: 2009arXiv0910.3060B
Context: Solar-like oscillations have now been observed in several
stars, thanks to ground-based spectroscopic observations and space-borne
photometry. CoRoT, which has been in orbit since December 2006, has
observed the star HD49933 twice. The oscillation spectrum of this
star has proven difficult to interpret. <BR />Aims: Thanks to a new
timeseries provided by CoRoT, we aim to provide a robust description
of the oscillations in HD49933, i.e., to identify the degrees of the
observed modes, and to measure mode frequencies, widths, amplitudes
and the average rotational splitting. <BR />Methods: Several methods
were used to model the Fourier spectrum: Maximum Likelihood Estimators
and Bayesian analysis using Markov Chain Monte-Carlo techniques. <BR
/>Results: The different methods yield consistent result, and allow us
to make a robust identification of the modes and to extract precise
mode parameters. Only the rotational splitting remains difficult to
estimate precisely, but is clearly relatively large (several μHz in
size). <P />The CoRoT space mission, launched on 2006 December 27,
was developed and is operated by the CNES, with participation of
the Science Programs of ESA, ESA's RSSD, Austria, Belgium, Brazil,
Germany and Spain. <P />Figures 5-9 and Table 2 are only available in
electronic form at http://www.aanda.org
---------------------------------------------------------
Title: The CoRoT target HD 175726: an active star with weak solar-like
oscillations
Authors: Mosser, B.; Michel, E.; Appourchaux, T.; Barban, C.; Baudin,
F.; Boumier, P.; Bruntt, H.; Catala, C.; Deheuvels, S.; García,
R. A.; Gaulme, P.; Regulo, C.; Roxburgh, I.; Samadi, R.; Verner, G.;
Auvergne, M.; Baglin, A.; Ballot, J.; Benomar, O.; Mathur, S.
2009A&A...506...33M Altcode: 2009arXiv0908.2244M
Context: The CoRoT short runs give us the opportunity to observe a large
variety of late-type stars through their solar-like oscillations. We
report observations of the star HD 175726 that lasted for 27 days
during the first short run of the mission. The time series reveals a
high-activity signal and the power spectrum presents an excess due to
solar-like oscillations with a low signal-to-noise ratio. <BR />Aims:
Our aim is to identify the most efficient tools to extract as much
information as possible from the power density spectrum. <BR />Methods:
The most productive method appears to be the autocorrelation of the
time series, calculated as the spectrum of the filtered spectrum. This
method is efficient, very rapid computationally, and will be useful for
the analysis of other targets, observed with CoRoT or with forthcoming
missions such as Kepler and Plato. <BR />Results: The mean large
separation has been measured to be 97.2±0.5 μHz, slightly below the
expected value determined from solar scaling laws. We also show strong
evidence for variation of the large separation with frequency. The
bolometric mode amplitude is only 1.7±0.25 ppm for radial modes, which
is 1.7 times less than expected. Due to the low signal-to-noise ratio,
mode identification is not possible for the available data set of HD
175726. <P />The CoRoT space mission, launched on 2006 December 27, was
developed and is operated by the CNES, with participation of the Science
Programs of ESA, ESAs RSSD, Austria, Belgium, Brazil, Germany and Spain.
---------------------------------------------------------
Title: Solar-like oscillations in HD 181420: data analysis of 156
days of CoRoT data
Authors: Barban, C.; Deheuvels, S.; Baudin, F.; Appourchaux, T.;
Auvergne, M.; Ballot, J.; Boumier, P.; Chaplin, W. J.; García,
R. A.; Gaulme, P.; Michel, E.; Mosser, B.; Régulo, C.; Roxburgh,
I. W.; Verner, G.; Baglin, A.; Catala, C.; Samadi, R.; Bruntt, H.;
Elsworth, Y.; Mathur, S.
2009A&A...506...51B Altcode:
Context: The estimate of solar-like oscillation properties, such
as their frequencies, amplitudes and lifetimes, is challenging
because of their low amplitudes and will benefit from long and
uninterrupted observing runs. The space telescope CoRoT allows us
to obtain high-performance photometric data over a long and quasi
continuous period. Among its main targets are stars for which we expect
solar-like oscillations. <BR />Aims: HD 181420, an F2 main sequence
star, has been observed by CoRoT during its first long run covering
about 156 days. With this unprecedently high-quality set of data,
our aim is to derive the p-mode parameters that can be used to probe
the stellar interior. <BR />Methods: The CoRoT data obtained on HD
181420 is analysed using a classical Fourier approach for the search
for the p mode signature. The p-mode parameters are then derived using
global fitting of the power spectrum by a Lorentzian model, as used
widely in the solar case. <BR />Results: From the p-mode frequencies,
the mean value of the large spacing is estimated to be 75 {μ Hz}. The
p-mode amplitudes are slightly less than 4 ppm with a line width of
about 8 {μ Hz} at the maximum of the p modes. The inclination angle is
estimated to be around 45 °. The large mode line-width combined with
the observed mode spacing make it difficult to identify the ℓ=2 modes
and to estimate the rotational splitting. We explore two scenarios
for the identification of the modes. <P />The CoRoT space mission,
launched on 2006 December 27, was delopped and is operated by the
CNES with participation of the Science Programs of ESA; ESA's RSSD,
Austria, Belgium, Brazil, Germany and Spain.
---------------------------------------------------------
Title: Solar-like oscillations with low amplitude in the CoRoT target
HD 181906
Authors: García, R. A.; Régulo, C.; Samadi, R.; Ballot, J.; Barban,
C.; Benomar, O.; Chaplin, W. J.; Gaulme, P.; Appourchaux, T.; Mathur,
S.; Mosser, B.; Toutain, T.; Verner, G. A.; Auvergne, M.; Baglin,
A.; Baudin, F.; Boumier, P.; Bruntt, H.; Catala, C.; Deheuvels, S.;
Elsworth, Y.; Jiménez-Reyes, S. J.; Michel, E.; Pérez Hernández,
F.; Roxburgh, I. W.; Salabert, D.
2009A&A...506...41G Altcode: 2009arXiv0907.0608G
Context: The F8 star HD 181906 (effective temperature ∼6300 K) was
observed for 156 days by the CoRoT satellite during the first long
run in the direction of the galactic centre. Analysis of the data
reveals a spectrum of solar-like acoustic oscillations. However, the
faintness of the target (m<SUB>v</SUB> = 7.65) means the signal-to-noise
(S/N) in the acoustic modes is quite low, and this low S/N leads to
complications in the analysis. <BR />Aims: We extract global variables
of the star, as well as key parameters of the p modes observed in the
power spectrum of the lightcurve. <BR />Methods: The power spectrum
of the lightcurve, a wavelet transform and spot fitting were used
to obtain the average rotation rate of the star and its inclination
angle. Then, the autocorrelation of the power spectrum and the power
spectrum of the power spectrum were used to properly determine the
large separation. Finally, estimations of the mode parameters were
done by maximizing the likelihood of a global fit, where several modes
were fit simultaneously. <BR />Results: We have been able to infer the
mean surface rotation rate of the star (~4 μHz) with indications of
the presence of surface differential rotation, the large separation
of the p modes (~87 μHz), hence also the “ridges” corresponding
to overtones of the acoustic modes. <P />CoRoT (Convection, Rotation
and planetary Transits) is a minisatellite developed by the French
Space agency CNES in collaboration with the Science Programmes of ESA,
Austria, Belgium, Brazil, Germany and Spain.
---------------------------------------------------------
Title: Narrow frequency-windowed autocorrelations as a diagnostic
of solar-like stars
Authors: Roxburgh, I. W.
2009A&A...506..435R Altcode:
Aims: This paper investigates the diagnostic potential of narrow,
frequency-windowed autocorrelation as a tool for probing the properties
of solar-like oscillating stars when the determination of individual
frequencies is impossible or is subject to large uncertainties, and
when mode identification is difficult. <BR />Methods: I use theoretical
analysis including phase-shifts, modelling, and data analysis. <BR
/>Results: Narrow-windowed autocorrelation of a time series can reveal
the variation with frequency of the large separations Δ(ν) and the
half large separations Δ<SUB>01</SUB>, Δ<SUB>10</SUB>, thus helping
with mode identification. This technique is applied to the CoRoT p-mode
oscillators HD 49933, HD 175726, HD 181420, and HD 181906. Theoretical
analysis and modelling are presented to illustrate the technique.
---------------------------------------------------------
Title: Response of a spaceborne gravitational wave antenna to solar
oscillations
Authors: Polnarev, A. G.; Roxburgh, I. W.; Baskaran, D.
2009PhRvD..79h2001P Altcode: 2009arXiv0904.1943P
We investigate the possibility of observing very small amplitude low
frequency solar oscillations with the proposed laser interferometer
space antenna (LISA). For frequencies ν below 3×10<SUP>-4</SUP>Hz the
dominant contribution is from the near zone time-dependent gravitational
quadrupole moments associated with the normal modes of oscillation. For
frequencies ν above 3×10<SUP>-4</SUP>Hz the dominant contribution is
from gravitational radiation generated by the quadrupole oscillations
which is larger than the Newtonian signal by a factor of the order
(2πrν/c)<SUP>4</SUP>, where r is the distance to the Sun, and c is
the velocity of light. The low order solar quadrupole pressure and
gravity oscillation modes have not yet been detected above the solar
background by helioseismic velocity and intensity measurements. We
show that for frequencies ν≲2×10<SUP>-4</SUP>Hz, the signal due to
solar oscillations will have a higher signal to noise ratio in a LISA
type space interferometer than in helioseismology measurements. Our
estimates of the amplitudes needed to give a detectable signal
on a LISA type space laser interferometer imply surface velocity
amplitudes on the sun of the order of 1-10mm/sec in the frequency
range 1×10<SUP>-4</SUP>-5×10<SUP>-4</SUP>Hz. If such modes exist
with frequencies and amplitudes in this range they could be detected
with a LISA type laser interferometer.
---------------------------------------------------------
Title: “Galileo Galilei” (GG) a small satellite to test the
equivalence principle of Galileo, Newton and Einstein
Authors: Nobili, Anna M.; Comandi, Gian Luca; Doravari, Suresh;
Bramanti, Donato; Kumar, Rajeev; Maccarrone, Francesco; Polacco, Erseo;
Turyshev, Slava G.; Shao, Michael; Lipa, John; Dittus, Hansjoerg;
Laemmerzhal, Claus; Peters, Achim; Mueller, Jurgen; Unnikrishnan,
C. S.; Roxburgh, Ian W.; Brillet, Alain; Marchal, Christian; Luo, Jun;
van der Ha, Jozef; Milyukov, Vadim; Iafolla, Valerio; Lucchesi, David;
Tortora, Paolo; de Bernardis, Paolo; Palmonari, Federico; Focardi,
Sergio; Zanello, Dino; Monaco, Salvatore; Mengali, Giovanni; Anselmo,
Luciano; Iorio, Lorenzo; Knezevic, Zoran
2009ExA....23..689N Altcode: 2009ExA...tmp....2N
“Galileo Galilei” (GG) is a small satellite designed to fly in low
Earth orbit with the goal of testing the Equivalence Principle—which
is at the basis of the General Theory of Relativity—to 1 part in
10<SUP>17</SUP>. If successful, it would improve current laboratory
results by 4 orders of magnitude. A confirmation would strongly
constrain theories; proof of violation is believed to lead to a
scientific revolution. The experiment design allows it to be carried
out at ambient temperature inside a small 1-axis stabilized satellite
(250 kg total mass). GG is under investigation at Phase A-2 level by
ASI (Agenzia Spaziale Italiana) at Thales Alenia Space in Torino,
while a laboratory prototype (known as GGG) is operational at INFN
laboratories in Pisa, supported by INFN (Istituto Nazionale di fisica
Nucleare) and ASI. A final study report will be published in 2009.
---------------------------------------------------------
Title: Small separations and phase shift differences of ℓ = 0,
1 p-modes
Authors: Roxburgh, I. W.
2009A&A...493..185R Altcode:
Aims: We investigate the diagnostic potential of ℓ = 0,1 p-modes
and the origin of the periodicity in their small separations. <BR
/>Methods: We used theoretical analysis, phase-shifts, modelling. and
data analysis. <BR />Results: The periodicity in the small separations
between modes of ℓ = 0, 1 is determined by the acoustic radius of the
base of the outer convective envelope. The mean variation is determined
primarily by the structure of the inner core. The separations are
related to the inner phase shifts differences δ_1-δ<SUB>0</SUB>
which we show can be determined directly from the frequencies. The
modulation period is shifted slightly by the frequency dependence of
the phase shifts and the amplitudes. We present results using data
from the BiSON, IRIS, and GOLF experiments, and a solar model, all
of which give a modulation period of ~359±5 μHz corresponding to an
acoustic radius ~1422±20 s.
---------------------------------------------------------
Title: First asteroseismic results from CoRoT
Authors: Michel, E.; Baglin, A.; Weiss, W. W.; Auvergne, M.; Catala,
C.; Aerts, C.; Appourchaux, T.; Barban, C.; Baudin, F.; Briquet, M.;
Carrier, F.; Degroote, P.; De Ridder, J.; Garcia, R. A.; Garrido,
R.; Gutiérrez-Soto, J.; Kallinger, T.; Lefevre, L.; Neiner,
C.; Poretti, E.; Samadi, R.; Sarro, L.; Alecian, G.; Andrade, L.;
Ballot, J.; Benomar, O.; Berthomieu, G.; Boumier, P.; Charpinet, S.;
de Batz, B.; Deheuvels, S.; Dupret, M. -A.; Emilio, M.; Fabregat,
J.; Facanha, W.; Floquet, M.; Frémat, Y.; Fridlund, M.; Goupil,
M. -J.; Grotsch-Noels, A.; Handler, G.; Huat, A. -L.; Hubert, A. -M.;
Janot-Pacheco, E.; Kjeldsen, H.; Lebreton, Y.; Leroy, B.; Martayan,
C.; Mathias, P.; Miglio, A.; Montalban, J.; Monteiro, M. J. P. F. G.;
Mosser, B.; Provost, J; Regulo, C.; Renan de Medeiros, J.; Ribas,
I.; Roca Cortés, T.; Roxburgh, I.; Suso, J.; Thoul, A.; Toutain, T.;
Tiphene, D.; Turck-Chieze, S.; Vauclair, S.; Vauclair, G.; Zwintz, K.
2008CoAst.156...73M Altcode:
About one year after the end of the first observational run and
six months after the first CoRoT data delivery, we comment the data
exploitation progress for different types of stars. We consider first
results to illustrate how these data of unprecedented quality shed a
new light on the field of stellar seismology.
---------------------------------------------------------
Title: CoRoT Measures Solar-Like Oscillations and Granulation in
Stars Hotter Than the Sun
Authors: Michel, Eric; Baglin, Annie; Auvergne, Michel; Catala,
Claude; Samadi, Reza; Baudin, Frédéric; Appourchaux, Thierry; Barban,
Caroline; Weiss, Werner W.; Berthomieu, Gabrielle; Boumier, Patrick;
Dupret, Marc-Antoine; Garcia, Rafael A.; Fridlund, Malcolm; Garrido,
Rafael; Goupil, Marie-Jo; Kjeldsen, Hans; Lebreton, Yveline; Mosser,
Benoît; Grotsch-Noels, Arlette; Janot-Pacheco, Eduardo; Provost,
Janine; Roxburgh, Ian W.; Thoul, Anne; Toutain, Thierry; Tiphène,
Didier; Turck-Chieze, Sylvaine; Vauclair, Sylvie D.; Vauclair,
Gérard P.; Aerts, Conny; Alecian, Georges; Ballot, Jérôme;
Charpinet, Stéphane; Hubert, Anne-Marie; Lignières, François;
Mathias, Philippe; Monteiro, Mario J. P. F. G.; Neiner, Coralie;
Poretti, Ennio; Renan de Medeiros, José; Ribas, Ignasi; Rieutord,
Michel L.; Roca Cortés, Teodoro; Zwintz, Konstanze
2008Sci...322..558M Altcode: 2008arXiv0812.1267M
Oscillations of the Sun have been used to understand its interior
structure. The extension of similar studies to more distant stars
has raised many difficulties despite the strong efforts of the
international community over the past decades. The CoRoT (Convection
Rotation and Planetary Transits) satellite, launched in December 2006,
has now measured oscillations and the stellar granulation signature
in three main sequence stars that are noticeably hotter than the
sun. The oscillation amplitudes are about 1.5 times as large as
those in the Sun; the stellar granulation is up to three times as
high. The stellar amplitudes are about 25% below the theoretic values,
providing a measurement of the nonadiabaticity of the process ruling
the oscillations in the outer layers of the stars.
---------------------------------------------------------
Title: CoRoT sounds the stars: p-mode parameters of Sun-like
oscillations on HD 49933
Authors: Appourchaux, T.; Michel, E.; Auvergne, M.; Baglin, A.;
Toutain, T.; Baudin, F.; Benomar, O.; Chaplin, W. J.; Deheuvels, S.;
Samadi, R.; Verner, G. A.; Boumier, P.; García, R. A.; Mosser, B.;
Hulot, J. -C.; Ballot, J.; Barban, C.; Elsworth, Y.; Jiménez-Reyes,
S. J.; Kjeldsen, H.; Régulo, C.; Roxburgh, I. W.
2008A&A...488..705A Altcode:
Context: The first asteroseismology results from CoRoT are presented,
on a star showing Sun-like oscillations. We have analyzed a 60 day
lightcurve of high-quality photometric data collected by CoRoT on the
F5 V star HD 49933. The data reveal a rich spectrum of overtones of
low-degree p modes. <BR />Aims: Our aim was to extract robust estimates
of the key parameters of the p modes observed in the power spectrum of
the lightcurve. <BR />Methods: Estimation of the mode parameters was
performed using maximum likelihood estimation of the power spectrum. A
global fitting strategy was adopted whereby 15 mode orders of the
mode spectrum (45 modes) were fitted simultaneously. <BR />Results:
The parameter estimates that we list include mode frequencies,
peak linewidths, mode amplitudes, and a mean rotational frequency
splitting. We find that the average large frequency (overtone) spacing
derived from the fitted mode frequencies is 85.9 ± 0.15 μHz. The
frequency of maximum amplitude of the radial modes is at 1760 μHz,
where the observed rms mode amplitude is 3.75 ± 0.23 ppm. The mean
rotational splitting of the non-radial modes appears to be in the
range ≈2.7 μHz to ≈3.4 μHz. The angle of inclination offered by
the star, as determined by fits to the amplitude ratios of the modes,
appears to be in the range ≈50 degrees to ≈62 degrees. <P />The
CoRoT space mission, launched on <P />2006 December 27, was developed
and is operated by the CNES, with <P />participation of the Science
Programs of ESA, ESA's RSSD, Austria, <P />Belgium, Brazil, Germany
and Spain.
---------------------------------------------------------
Title: The STAROX stellar evolution code
Authors: Roxburgh, Ian W.
2008Ap&SS.316...75R Altcode: 2007Ap&SS.tmp..434R
This paper describes the STAROX stellar evolution code for the
calculation of the evolution of a model of a spherical star. The
code calculates a model at time t <SUB> k </SUB>, that is the run
of pressure, density, temperature, radius, energy flux and related
variables on a mesh in mass M <SUB> i </SUB>, given the distribution
of chemical elements X <SUB> j </SUB>( i) at t <SUB> k </SUB> and the
model at the previous time step t <SUB> k-1</SUB>. It then advances
the chemical composition to the next time step t <SUB> k+1</SUB>
and calculates a new model at time t <SUB> k+1</SUB>. This process
is iterated to convergence. The model equations are solved by Newton
Raphson relaxation; the chemical equations are solved by an iterative
procedure, each element being advanced in turn, and the process
repeated to convergence. Convection is modelled by a mixing length
model and convective mixing is treated as a diffusive process; chemical
overshooting can be incorporated in parametric form. The equation of
state is taken from OPAL tables and the opacity from a blend of OPAL and
Alexander tables. Nuclear reaction rates are from NACRE but only cover
the p p chain and CNO cycle. The atmospheric layers are incorporated in
the model by applying the surface boundary condition at small optical
depth ( τ≈0.001). The mesh in mass M <SUB> i </SUB> is usually taken
as fixed except that there is a moveable mesh point at the boundary of
a convective core. Results are given for models of mass 0.9 and 5.0
M <SUB>⊙</SUB> with initial composition X=0.7, Z=0.02 evolved to a
state where the central hydrogen abundance is X <SUB> c </SUB>=0.35, and
for a model of mass 2.0 M <SUB>⊙</SUB> with initial X=0.72, Z=0.02,
evolved to X <SUB> c </SUB>=0.01 and with core overshooting. In this
latter case we compute two models one with and one without a moveable
mesh point at the boundary of the convective core to illustrate the
importance of having such a moveable mesh point for the determination
of the Brunt Väisälä frequency in the layers outside the core.
---------------------------------------------------------
Title: The OSCROX stellar oscillaton code
Authors: Roxburgh, Ian W.
2008Ap&SS.316..141R Altcode: 2007Ap&SS.tmp..342R
This paper describes the OSCROX stellar oscillation code for
the calculation of the adiabatic oscillations of low degree ℓ
of a spherical star. There are two principal versions: one in
Lagrangian variables (oscroxL), the second in Eulerian variables
(oscroxE). The Lagrangian code does not require values of the Brunt
Väisälä frequency or equivalently the density gradient. For ℓ=1
the oscillation equations have both an exact integral and an exact
partial wave solution, and codes oscroxL1 and oscroxE1 incorporate
these exact solutions. The difference in the frequencies obtained
with the various codes gives some estimate of the uncertainty in
the results due both to limited accuracy of hydrostatic support of
the stellar model, and the limited accuracy of the integration of the
oscillation equations. We compare the results of the different methods
by calculating the frequencies in the range 20 2500 μHz of a model of
a 1.5 M<SUB>⊙</SUB> main-sequence star (ModelJC) kindly provided by
J. Christensen-Dalsgaard for the purposes of cross comparison of codes,
a modified version of this model (ModelJCA) with improved hydrostatic
support, and of a highly accurate n=3 polytropic model of a star with
the same mass and radius. For the polytropic model the frequencies
as calculated by all codes agree to within 0.001 μHz, whereas for
the 1.5 M<SUB>⊙</SUB> main sequence model the frequency differences
reach a maximum of 0.04 μHz, due primarily to the limited accuracy
of hydrostatic support in the model; this is reduced to 0.01 μHz
for ModelJCA.
---------------------------------------------------------
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: Sir Hermann Bondi KCB
Authors: Roxburgh, Ian W.
2007BMFRS..53...45R Altcode:
Hermann Bondi was an Applied Mathematician of distinction who will be
remembered by fellow scientists for his outstanding contributions to
astronomy, cosmology and General Relativity, and particularly for his
pioneering contributions to our understanding of gravitational waves,
his foundational work on accretion, and as co-creator with Tommy Gold
and Fred Hoyle of the steady state theory of cosmology. But Hermann
had an equally important second career in scientific administration:
advising the UK Government on the Thames Barrier, as Director General
of the European Space Research Organisation (ESRO; now the European
Space Agency (ESA)), as Chief Scientific Advisor to the UK Government
on Defence and then on Energy, as Chairman of the Natural Environmental
Research Council (NERC), and finally as Master of Churchill College,
Cambridge. He was knighted in 1973. He continued his research on
gravitational radiation throughout his administrative career and
published his 16th paper in the series on gravitational waves in
2004. Hermann will be remembered not only for his contributions to
science and administration, but for his outstanding communication
skills and as a charismatic, warm, and stimulating person.
---------------------------------------------------------
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: Acoustic wave reflection by stellar cores: can it be seen in
the autocorrelation function of p-mode measurements?
Authors: Roxburgh, I. W.; Vorontsov, S. V.
2007MNRAS.379..801R Altcode: 2007MNRAS.tmp..557R
The rapid variation of density with depth in a stellar core can
distort acoustic wave propagation in stellar interiors, producing a
reflected wave. The reflectivity can come from a rapid density change
at the boundary of a convective core, or from the steep gradients
established in a radiative core during chemical evolution. We analyse
this wave reflection within the framework of wave scattering theory,
and address the question of the detectability of the reflected wave
in the autocorrelation function of stellar p-mode measurements.
---------------------------------------------------------
Title: The PLATO mission concept
Authors: Roxburgh, Ian; Catala, Claude; PLATO Consortium
2007CoAst.150..357R Altcode:
PLATO is a project for a future space mission that is intended to be
submitted in response to the upcoming ESA "Cosmic Vision" announcement
of opportunity. The science goal of PLATO is to provide a solid
observational basis to understand the formation and evolution of stars
and their planetary systems. This goal will be achieved by determining
statistically the distribution of sizes and orbits of exoplanets,
down to sub-earth sized planets and up to orbits at several AU, and
the properties of their parent stars through asteroseismology. The
observational concept of PLATO is based on ultra-high precision
photometry from space. The strategy is to identify a sample of more
than 100 000 bright stars, and to perform on all of them a long-term
high precision monitoring in white-light visible photometry. This
monitoring will be used on one hand to search for and characterize
planetary transits in front of these stars, and on the other hand to
detect and analyse oscillations of the same stars and thus probe their
internal structure and dynamics. The requirements for such a mission
are challenging: a very wide field-of-view, near 900 square degrees,
as well as a large effective collecting area, of the order of 1 m^2,
are necessary to monitor simultaneously a sufficiently large sample of
bright stars, with a sufficient photometric precision. The duration of
the monitoring must be of at least 5 years. We present an example of
instrumental concept compliant with these requirements. It involves
a large number of small pupil optics, each one illuminating its own
large format focal plane. Although challenging, this concept builds
on heritage from previous missions and previous studies, and presents
a low technological risk. Detailed industrial studies of the proposed
mission are currently being undertaken by Astrium and by Alcatel/Alenia,
and the final form of the mission concept to be submitted to ESA will
doubtless draw heavily on these studies. Due to secrecy agreements
with these companies we are not permitted, at this time, to discuss
the current stage of their studies.
---------------------------------------------------------
Title: Convection in Astrophysics (IAU S239)
Authors: Kupka, Friedrich; Roxburgh, Ian; Chan, Kwing Lam
2007IAUS..239.....K Altcode:
Preface; Session A. Modelling convection and radiative transfer; Session
B. Observational probes of convection; Session C. Convection in planets
and brown dwarfs; Session D. Stellar evolution, nucleosynthesis and
convective mixing; Session E. Oscillations, mass loss and convection;
Session F. Convection and rotation; Session G. MHD convection and
dynamos.
---------------------------------------------------------
Title: Reynolds stress models of convection in convective cores
Authors: Roxburgh, Ian W.; Kupka, Friedrich
2007IAUS..239...77R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Mixing length model of convection in stellar cores
Authors: Roxburgh, Ian W.; Kupka, Friedrich
2007IAUS..239...98R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Round table discussion of session F: convection and rotation
Authors: Roxburgh, Ian W.
2007IAUS..239..443R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Evaluation of the Scientific Performances for the Seismology
Programme
Authors: Appourchaux, T.; Berthomieu, G.; Michel, E.; Ballot, J.;
Barban, C.; Baudin, F.; Boumier, P.; De Ridder, J.; Floquet, M.;
Garcia, R. A.; Garrido, R.; Goupil, M. -J.; Lambert, P.; Lochard,
J.; Mazumdar, A.; Neiner, C.; Poretti, E.; Provost, J.; Roxburgh,
I.; Samadi, R.; Toutain, T.
2006ESASP1306..429A Altcode:
The Data Analysis Team of the Seismology Working Group of COROT
performed several hare-and-hound exercises. These exercises aimed at
putting the team in a situation as if they would analyze data coming
out of the COROT spacecraft. In total the team performed five different
exercises simulating solar-like stars (HH#1, HH#2, HH#3), classical
pulsators (HH#5), validating seismic calibration of stellar model (HH#2,
HH#3) and pushing the limit of detection (HH#4). This paper tries both
to serve as a summary and as a portal to other publications of the DAT.
---------------------------------------------------------
Title: Data Analysis Tools for the Seismology Programme
Authors: Appourchaux, T.; Berthomieu, G.; Michel, E.; Aerts, C.;
Ballot, J.; Barban, C.; Baudin, F.; Boumier, P.; De Ridder, J.;
Floquet, M.; Garcia, R. A.; Garrido, R.; Goupil, M. -J.; Lambert,
P.; Lochard, J.; Neiner, C.; Poretti, E.; Provost, J.; Roxburgh, I.;
Samadi, R.; Toutain, T.
2006ESASP1306..377A Altcode:
Tools developed by helioseismologists and by classical-pulsator
astronomers have been used in the hare-and-hound exercises for having
a several different ways of deriving the oscillation mode parameters
such as frequency or amplitude. These tools are used for deriving what
we call recipes that will allow us to obtain the mode parameters from
light curves either for solar-like stars or for classical pulsators. The
recipes are used for tagging the mode parameters as being those of
COROT. They will be used as reference or yardstick for other fitting
strategies. We will also address the issue of mode detection. Additional
tools such as time-frequency analysis will be presented.
---------------------------------------------------------
Title: The Quest for a European Space Mission in Stellar Seismology
and Planet Finding
Authors: Roxburgh, Ian W.
2006ESASP1306..521R Altcode:
The idea of a space mission for stellar activity and seismology was
conceived in France 1981-2 and underwent a series of developments
leading to the EVRIS experiment as a passenger experiment on
Mars96. Modified versions of EVRIS were proposed for other missions
including SOHO, and it was eventually launched on Mars96 and immediately
lost when Mars96 failed. In parallel more ambitious and larger missions
were proposed to ESA including PRISMA, STARS and Eddington. CoRoT was
originally conceived as a follow up mission to EVRIS but has matured
into the present CNES/International project that is the subject of this
volume. Initially these missions were devoted to stellar seismology and
activity, but were expanded to incorporate searching for planets. The
Eddington mission was initially selected by ESA in 2000 with reserve
status, then fully approved in 2002, but withdrawn from the ESA
programme in 2004, as part of the programme reduction needed to solve
the financial problems of ESA's Science Programme. The small Danish
seismology mission MONS was approved in 2002 but also subsequently
cancelled, whereas the Canadian microsatellite mission MOST was proposed
in 1997, successfully launched in 2003 and is currently collecting data.
---------------------------------------------------------
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 Seismology Programme of CoRoT
Authors: Michel, E.; Baglin, A.; Auvergne, M.; Catala, C.; Aerts,
C.; Alecian, G.; Amado, P.; Appourchaux, T.; Ausseloos, M.; Ballot,
J.; Barban, C.; Baudin, F.; Berthomieu, G.; Boumier, P.; Bohm, T.;
Briquet, M.; Charpinet, S.; Cunha, M. S.; De Cat, P.; Dupret, M. A.;
Fabregat, J.; Floquet, M.; Fremat, Y.; Garrido, R.; Garcia, R. A.;
Goupil, M. -J.; Handler, G.; Hubert, A. -M.; Janot-Pacheco, E.;
Lambert, P.; Lebreton, Y.; Lignieres, F.; Lochard, J.; Martin-Ruiz,
S.; Mathias, P.; Mazumdar, A.; Mittermayer, P.; Montalban, J.;
Monteiro, M. J. P. F. G.; Morel, P.; Mosser, B.; Moya, A.; Neiner,
C.; Nghiem, P.; Noels, A.; Oehlinger, J.; Poretti, E.; Provost, J.;
Renan de Medeiros, J.; De Ridder, J.; Rieutord, M.; Roca-Cortes, T.;
Roxburgh, I.; Samadi, R.; Scuflaire, R.; Suarez, J. C.; Theado, S.;
Thoul, A.; Toutain, T.; Turck-Chieze, S.; Uytterhoeven, K.; Vauclair,
G.; Vauclair, S.; Weiss, W. W.; Zwintz, K.
2006ESASP1306...39M Altcode: 2008arXiv0811.1080M
We introduce the main lines and specificities of the CoRoT Seismology
Core Programme. The development and consolidation of this programme has
been made in the framework of the CoRoT Seismology Working Group. With a
few illustrative examples, we show how CoRoT data will help to address
various problems associated with present open questions of stellar
structure and evolution.
---------------------------------------------------------
Title: The European Space Agency's Science Program and CoRoT
Authors: Fridlund, M.; Roxburgh, I.; Favata, F.; Volonté, S.
2006ESASP1306..135F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Seismic Determination of Stellar Parameters
Authors: Provost, J.; Berthomieu, G.; Gonczi, G.; Morel, P.; Toutain,
T.; Barban, C.; Goupil, M. -J.; Lebreton, Y.; Michel, E.; Roxburgh, I.
2006ESASP1306..443P Altcode:
In the context of the preparation for CoRoT, we have studied some
theoretical properties of the frequencies of solar-like stars. In
order to prepare for the interpretation of future data, we have defined
between Meudon (LESIA) and Nice (Cassini) an hare and hounds exercise
as follows: from a set of frequencies provided by each group and given
to the other group, find the characteristics of the corresponding
stellar model. Here are reported preliminary results obtained by the
Nice group. A discussion on the numerical accuracy of theoretical
frequencies is also given.
---------------------------------------------------------
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: 2-dimensional models of rapidly rotating stars. II. Hydrostatic
and acoustic models with Ω=Ω(r,θ)
Authors: Roxburgh, I. W.
2006A&A...454..883R Altcode:
Aims.We show how to construct 2-dimensional models of rapidly rotating
stars in hydrostatic equilibrium for any Ω(r,θ), given the density
ρ_m(r) along any one angle θ_m. If the hydrogen abundance X_m(r)
is given on θ<SUB>m</SUB> then the adiabatic exponent Γ_1(r,θ)
can by determined, yielding a self consistent acoustic model that can
be used to investigate the oscillation properties of rapidly rotating
stars.<BR /> Methods: .The system of equations governing the hydrostatic
structure is solved by iteration using the method of characteristics and
spectral expansion, subject to the condition that ρ(r,θ)=ρ_m(r) on
θ=θ_m. Γ_1(r,θ) is calculated from the equation of state under the
assumption that X(r,θ_m)=X_m(r) and is constant on surfaces of constant
entropy. Alternatively Γ<SUB>1</SUB> can be approximated by taking X
constant in the equation of state and equal to the surface value.<BR />
Results: .Results are presented for an evolved main sequence star of
2~M_⊙ with the angular velocity a function only of radius Ω=Ω(r),
evolved to a central hydrogen abundance of X_c=0.35. The model is
first calculated using a spherically averaged stellar evolution code,
where the averaged centrifugal force 2Ω<SUP>2</SUP> r/3 is added
to gravity. The resulting ρ_m(r), X_m(r) are then used as input to
determine the 2-dimensional model.<BR /> Conclusions: .The procedure
described here gives self consistent hydrostatic and acoustic models
of rapidly rotating stars for any Ω(r,θ).
---------------------------------------------------------
Title: PLATO: PLAnetary Transits and Oscillations of stars
Authors: Roxburgh, I. W.; Catala, C.
2006IAUJD..17E..32R Altcode:
PLATO is a project for a future space mission that is intended
to be presented in response to the upcoming ESA "Cosmic Vision"
announcement of opportunity. The science goal of PLATO is to provide
a solid observational basis to understand the formation and evolution
of stars and their planetary systems. This goal will be achieved
by determining statistically the distribution of sizes and orbits of
exoplanets, down to sub-earth sized planets and up to orbits at several
AU. The observational concept of PLATO is based on ultra-high precision
photometry from space. The strategy is to identify a sample of more
than 100,000 bright stars, and to perform on all of them a long-term
high precision monitoring in white-light visible photometry. This
monitoring will be used on one hand to search for and characterize
planetary transits in front of these stars, and on the other hand to
detect and analyse oscillations of the same stars and thus probe their
internal structure and dynamics. The requirements for such a mission
are challenging: a very wide field-of-view, near 900 square degrees, as
well as a large effective collecting area, of the order of one square
metre, are necessary to monitor simultaneously a sufficiently large
sample of bright stars, with a sufficient photometric precision. The
duration of the monitoring must be of at least five years. We present
an example instrumental concept compliant with these requirements. It
involves a large number of small pupil optics, each one illuminating
its own large format focal plane. Although challenging, this concept
builds on heritage from previous missions and previous studies, and
presents a low technological risk.
---------------------------------------------------------
Title: The CoRoT mission: Asteroseismology and Planet Finding
Authors: Roxburgh, I. W.; Baglin, A.
2006IAUJD..17E..31R Altcode:
The CoRoT mission, scheduled for launch in October 2006, has two
core science goals: the detection and characterisation of planets,
both earth like and gaseous giants, around other stars; and the
detection of oscillations of selected target stars and the use of such
oscillations to probe the interior structure and dynamics of stars,
and so to test and develop our understanding of stellar structure and
evolution. CoRoT has been developed within the framework of the French
CNES small- satellite programme, with contributions from Austria,
Belgium, Brazil, ESA, ESTEC, Germany, and Spain. It will perform
relatively broad- band photometry in visible light with a 28 cm off-
axis telescope and four CCDs, two of which are devoted to the planet
search programme and two to the seismology programme. It will have
several ( five or six ) long observing runs (150 days) on several
target fields; in the seismology programme it will simultaneously
observe ten target stars per field (with m[v][ ] < 9), chosen to
give wide coverage of the H-R diagram. In addition to the long runs
there will be two initial runs of 60 and 30 days duration, and five
or six short runs of 20 days. There is a Guest Investigator programme
in which the data from the planet search fields (about 4000 stars)
can be used for seismology on fainter stars, and for other science
goals than planet finding, and a few short runs which can be for other
science than the core planet finding and seismology.
---------------------------------------------------------
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: The autocorrelation function of stellar p-mode measurements
and its diagnostic properties
Authors: Roxburgh, I. W.; Vorontsov, S. V.
2006MNRAS.369.1491R Altcode: 2006MNRAS.tmp..549R
The basic properties of acoustic wave propagation in stellar interiors
can be analysed from the autocorrelation function (ACF) of intensity
(or velocity) observations without measuring the resonant p-mode
frequencies. We show how the strength of acoustic wave refraction in
the stellar core, or forward acoustic amplitude, can be measured from a
modulation in the ACF. This is the basic physical quantity which governs
the so-called `small frequency separations', and its measurement from
the ACF can be used for determining the small frequency separations
when the data is of insufficient quality for a reliable identification
of the stellar p-mode frequencies.
---------------------------------------------------------
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: 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: The ratio of small to large separations of stellar p-modes
Authors: Roxburgh, I. W.
2005A&A...434..665R Altcode:
In previous papers we showed that the ratios of the small to
large separations of acoustic oscillations in solar-like stars are
approximately independent of the structure of the outer layers, and
are therefore diagnostics of the interior structure alone. Here we
present similar results for a range stellar models of mass 0.8, 1.0,
1.2, 1.5, 2, 10~ M_⊙, all of which show this same property.
---------------------------------------------------------
Title: 2-dimensional models of rapidly rotating stars I. Uniformly
rotating zero age main sequence stars
Authors: Roxburgh, I. W.
2004A&A...428..171R Altcode:
We present results for 2-dimensional models of rapidly rotating main
sequence stars for the case where the angular velocity Ω is constant
throughout the star. The algorithm used solves for the structure on
equipotential surfaces and iteratively updates the total potential,
solving Poisson's equation by Legendre polynomial decomposition;
the algorithm can readily be extended to include rotation constant on
cylinders. We show that this only requires a small number of Legendre
polynomials to accurately represent the solution. We present results
for models of homogeneous zero age main sequence stars of mass 1, 2,
5, 10 M<SUB>⊙</SUB> with a range of angular velocities up to break
up. The models have a composition X=0.70, Z=0.02 and were computed
using the OPAL equation of state and OPAL/Alexander opacities, and a
mixing length model of convection modified to include the effect of
rotation. The models all show a decrease in luminosity L and polar
radius R<SUB>p</SUB> with increasing angular velocity, the magnitude
of the decrease varying with mass but of the order of a few percent for
rapid rotation, and an increase in equatorial radius R<SUB>e</SUB>. Due
to the contribution of the gravitational multipole moments the parameter
Ω<SUP>2</SUP> R<SUB>e</SUB><SUP>3</SUP>/GM can exceed unity in very
rapidly rotating stars and R<SUB>e</SUB>/R<SUB>p</SUB> can exceed 1.5.
---------------------------------------------------------
Title: The Eddington Mission
Authors: Roxburgh, I.; Favata, F.
2004IAUS..215..323R Altcode:
No abstract at ADS
---------------------------------------------------------
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: Small frequency separations as seen in the autocorrelation
function of the whole-disk measurements
Authors: Kholikov, Sh. S.; Roxburgh, I. W.; Vorontsov, S. V.
2004ESASP.538..331K Altcode: 2004sshp.conf..331K
We address the origin of the apparent modulation in the amplitudes of
the even and odd peaks in the autocorrelation function of whole-disk
measurements, and show that this modulation is directly related to the
small frequency separations of the low-degree p-modes. This modulation
can be used for estimating the small separations when the data quality
is insufficient for reliable identification of oscillation frequencies
in noisy power spectra.
---------------------------------------------------------
Title: Eddington and the internal constitution of the stars
Authors: Roxburgh, I. W.
2004ESASP.538...23R Altcode: 2004sshp.conf...23R
Eddington will provide sets of frequencies of multimode oscillations for
a very large number of stars of different masses, ages, compositions
and angular velocities. This will enable us to infer their interior
structure and dynamics, and hence to test our current understanding of
stellar structure and to develop an empirically based theory of stellar
evolution. Here I discuss some of the techniques available for inferring
the structure of stars from a given set of frequencies. In particular,
I demonstrate that, at least in solar type stars, the ratio of small
to large separations subtracts off the contribution of the surface
layers yielding a diagnostic of the stellar interior alone.
---------------------------------------------------------
Title: Science requirements and their translation into instrumental
design
Authors: Catala, C.; Aricha, A.; Boulade, O.; Diaz, E.; Epstein,
G.; Favata, F.; Horne, K.; Kjeldsen, H.; Lumb, D.; Mas-Hesse, M.;
Roxburgh, I. W.
2004ESASP.538...39C Altcode: 2004sshp.conf...39C
The detailed science requirement of Eddington are reviewed, as derived
from the major scientific objectives of the mission. An analysis of
these requirements in terms of basic mission specifications is then
given, in particular concerning the focal plane assembly and the CCD
operation mode.
---------------------------------------------------------
Title: The scattering of acoustic waves by a stellar core as seen
in the small frequency separations
Authors: Roxburgh, I. W.; Vorontsov, S. V.
2004ESASP.538..403R Altcode: 2004sshp.conf..403R
The propagation of acoustic waves in the interior of relatively young
stars is nearly classical and can be accurately described by ray-tracing
techniques. At later stages of evolution, the development of a steep
density gradient in the central core leads to wave diffraction and
partial wave scattering. Scattering is also produced by a small
convective core with a rapid density variation at the boundary. We
discuss the signatures of this scattering in the small frequency
separations of low-degree p-modes.
---------------------------------------------------------
Title: The ratio of small to large separations of acoustic
oscillations as a diagnostic of the interior of solar-like stars
Authors: Roxburgh, I. W.; Vorontsov, S. V.
2003A&A...411..215R Altcode:
By considering stellar models with the same interior structure but
different outer layers we demonstrate that the ratio of the small
to large separations of acoustic oscillations in solar-like stars
is essentially independent of the structure of the outer layers,
and is determined solely by the interior structure. Defining the
scaled Eulerian pressure perturbation psi<SUB>l</SUB> (omega ,t)
= r p' /(rho c)<SUP>1/2</SUP> we define the internal phase shift
delta<SUB>l</SUB> (omega ,t) through the relation omega psi /(dpsi
/dt)=tan (omega t -pil /2 + delta<SUB>l</SUB> ). The delta<SUB>l</SUB>
are almost independent of acoustic radius t=int dr/c outside the
stellar core and can be determined as a continuous functions of omega
from partial wave solutions for the interior - that is solutions
of the oscillation equations for any omega that satisfy the Laplace
boundary condition at a sufficiently large acoustic radius t<SUB>f</SUB>
outside the stellar core. If the omega are eigenfrequencies then they
satisfy the Eigenfrequency Equation omega T=(n+l/2) pi +alpha (omega
)-delta<SUB>l</SUB> (omega ) where alpha (omega ) is the l independent
surface phase shift (Roxburgh & Vorontsov 2000). Using this result
we show that the ratio of small to large separations is determined to
high accuracy solely by the internal phase shifts delta<SUB>l</SUB>
(omega ) and hence by the interior structure alone. The error in this
result is estimated and shown to be smaller than that associated with
the errors in the determination of the frequencies (~0.1-0.3 mu Hz)
from the upcoming space missions MOST, COROT and Eddington.
---------------------------------------------------------
Title: The cronos hydrogen maser clock redshift experiment on
Radioastron
Authors: Busca, G.; Bernier, L. G.; Schweda, H.; Kardashev, N.;
Andreianov, V.; Roxburgh, I. W.; Polnarev, S.
2003AdSpR..32.1421B Altcode:
The Radioastron satellite, having a highly elliptical orbit with a
period of 28 hours and a mission duration of more than 3 years, offers
the interesting possibility of a redshift experiment. The Space Hydrogen
Maser, recently introduced as a new instrument on the satellite in
order to be used as local oscillator for the Space VLBI, can in fact be
tracked in frequency from the ground stations, implementing only minor
modifications in the originally planned frequency transfer system. The
modified system allows also the measurements of the geometric and
ionospheric Doppler shifts. An analysis of the best strategy for
achieving the highest measurement precision is presented. The analysis
takes into account the maser frequency stability, its environmental
sensitivities, and the other known sources of noise. The error budget
of the experiment is established.
---------------------------------------------------------
Title: The Eddington Mission
Authors: Roxburgh, I.
2003Ap&SS.285..363R Altcode:
The Eddington mission was given full approval by the European Space
Agency on the 23rd May 2002, with launch scheduled for 2007/8. Its
science objectives are stellar evolution and asteroseismology, and
planet finding. In its current design it consists of 4 × 60 cm folded
Schmidt telescopes, each with 6<SUP>o</SUP> × 6<SUP>o</SUP> field
of view and its own CCD array camera. Eddington will spend 2 years
primarily devoted to asteroseismology with 1 3 months on different
target fields monitoring up to 50,000 stars per field, and 3 years
continuously on a single field monitoring upwards of 100,000 stars
for planet searching. The asteroseismic goal is to be able to detect
oscillations frequencies of stars with a precision 0.1 0.3 μHz, to
probe their interior structure and the study the physical processes
that govern their evolution.
---------------------------------------------------------
Title: Numerical 3D constraints on convective eddy time-correlations:
Consequences for stochastic excitation of solar p modes
Authors: Samadi, R.; Nordlund, Å.; Stein, R. F.; Goupil, M. J.;
Roxburgh, I.
2003A&A...404.1129S Altcode: 2003astro.ph..4457S
A 3D simulation of the upper part of the solar convective zone is used
to obtain information on the frequency component, chi<SUB>k</SUB>
, of the correlation product of the turbulent velocity field. This
component plays an important role in the stochastic excitation of
acoustic oscillations. A time analysis of the solar simulation shows
that a Gaussian function does not correctly reproduce the nu -dependency
of chi<SUB>k</SUB> inferred from the 3D simuation in the frequency range
where the acoustic energy injected into the solar p modes is important
(nu =~ 2 - 4 mHz). The nu -dependency of chi<SUB>k</SUB> is fitted
with different analytical functions which can then conveniently be
used to compute the acoustic energy supply rate P injected into the
solar radial oscillations. With constraints from a 3D simulation,
adjustment of free parameters to solar data is no longer necessary
and is not performed here. The result is compared with solar seismic
data. Computed values of P obtained with the analytical function
which fits best chi<SUB>k</SUB> are found ~ 2.7 times larger than
those obtained with the Gaussian model and reproduce better the solar
seismic observations. This non-Gaussian description also leads to
a Reynolds stress contribution of the same order as the one arising
from the advection of the turbulent fluctuations of entropy by the
turbulent motions. Some discrepancy between observed and computed
P values still exist at high frequency and possible causes for this
discrepancy are discussed.
---------------------------------------------------------
Title: Numerical constraints on the model of stochastic excitation
of solar-type oscillations
Authors: Samadi, R.; Nordlund, Å.; Stein, R. F.; Goupil, M. J.;
Roxburgh, I.
2003A&A...403..303S Altcode: 2003astro.ph..3198S
Analyses of a 3D simulation of the upper layers of a solar convective
envelope provide constraints on the physical quantities which enter
the theoretical formulation of a stochastic excitation model of solar
p modes, for instance the convective velocities and the turbulent
kinetic energy spectrum. These constraints are then used to compute
the acoustic excitation rate for solar p modes, P. The resulting
values are found ~ 5 times larger than the values resulting from a
computation in which convective velocities and entropy fluctuations are
obtained with a 1D solar envelope model built with the time-dependent,
nonlocal Gough (\cite{Gough77}) extension of the mixing length
formulation for convection (GMLT). This difference is mainly due to
the assumed mean anisotropy properties of the velocity field in the
excitation region. The 3D simulation suggests much larger horizontal
velocities compared to vertical ones than in the 1D GMLT solar
model. The values of P obtained with the 3D simulation constraints
however are still too small compared with the values inferred from
solar observations. Improvements in the description of the turbulent
kinetic energy spectrum and its depth dependence yield further increased
theoretical values of P which bring them closer to the observations. It
is also found that the source of excitation arising from the advection
of the turbulent fluctuations of entropy by the turbulent movements
contributes ~ 65-75 % to the excitation and therefore remains dominant
over the Reynolds stress contribution. The derived theoretical values
of P obtained with the 3D simulation constraints remain smaller by a
factor ~ 3 compared with the solar observations. This shows that the
stochastic excitation model still needs to be improved.
---------------------------------------------------------
Title: The Eddington Mission
Authors: Roxburgh, Ian; Favata, Fabio
2003Ap&SS.284...17R Altcode:
The Eddington mission was given full approval by the European Space
Agency on the 23rd May 2002, as part of the new `Cosmic Vision' Science
programme, with launch scheduled for 2007/8. Its twin science objectives
are asteroseismology and planet finding. In its current design it
consists of 4 × 60 cm folded Schmidt telescopes, each with 6° × 6°
field of view and its own CCD array camera. The current observing plan
is to spend 2 years primarily devoted to asteroseismology with 1-3
months on different target fields monitoring up to 50,000 stars per
field, and 3 years continuously on a single target field monitoring
upwards of 100,000 stars as required for planet searching. The
asteroseismic goal is to be able to detect oscillations frequencies
with a precision 0.1-0.3 μHz.
---------------------------------------------------------
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: Characterizing the Dynamic Properties of the Solar Turbulence
with 3-D Simulations: Consequences in Term of p-mode Excitation
Authors: Samadi, R.; Nordlund, Å.; Stein, R. F.; Goupil, M. -J.;
Roxburgh, I.
2003IAUS..210P..C2S Altcode: 2002astro.ph..8577S
A 3D simulation of the upper part of the solar convective zone is used
to derive constraints about the averaged and dynamic properties of
solar turbulent convection. Theses constraints are then used to compute
the acoustic energy supply rate P(nu) injected into the solar radial
oscillations according to the theoretical expression in Samadi &
Goupil (2001). The result is compared with solar seismic data. Assuming,
as it is usually done, a gaussian model for the frequency (nu)
component chi_k(nu) of the model of turbulence, it is found that the
computed P(nu) is underestimated compared with the solar seismic data
by a factor ~ 2.5. A frequency analysis of the solar simulation shows
that the gaussian model indeed does not correctly model chi_k(nu) in
the frequency range where the acoustic energy injected into the solar
p-modes is important (nu ~ 2 - 4 mHz). One must consider an additional
non-gaussian component for chi_k(nu) to reproduce its behavior. Computed
values of P obtained with this non-gaussian component reproduce better
the solar seismic observations. This non-gaussian component leads to
a Reynolds stress contribution of the same order than the one arising
from the advection of the turbulent fluctuations of entropy by the
turbulent motions.
---------------------------------------------------------
Title: The Asteroseismic Diagram for =0,1 p-modes
Authors: Mazumdar, A.; Roxburgh, I.
2003aahd.conf..477M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Diagnostics of the Internal Structure of Stars using the
Differential Response Technique
Authors: Roxburgh, Ian; Vorontsov, Sergei
2003Ap&SS.284..187R Altcode:
We address the problem of the diagnosing the deep interior structure
of stars using acoustic p-modes, and investigate the diagnostic
capabilities of two complementary approaches both based on the
differential response technique (Vorontsov, 1998): (a) direct
calibration using a grid of evolutionary stellar models, and (b)
linear and non-linear (with consecutive linearisations) inversion of
low-degree frequencies. We apply this analysis to the frequencies of a
model of an old 0.8M<SUB>solar</SUB> star, and to the solar frequencies
obtained from BiSON measurements, using a 2-D grid of reference models
of different mass and age. We explore the convergence and stability of
the asteroseismic inversion, performed with the adaptive regularisation
technique of Strakhov and Vorontsov (2001).
---------------------------------------------------------
Title: Consequences of the non gaussian character of the stochastic
excitation for solar-type oscillations
Authors: Samadi, R.; Nordlund, A.; Stein, R. F.; Goupil, M. -J.;
Roxburgh, I.
2002sf2a.conf..489S Altcode: 2002astro.ph.10028S
Stochastic excitation of stellar p-modes of low massive stars (M <
2Mo) are attribued to regular turbulent cells moving in the upper
convective zone. The current calculation of the acoustic energy supply
rate P - which ensures the p-modes excitation - is mainly based on this
simplifying picture and thus assume a crude description of the static
and dynamic properties of the turbulent medium. With the help of a 3D
simulation of the solar convective zone, we show that the gaussian model
does not sastisfactory model the dynamical behavior of the turbulent
medium in the frequency range where the acoustic energy injected into
the solar p-modes is important (frequency : 2 - 4 mHz). Instead, one
has to consider an additionnal component - which slowly decreases with
frequency - to reproduce better the dynamic of the turbulence. This
non-gaussian component is suggested arising from presence of plumes
in the solar convection region. Inclusion of it leads to a Reynolds
stress contribution of the same order than the one arising from the
advection of the turbulent fluctuations of entropy by the turbulent
movements. In the present work we investigate some consequences of this
non-gaussian component for the p-modes excitation in low massive stars
(M < 2Mo) and compare our computations of P with previous estimates.
---------------------------------------------------------
Title: Semiclassical analysis of stellar p modes
Authors: Roxburgh, I. W.; Vorontsov, S. V.
2002ESASP.485..345R Altcode: 2002sshp.conf..345R
We present a brief overview of our first studies in developing classical
and semiclassical approximations for low-degree stellar p modes, as an
alternative to the formal high-frequency asymptotic expansions used
earlier. The complete account of this work can be found in Roxburgh
and Vorontsov (2000, 2001).
---------------------------------------------------------
Title: Preface (Stellar structure and habitable planet finding)
Authors: Favata, Fabio; Roxburgh, Ian W.; Giménez, Alvaro
2002ESASP.485D...3F Altcode: 2002sshp.confD...3F
No abstract at ADS
---------------------------------------------------------
Title: The tools of asteroseismology
Authors: Roxburgh, I. W.
2002ESASP.485...75R Altcode: 2002sshp.conf...75R
One of the twin goals of the Eddington mission is to measure stellar
oscillations and to use the measured frequencies and line profiles to
further our understanding of the structure and evolution of stars. We
here cover some of the techniques that can be used to achieve this aim.
---------------------------------------------------------
Title: Inversion for the structure of a star of 1.45 M<SUB>solar</SUB>
using the internal phase shift
Authors: Roxburgh, I. W.; Vorontsov, S. V.
2002ESASP.485..341R Altcode: 2002sshp.conf..341R
We describe the results of an inversion for the internal structure of
a star of 1.45 M<SUB>solar</SUB> using the internal phase shifts. We
derive the internal phase shifts from frequencies of p-modes with l =
0,1,2,3 in the range 500 - 2000 μHz, with random errors of the order
of 0.3 μHz. To deduce the interior structure of the star we model
the star by a set of values D<SUB>i</SUB> = Γ<SUB>1</SUB>dlogρ/dlogP
at fractional mass points q<SUB>i</SUB> and search for the values of
D<SUB>i</SUB> that give the best fit to the internal phase shifts. The
internal density profile and the mass of the convective core are
satisfactorily reproduced.
---------------------------------------------------------
Title: Stellar structure and habitable planet finding
Authors: Battrick, B.; Favata, F.; Roxburgh, I. W.; Galadi, D.
2002ESASP.485.....B Altcode: 2002sshp.conf.....B
No abstract at ADS
---------------------------------------------------------
Title: Inversion for a 0.8 M<SUB>solar</SUB> star using
differential-response technique
Authors: Roxburgh, I. W.; Vorontsov, S. V.
2002ESASP.485..337R Altcode: 2002sshp.conf..337R
We describe the results of an artificial asteroseismic inversion for an
old 0.8 M<SUB>solar</SUB> star using a limited set of low-degree p-mode
frequencies. Two separate inversions were performed with artificial
p-mode data in the degree range l = 0-3, frequency range ν = 1-5
mHz, and l = 0-2, ν = 2-4 mHz. The p-mode eigenfrequencies have been
added with 0.3 μHz Gaussian noise. The stellar mass and radius were
not supposed to be known. A recent solar model was used as an initial
reference model in the iterative nonlinear inversion.
---------------------------------------------------------
Title: Probing the solar core with low-degree p modes
Authors: Roxburgh, I. W.; Vorontsov, S. V.
2002ESASP.485..349R Altcode: 2002sshp.conf..349R
We address the question of what could be learned about the solar
core structure if the seismic data were limited to low-degree modes
only. The results of three different experiments are described. The
first is the linearized structural inversion of the p-mode frequencies
of a solar model modified slightly in the energy-generating core,
using the original (unmodified) model as an initial guess. In the
second experiment, we invert the solar p-mode frequencies measured
in the 32-month subset of BiSON data (Chaplin et al. 1998), degraded
with additional 0.1 μHz random errors, using a model of 2.6 Gyr age
from the solar evolutionary sequence as an initial approximation. This
second inversion is non-linear. In the third experiment, we compare
the same set of BiSON frequencies with current reference solar model.
---------------------------------------------------------
Title: Background to the Eddington mission
Authors: Roxburgh, I. W.
2002ESASP.485...11R Altcode: 2002sshp.conf...11R
The Eddington mission to measure stellar oscillations and search for
other planets builds on a solid history of earlier proposals and studies
for space missions to study stellar seismology and stellar activity and
to search for planets. The idea of such a mission for stellar activity
and seismology was conceived in France 1981 and underwent a series
of developments leading to the EVRIS mission which was a passenger
experiment on Mars96 and was lost when Mars96 failed. Subsequent
proposals PRISMA and STARS underwent Phase A studies in ESA but were
not selected for launch. The small French mission COROT, originally
conceived as a successor to EVRIS was selected by CNES and is now
scheduled for launch in 2004. The much more ambitious Eddington mission,
devoted to stellar seismology and planet searching was selected as a
mission (albeit with a "reserve" status) in the 2000 F2/F3 selection
round in ESA. The mission is proceeding with detailed industrial and
working group studies with the aim of being ready for launch in 2007/8
should the mission be fully approved as part of the ESA programme.
---------------------------------------------------------
Title: Gravitational multipole moments of the Sun determined from
helioseismic estimates of the internal structure and rotation
Authors: Roxburgh, I. W.
2001A&A...377..688R Altcode:
We determine the gravitational multipole moments J<SUB>2n</SUB>, n=1,5,
of the sun using a model of the interior structure and of solar rotation
obtained from helioseismic inversions. The differential rotation of the
convective zone and the underlying transition zone make only a small
(~0.5%) contribution to the quadrupole moment J_2 which is found to
have a value ~2.21x 10<SUP>-7</SUP>.
---------------------------------------------------------
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: Semiclassical approximation for low-degree stellar p modes -
III. Acoustic resonances and diagnostic properties of the oscillation
frequencies
Authors: Roxburgh, I. W.; Vorontsov, S. V.
2001MNRAS.322...85R Altcode:
We extend the classical approximation for low-degree acoustic
oscillations to take account of the effects of wave resonances
associated with the partial reflection of waves at internal boundaries
in the stellar interior. We consider explicitly the effect of a rapid
density variation at the boundary of the convective core on the small
frequency separations, and the reflection of waves at the base of the
outer convective envelope, observable in the `surface phase-shift'
function. We describe a technique that allows us to infer the `surface
phase-shift' function, known to be a valuable diagnostic tool in
solar seismology, from frequency measurements limited to p modes of
low degree only.
---------------------------------------------------------
Title: Response of a Spaceborn Gravitational Wave Antenna to Solar
Oscillations
Authors: Roxburgh, I. W.; Polnarev, A. G.; Giampieri, G.; Vorontsov,
S. V.
2001astro.ph..3472R Altcode:
We investigate the possibility of observing very small amplitude low
frequency solar oscillations with the proposed laser interferometer
space antenna LISA. For frequencies below $\sim 2\times 10^{-4}$
Hz the dominant contribution is from the near zone time dependent
gravitational quadrupole moments associated with the normal modes of
oscillation. For frequencies $\nu$ above $\sim 3\times 10^{-4}$ Hz
the dominant contribution is from gravitational radiation generated
by the quadrupole oscillations which is larger than the Newtonian
signal by a factor $\sim (2 \pi r \nu/ c)^4$, where $r$ is the
distance to the Sun, and $c$ is the velocity of light. The low order
solar quadrupole pressure and gravity oscillation modes have not yet
been detected above the solar background by helioseismic velocity and
intensity measurements. Our estimates of the amplitudes needed to give
a detectable signal on a LISA type space laser interferometer imply
surface velocity amplitudes on the sun of the order of 1-10 mm/sec
in the frequency range $1 - 5~10^{-4}$Hz. Such surface velocities are
below the current sensitivity limits on helioseismic measurements. If
modes exist with frequencies and amplitudes in this range they could
be detected with a LISA type laser interferometer.
---------------------------------------------------------
Title: Non linear inversion for the sound speed in the solar interior
using BiSON and SOI/MDI p-mode frequencies
Authors: Marchenkov, K. I.; Roxburgh, I. W.; Vorontsov, S. V.; Chaplin,
W. J.; Elsworth, Y.; Isaak, G. R.; New, R.
2001ESASP.464..531M Altcode: 2001soho...10..531M
The results of the global sound-speed inversion obtained with solar
p-mode frequencies provided by the recent high-quality observational
data (BiSON, SOI/MDI) are presented and discussed. The iterative
nonlinear inversion technique used here is a generalization (for the
case of exact solution of the adiabatic oscillation equations) of the
Born quasiasymptotic approximate inversion developed by Marchenkov et
al. (2000).
---------------------------------------------------------
Title: Numerical Simulation of Penetrative Convection above a Stellar
Convection Zone (CD-ROM Directory: contribs/singh)
Authors: Singh, H. P.; Saikia, E.; Roxburgh, I. W.; Chan, K. L.;
Srivastava, M. P.
2001ASPC..223..874S Altcode: 2001csss...11..874S
No abstract at ADS
---------------------------------------------------------
Title: Semiclassical approximation for low-degree stellar p modes -
I. The classical eigenfrequency equation
Authors: Roxburgh, I. W.; Vorontsov, S. V.
2000MNRAS.317..141R Altcode:
A new eigenfrequency equation for low-degree solar-like oscillations
in stars is developed, based on the assumption of purely classical
propagation in the stellar interior of acoustic waves modified by
buoyancy and gravity. Compared with high-frequency asymptotic analysis,
the eigenfrequency equation has a new functional form, with expansion
in powers of l(l+1) instead of 1/ω. Basic observable quantities, the
`large' and `small' frequency separations, are interpreted as the
dependence on frequency and refraction angle of a classical action
integral for waves propagating close to the stellar diameter. The new
eigenfrequency equation gives a significant improvement in accuracy
over previous analyses when tested with solar p modes, suggesting
this as an alternative and more powerful tool for applications in
stellar seismology.
---------------------------------------------------------
Title: Semiclassical approximation for low-degree stellar p modes -
II. Classical ray tracing
Authors: Roxburgh, I. W.; Vorontsov, S. V.
2000MNRAS.317..151R Altcode:
Using ray-tracing techniques, we consider nearly forward refraction
in the stellar interior of acoustic waves modified by buoyancy and
gravity. Our analysis is based on a local dispersion relation developed
to second order in the high-frequency asymptotic approximation. The
phase shifts δ<SUB>l</SUB>δ<SUB>0</SUB>(ω)+l(l+1)D<SUB>δ</SUB> (ω)
of the partial waves of stellar p modes, which govern the eigenfrequency
equation in its classical limit, are developed in terms of explicit
integrals containing the radial profiles of seismic parameters in
the stellar interior. The accuracy of the resulting description of
low-degree stellar p modes is tested using an evolutionary sequence
of solar models.
---------------------------------------------------------
Title: `Galileo Galilei' (GG) small-satellite project: an alternative
to the torsion balance for testing the equivalence principle on
Earth and in space
Authors: Nobili, A. M.; Bramanti, D.; Polacco, E.; Roxburgh, I. W.;
Comandi, G.; Catastini, G.
2000CQGra..17.2347N Altcode:
`Galileo Galilei' (GG) is a proposal for a small, low-orbit satellite
devoted to testing the equivalence principle (EP) of Galileo, Newton
and Einstein. The GG report on the phase A study recently carried
out with funding from ASI (Agenzia Spaziale Italiana) concluded that
GG can test the equivalence principle to 1 part in 10<SUP>17</SUP>
at room temperature. The main novelty is to modulate the expected
differential signal of an EP violation at the spin rate of the
spacecraft (2 Hz). Compared with other experiments, the modulation
frequency is increased by more than a factor of 10<SUP>4</SUP>, thus
reducing 1/f (low-frequency) electronic and mechanical noise. The
challenge for an EP test in space is to improve over the sensitivity
of ground-based experiments (about 1 part in 10<SUP>12</SUP>) by
many orders of magnitude, so as to deeply probe a so far totally
unexplored field; doing that with more than one pair of bodies is
an unnecessary complication. For this reason GG is now proposed with
a single pair of test masses. At present the best and most reliable
laboratory-controlled tests of the equivalence principle have been
achieved by the `Eöt-Wash' group with small test cylinders arranged on
a torsion balance placed on a turntable which provides the modulation
of the signal (a 1-2 h rotation period). The torsion balance is not
a suitable instrument in space. We have designed and built the GGG
(`GG on the Ground') prototype. It is made of coaxial test cylinders
weakly coupled (via mechanical suspensions) and quickly rotating (6
Hz achieved so far); in addition, it is well suited to be flown in
space - where the driving signal is about three orders of magnitude
stronger and the absence of weight is very helpful - inside the
coaxial, co-rotating GG cylindrical spacecraft. The GGG apparatus is
now operational. Preliminary measurement data indicate that weakly
coupled, fast-spinning macroscopic rotors can be a suitable instrument
to detect small differential effects. Rotation (up to 6 Hz so far)
is stabilized by a small passive oil damper. A finer active damper,
using small capacitance sensors and actuators as in the design of
the space experiment, is in preparation. The current sensitivity
of the GGG system is of 10<SUP>-9</SUP> m s<SUP>-2</SUP>/√Hz at
about 300 s, which can be improved because horizontal seismic noise
is rejected very well; perturbing effects of terrain tilts (due to
microseismicity and tides) will be reduced by adding a passive cardanic
suspension. As for the capacitance read-out, the current sensitivity
(5 pm displacements in 1 s integration time at room temperature) is
adequate to make GGG competitive with the torsion balance. Because
of the stronger signal and weaker coupling of the test rotors in
space, this sensitivity is also adequate for GG to reach its target
accuracy (10<SUP>-17</SUP>). Information, references, research
papers and photographs of the apparatus are available on the Web
(http://tycho.dm.unipi.it/nobili).
---------------------------------------------------------
Title: Fundamental parameters of COROT seismology targets
Authors: Catala, C.; Bouret, J. -C.; Butler, J.; Garrido, R.;
Lignieres, F.; Roxburgh, I.; Lueftinger, T.; Soubiran, C.; Katz, D.;
van't Veer, C.; Ballereau, D.; Hua, T.
2000mons.proc...37C Altcode:
We have started a ground-based effort to determine the fundamental
parameters (T<SUB>eff</SUB>, log g, Fe/H, vsini, etc...) of 1,100
potential targets of the COROT central and exploratory asteroseismology
programmes. We are setting up a database of high (35,000 - 40,000)
resolution echelle spectra and Stromgren photometric data for
all of these stars. We use echelle spectrographs at OHP (France),
Sutherland (South Africa) and La Palma (Canary Islands), as well as a
semi-automatic photometric telescope near Granada (Spain). We intend
to gather all of these data, as well as the determined parameters and
characteristics, in a single database accessible by the community.
---------------------------------------------------------
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: Convective overshooting in stellar interiors
Authors: Singh, Harinder P.; Roxburgh, Ian W.; Chan, Kwing L.
2000BASI...28...81S Altcode:
The region of turbulent convective motions in stellar envelopes
provides for both energy transport and the redistribution of chemical
elements by mixing processes. Penetration or overshooting of these
convective motions into the surrounding stable layers extends the
unstable region thereby influencing the mixing and hence the structure
and evolution of stars. We review here different approaches to the
study of convective overshooting with special emphasis on numerical
simulations. Overshooting from convective cores is also discussed.
---------------------------------------------------------
Title: Non-linear inversion for the hydrostatic structure of the
solar interior
Authors: Marchenkov, Konstantin; Roxburgh, Ian; Vorontsov, Sergei
2000MNRAS.312...39M Altcode:
We present the results of a non-linear inverse analysis for the
hydrostatic, spherically symmetric component of the solar internal
structure using the observed p-mode frequencies. The iterative
non-linear inversion technique used here is based on the succesive Born
approximation description of solar p-modes developed by Roxburgh &
Vorontsov. This description can give a high resolution of regions of
rapid variation of seismic parameters with depth (e.g., the base of
the convection zone), and accounts accurately for the strong influence
of gravity perturbations on low-degree modes which penetrate deep
into the solar core. The inversion procedure is non-linear; the
eigenfrequency equation obtained from the Born approximation is
solved by iteration. The particular target of our inverse analysis
is to achieve the highest possible resolution of the region near the
base of the solar convection zone, searching for possible signatures
of penetrative convection, element diffusion and/or strong magnetic
fields. The results of the global inversion obtained with solar p-mode
frequencies provided by the recent high-quality observational data
(GONG, SOI/MDI, GOLF) are presented and discussed.
---------------------------------------------------------
Title: Examination of Scaling Relationships Involving Penetration
Distance at the Bottom of a Stellar Convective Envelope
Authors: Saikia, E.; Singh, Harinder P.; Chan, K. L.; Roxburgh, I. W.;
Srivastava, M. P.
2000ApJ...529..402S Altcode:
A number of studies in the recent past have proposed a variety of
scaling relationships among the penetration depth (Δ<SUB>d</SUB>)
at the bottom of a convective region, the vertical velocity of the
fluid (V<SUB>z</SUB>), and the input flux (F<SUB>b</SUB>). While a
relationship of the form Δ<SUB>d</SUB>~V<SUP>3/2</SUP><SUB>z</SUB> has
been proposed by Schmitt and coworkers on the basis of the equations
of motion for buoyant plumes, Zahn proposed a similar relationship
based on scaling arguments. The relationships involving Δ<SUB>d</SUB>,
V<SUB>z</SUB>, and the input flux are based on recent two-dimensional
numerical simulations by Hurlburt and coworkers. All these scalings
were recently looked into by Singh, Roxburgh, & Chan, who performed
full three-dimensional simulations of turbulent compressible convection
for a stable-unstable-stable sandwich configuration. In the present
study, we numerically solve the full set of Navier-Stokes equations
in three dimensions in order to study the behavior of convective
motions penetrating into the bottom stable layer. We take up a series
of models differing in resolution or mesh size and aspect ratio with a
view to examine, in greater detail, the scaling relationships between
the penetration distance and other flow parameters.
---------------------------------------------------------
Title: Power series solutions of the polytrope equations
Authors: Roxburgh, Ian W.; Stockman, Lynne M.
1999MNRAS.303..466R Altcode:
We derive recurrence relations for the coefficients a_k in the
power series expansion theta(xi)=∑ a_kxi^2k of the solution of the
Lane-Emden equation, and examine the convergence of these series. For
values of the polytropic index n<n_1~1.9 the series appear to
converge everywhere inside the star. For n>n_1 the series converge in
the inner part of the star but then diverge. We also derive the series
expansions for theta, xi in powers of m=q^2/3, where q=-xi^2dtheta/dxi
is the polytropic mass. These series appear to converge everywhere
within the star for all n <= 5. Finally we show that theta(xi) can
be satisfactorily approximated (~ 1 per cent) by (1-cxi^2)/(1+exi^2)^m,
and give the values of the constants determined by a Pade approximation
to the series, and by a two-parameter fit to the numerical solutions.
---------------------------------------------------------
Title: Asteroseismological Constraints on Stellar Convective Cores
Authors: Roxburgh, I. W.; Vorontsov, S. V.
1999ASPC..173..257R Altcode: 1999sstt.conf..257R
No abstract at ADS
---------------------------------------------------------
Title: Convective Penetration in Main Sequence Stars
Authors: Roxburgh, I. W.
1999ASPC..173..103R Altcode: 1999sstt.conf..103R
No abstract at ADS
---------------------------------------------------------
Title: Response of a Spaceborn Gravitational Wave Antenna to Solar
Oscillations
Authors: Polnarev, A. G.; Giampieri, G.; Roxburgh, I. W.; Vorontsov,
S.; Martchenkov, K.
1999magr.meet.1118P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: COROT: Seismology of Stars
Authors: Roxburgh, I. W.; COROT Team
1999ASPC..173..357R Altcode: 1999sstt.conf..357R
No abstract at ADS
---------------------------------------------------------
Title: A study of penetration at the bottom of a stellar convective
envelope and its scaling relationships
Authors: Singh, Harinder P.; Roxburgh, Ian W.; Chan, Kwing L.
1998A&A...340..178S Altcode:
{A number of scaling relationships have been proposed by several
authors relating the penetration depth (Delta_ {d}) at the bottom
of a convective region to the velocity of the penetrating motions
and the input flux (F_b). These may be expressed as Delta_ {d} ~
V<SUB>zo</SUB>(3/2) for the case where the radiative conductivity
varies smoothly from the unstable to the stable zone; V<SUB>zo</SUB>
being the vertical velocity at the bottom of the convection zone. When
the conductivity varies stepwise from one zone to another, it has been
suggested that Delta_ {d} ~ (V<SUB>zo</SUB>(3) /F_b) for adiabatic
penetration and Delta_ {d} ~ F<SUB>b</SUB>(1/2) for non-adiabatic
penetration. In this paper, we study the general behaviour of motions
penetrating into the stable region at the bottom of a convective
envelope by numerically solving the full set of Navier-Stokes equations
in three dimensions. We compute a series of models which allow us to
examine the scaling relationships between the penetration distance,
the input flux and the vertical velocity.}
---------------------------------------------------------
Title: Proposed noncryogenic, nondrag-free test of the equivalence
principle in space
Authors: Nobili, A. M.; Bramanti, D.; Catastini, G.; Polacco, E.;
Genta, G.; Brusa, E.; Mitrofanov, V. P.; Bernard, A.; Touboul, P.;
Cook, A. J.; Hough, J.; Roxburgh, I. W.; Polnarev, A.; Flury, W.;
Barlier, F.; Marchal, C.
1998NewA....3..175N Altcode:
Ever since Galileo scientists have known that all bodies fall with the
same acceleration regardless of their mass and composition. Known as
the Universality of Free Fall, this is the most direct experimental
evidence of the Weak Equivalence Principle, a founding pillar of
General Relativity according to which the gravitational (passive)
mass m<SUB>g</SUB> and the inertial mass m<SUB>i</SUB> are always in
the same positive ratio in all test bodies. A space experiment offers
two main advantages: a signal about a factor of a thousand bigger than
on Earth and the absence of weight. A new space mission named GALILEO
GALILEI (GG) has been proposed (Nobili et al., 1995 [J. Astronautical
Sciences, 43, 219]; GALILEO GALILEI (GG), PRE PHASE A REPORT, ASI
(Agenzia Spaziale Italiana), September 1996) aimed at testing the weak
Equivalence Principle (EP) to 1 part in 10 <SUP>17</SUP> in a rapidly
spinning (5 Hz) drag-free spacecraft at room temperature, the most
recent ground experiments having reached the level of 10 <SUP>-12</SUP>
(Adelberger et al., 1990 [PhRvD, 42, 3267]; Su et al., 1994 [PhRvD,
50, 3614]). Here we present a nondrag-free version of GG which could
reach a sensitivity of 1 part in 10 <SUP>16</SUP>. The main feature
of GG is that, similarly to the most recent ground experiments, the
expected (low frequency) signal is modulated at higher frequency by
spinning the system, in this case by rotating the test bodies (in the
shape of hollow cylinders) around their symmetry axes, the signal
being in the perpendicular plane. They are mechanically suspended
inside the spacecraft and have very low frequencies of natural
oscillation (due to the weakness of the springs that can be used
because of weightlessness) so as to allow self-centering of the axes;
vibrational noise around the spin/signal frequency is attenuated by
means of mechanical suspensions. The signal of an EP violation would
appear at the spin frequency as a relative ( differential) displacement
of the test masses perpendicularly to the spin axis, and be detected
by capacitance sensors; thermal stability across the test masses and
for the required integration time is obtained passively thanks to
both the fast spin and the cylindrical symmetry. In the nondrag-free
version the entire effect of atmospheric drag is retained, but a
very accurate balancing of the test bodies must be ensured (through
a coupled suspension) so as to reach a high level of Common Mode
Rejection and reduce the differential effects of drag below the target
sensitivity. In so doing the complexities of a drag-free spacecraft are
avoided by putting more stringent requirements on the experiment. The
spacecraft must have a high area-to-mass ratio in order to reduce the
effects of nongravitational forces; it is therefore a natural choice
to have three pairs of test masses (in three experimental chambers)
rather than one as by Nobili et al. (1995) [J. Astronautical Sciences,
43, 219] and the mission called GALILEO GALILEI [PRE PHASE A REPORT,
ASI (Agenzia Spaziale Italiana), September 1996]. The GG setup is
specifically designed for space; however, a significant EP test on the
ground is possible — because the signal is in the transverse plane
— by exploiting the horizontal component of the gravitational and
the centrifugal field of the Earth. This ground test is underway.
---------------------------------------------------------
Title: Helioseismic Constraints on Solar Structure and the Solar
Neutrino Problem
Authors: Roxburgh, Ian W.
1998Ap&SS.261...57R Altcode: 1999Ap&SS.261...57R
No abstract at ADS
---------------------------------------------------------
Title: After Dinner Poster Paper
Authors: Roxburgh, Ian W.
1998Ap&SS.261..213R Altcode: 1999Ap&SS.261..213R
No abstract at ADS
---------------------------------------------------------
Title: Numerical simulation of penetrative convection - verifying
the scaling relation between penetration distance and the vertical
velocity
Authors: Singh, H. P.; Roxburgh, I. W.; Chan, K. L.
1998ASPC..138..313S Altcode: 1998stas.conf..313S
No abstract at ADS
---------------------------------------------------------
Title: COROT: Seismology of Stars
Authors: Roxburgh, Ian W.
1998Ap&SS.261...19R Altcode: 1999Ap&SS.261...19R
No abstract at ADS
---------------------------------------------------------
Title: On the Diagnostic Properties of Low Degree Acoustic Modes
Authors: Roxburgh, Ian W.; Vorontsov, Sergei V.
1998Ap&SS.261...21R Altcode: 1999Ap&SS.261...21R
No abstract at ADS
---------------------------------------------------------
Title: Convective Overshooting and Mixing in Stellar Evolution
Authors: Roxburgh, Ian W.
1998Ap&SS.261...43R Altcode: 1999Ap&SS.261...43R
No abstract at ADS
---------------------------------------------------------
Title: Stellar Convective Cores
Authors: Roxburgh, I. W.
1998IAUS..185...73R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the formation of line profiles of solar p-modes
Authors: Roxburgh, I. W.; Vorontsov, S. V.
1998IAUS..185..229R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Convective overshooting and stellar evolution
Authors: Roxburgh, I. W.
1998ASPC..138..411R Altcode: 1998stas.conf..411R
No abstract at ADS
---------------------------------------------------------
Title: Helioseismic Constraints on the Solar Core
Authors: Roxburgh, Ian W.
1998Ap&SS.261...37R Altcode: 1999Ap&SS.261...37R
No abstract at ADS
---------------------------------------------------------
Title: Space Asteroseismology on Later-type Stars
Authors: Roxburgh, Ian W.; Thompson, Michael J.
1998Ap&SS.261...13R Altcode: 1999Ap&SS.261...13R
No abstract at ADS
---------------------------------------------------------
Title: Semiclassical Approximation of Low-Degree Stellar p Modes
Authors: Roxburgh, I. W.; Vorontsov, S. V.
1998ESASP.418..527R Altcode: 1998soho....6..527R
Semiclassical description of the adiabatic acoustic oscillations is
developed and its accuracy is addressed in different approximations. For
modes of low degree ell, the semiclassical analysis suggests an
expansion in powers of ell+1/2 in the eigenfrequency equation, as
an alternative to the standard expansion in powers of 1/ω given by
the high-frequency asymptotic analysis. New eigenfrequency equation
demonstrates far superior accuracy in matching the oscillation
frequencies, even when the applicability of the semiclassical analysis
is significantly violated locally in the core of a centrally-condenced
star. We discuss the diagnostic capabilities of this approximate
description by applying it to solar p-mode data.
---------------------------------------------------------
Title: The Effect of Solar Oscillations on Space Gravitational
Wave Experiments
Authors: Giampieri, G.; Polnarev, A.; Roxburgh, I.; Vorontsov, S.
1998Ap&SS.261...35G Altcode: 1999Ap&SS.261...35G
No abstract at ADS
---------------------------------------------------------
Title: A Parametric Study of 3-D Simulation of Penetrative Convection
Authors: Singh, Harinder P.; Roxburgh, Ian W.; Chan, Kwing L.
1998Ap&SS.261...53S Altcode: 1999Ap&SS.261...53S
No abstract at ADS
---------------------------------------------------------
Title: Line Profiles of Solar P-Modes
Authors: Roxburgh, Ian W.; Vorontsov, Sergei V.
1998Ap&SS.261...39R Altcode: 1999Ap&SS.261...39R
No abstract at ADS
---------------------------------------------------------
Title: Asymptotic description and the diagnostic properties of
low-degree stellar p-modes
Authors: Roxburgh, I. W.; Vorontsov, S. V.
1998IAUS..185..391R Altcode:
We describe a new development of the asymptotic theory of high-frequency
stellar acoustic oscillations, which focuses on low-degree modes and
which is motivated by its application in stellar seismology, when
the ammount of the observational data and the accuracy of frequency
measurements are rather limited. When developing the asymptotic
expansion of the solutions of the wave equations, we use new small
parameter (ell + 1/2) omega, with degree ell and frequency omega,
instead of a standard small parameter 1 omega. Such an alternative
choise of the small parameter leads to a simple second-order asymptotic
eigenfrequency equation which fits the exact frequencies with much
better accuracy. Fitting with observational data thus provides an
efficient separation of the diagnostic information contained in the
stellar frequencies, filtering the contribution of the stellar core
and the near-surface effects.
---------------------------------------------------------
Title: Non Linear Inversion for the Hydrostatic Structure of the
Solar Interior
Authors: Marchenkov, K. I.; Roxburgh, I. W.; Vorontsov, S. V.
1998Ap&SS.261...51M Altcode: 1999Ap&SS.261...51M
No abstract at ADS
---------------------------------------------------------
Title: Nonlinear inversion for the hydrostatic structure of the
solar interior
Authors: Marchenkov, Konstantin; Roxburgh, Ian; Vorontsov, Sergei
1998IAUS..185..117M Altcode:
We present the results of a nonlinear inverse analysis of the
hydrostatic spherically-symmetric component of the solar internal
structure using p-mode frequencies from the observational data sets
now available. The technique which we use is an iterative nonlinear
inversion technique, based on the "quasi-asymptotic" description of
solar p-modes developed by Roxburgh and Vorontsov (1996, MNRAS 278,
940). As a significant improvement of the standard asymptotic analysis,
this description incorporates Born approximation to allow a detailed
treatment of regions of rapid variation of seismic parameters with
depth (base of the convection zone) and strong influence of gravity
perturbations (low-degree modes which penetrate deep into the solar
core). The primary target of our current analysis is to achive the
highest possible resolution of the region around the base of the solar
convection zone, for searching possible signatures of penetrative
convection, element diffusion and/or strong magnetic fields.
---------------------------------------------------------
Title: Numerical simulation of penetrative convection - a parametric
study
Authors: Singh, Harinder P.; Roxburgh, Ian W.; Chan, Kwing L.
1998IAUS..185..123S Altcode:
In an earlier study (Singh, Roxburgh, & Chan, 1995, A & A 295,
703), we presented results of a series of 3D numerical experiments on
convective penetration into stable layers below some deep stellar - type
convective envelopes. A number of models were computed by systematically
varying the stability of the lower stable layer and it was observed
that the penetration distance decreased as the stability of the lower
stable layer was increased. In this paper we present the results of some
further studies wherein we have varied a number of input parameters
like the input flux and the aspect ratio. The effect of the changes
on the penetration distance below a convection zone has been analyzed.
---------------------------------------------------------
Title: Nonlinear Iterative Inversion for the Hydrostatic Structure
of the Solar Interior
Authors: Marchenkov, K. I.; Roxburgh, I. W.; Vorontsov, S. V.
1998ESASP.418..491M Altcode: 1998soho....6..491M
We present the results of a nonlinear inverse analysis of the
hydrostatic spherically-symmetric component of the solar internal
structure using the observational p-mode frequencies (GONG, SOI/MDI,
GOLF). The technique which we use is an iterative nonlinear inversion
technique, based on the asymptotic description of solar p modes
developed by Roxburgh and Vorontsov (1996). As a significant improvement
of the standard asymptotic analysis, this description incorporates
a Born approximation to allow for an accurate treatment of regions
of rapid variation of seismic parameters with depth (e.g. base of the
convection zone), and for better treatment of the influence of gravity
perturbations on low-degree modes which penetrate deep into the solar
core. The main target of our inverse analysis is to achive the highest
possible resolution in the solar interior, including the region near the
base of the solar convection zone, for searching possible signatures of
penetrative convection, element diffusion and/or strong magnetic fields.
---------------------------------------------------------
Title: Steady Convection in Deep Compressible Layers
Authors: Roxburgh, Ian W.
1998Ap&SS.261...55R Altcode: 1999Ap&SS.261...55R
No abstract at ADS
---------------------------------------------------------
Title: Convective Overshooting and Mixing
Authors: Roxburgh, I.
1997ASSL..225...23R Altcode: 1997scor.proc...23R
Convection is of major importance in both energy transport and mixing
in stars. Convective penetration, or overshooting, from unstable into
the surrounding stable layers, extends the zone of effective mixing
influencing both the thermal structure and evolution of stars. We here
consider a range of approaches that can advance our understanding
of this phenomenon: the fitting of stellar models to clusters and
binary systems, theoretical studies, numerical simulation, and the
new tools of helio- and asteroseismology. Other mixing processes that
may affect the evolution of the sun and stars are also discussed,
as is the possible effect of mixing on the solar neutrino problem.
---------------------------------------------------------
Title: Experiments on fundamental physics on the space station
Authors: Spallicci, A.; Brillet, A.; Busca, G.; Catastini, G.; Pinto,
I.; Roxburgh, I.; Salomon, C.; Soffel, M.; Veillet, C.
1997CQGra..14.2971S Altcode:
Original proposals and experiments on gravitation and fundamental
metrology on the space station are described. These experiments were
formulated in the Metrology and Gravitation Science Team, in two
ESA industrial study contracts, on microsatellites and on time and
frequency science, within the space station scenario. Although limited
by the design constraints of the space station, the experiments range
from clock-based tests on special and general relativity to, with
additional infrastructure, the equivalence principle and the detection
of gravitational waves. Supporting technology, such as damping systems
and microgravity cooled atom clocks, is also described. Finally,
the major scientific goals, the experiments, hardware and the status
are summarized. This work represents the first coordinated attempt,
at least within the European space programmes, to consider experiments
on relativity and fundamental physics without resorting to experiment
dedicated space missions. For details on specific issues a large
bibliography is referred to.
---------------------------------------------------------
Title: On the formation of spectral line profiles of solar P modes
Authors: Roxburgh, I. W.; Vorontsov, S. V.
1997MNRAS.292L..33R Altcode:
We address the problem of the opposite asymmetry of low-frequency p-mode
line profiles observed in intensity and velocity measurements. We
use a simple model to illustrate that this feature can be explained
by including a contribution from the stochastic excitation velocity
field to the non-resonant background in the Doppler measurements.
---------------------------------------------------------
Title: Numerical simulation of penetrative convection
Authors: Singh, Harinder P.; Roxburgh, Ian W.; Chan, Kwing L.
1996BASI...24..281S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar astrophysics: an overview
Authors: Roxburgh, Ian W.
1996BASI...24...89R 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: An asymptotic description of solar acoustic oscillation of
low and intermediate degree
Authors: Roxburgh, I. W.; Vorontsov, S. V.
1996MNRAS.278..940R Altcode:
We present an asymptotic description of high-frequency solar p modes
which permits an accurate treatment of regions where the seismic
parameters vary rapidly with depth, and incorporates the strong effect
of gravity perturbations on low-degree modes. The description is based
on an asymptotic reduction of the governing fourth-order system of
linear differential equations to second order. Approximate solutions
of the second-order equation are then developed using a Born-type
asymptotic expansion. The accuracy of the resulting description
is tested numerically on a standard solar model. Higher order Born
approximations give fractional accuracies of at least 10^-3. This is
approximately an order of magnitude better than results from an earlier,
more straightforward second-order analysis by Vorontsov.
---------------------------------------------------------
Title: STARS - Seismic Telescope for Astrophysical Research from
Space. Report on the phase A study.
Authors: Badiali, M.; Catala, C.; Favata, F.; Fridlund, M.; Frandsen,
S.; Gough, D. O.; Hoyng, P.; Pace, O.; Roca-Cortés, T.; Roxburgh,
I. W.; Sterken, C.; Volonté, S.
1996star.book.....B Altcode:
STARS is an asteroseismology mission, which, through the acquisition of
very accurate light curves, will detect oscillations in a wide variety
of stars. This will allow, for the first time, the internal structure
of stars of different age, composition and spectral type, to be studied
directly, bringing the spectacular successes of helioseismology within
reach for a large number of other stars spreading over most of the
Hertzsprung-Russell diagram, including solar-type stars in open
clusters. The results of the phase A study are presented in this report.
---------------------------------------------------------
Title: (Erratum) Limits on convective penetration from stellar cores.
Authors: Roxburgh, I. W.
1996A&A...306..336R Altcode:
Erratum to Astron. Astrophys. 226, 291-293 (1992).
---------------------------------------------------------
Title: On the Transport of Angular Momentum in Magnetic Stellar
Interiors
Authors: Ocaña, G.; Roxburgh, I. W.
1996ApL&C..34...29O Altcode:
No abstract at ADS
---------------------------------------------------------
Title: STARS: Seismic Telescope for Astrophysical Research from Space
Authors: Badiali, M.; Catala, C.; Favata, F.; Fridlund, M.; Frandsen,
S.; Gough, D. O.; Hoyng, P.; Pace, O.; Roca-Cortes, T.; Roxburgh,
I. W.; Sterken, C.; Volonte, A.
1996ESADS...4....1B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Gravitation experiment payloads for non dedicated space
missions. Report of the Columbus Metrology and Gravitation Science
Team
Authors: Spallicci, A.; Brillet, A.; Busca, G.; Fuligni, F.; Nobili,
A.; Roxburgh, I.
1996step.symp..382S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Upper limits on the cosmological gravitational wave background
and maser clocks in space
Authors: Polnarev, A. G.; Roxburgh, I. W.
1995GReGr..27..379P Altcode:
We consider the possibility of detecting gravitational waves through
the measurement of a time varying phase shift using a hydrogen maser
clock on a satellite. Such measurements enable us to put interesting
upper limits on the contribution of the gravitational-wave background
to the dimensionless density of the Universe. The requirements on
residual accelerations and the sensitivity of an accelerometer on
the spacecraft are shown to be realistic and could be achieved using
the accelerometer technology developed by ONERA for the ARISTOTELES
mission. Such an experiment placing upper limits on the cosmological
gravitational wave background could be conducted using the proposed
Russian satellite “Millimetron”.
---------------------------------------------------------
Title: Three-dimensional simulation of penetrative convection:
penetration below a convection zone.
Authors: Singh, H. P.; Roxburgh, I. W.; Chan, K. L.
1995A&A...295..703S Altcode:
We perform full three-dimensional numerical simulations to study
the behaviour of penetrative compressible convection below a deep
stratified stellar-type convective envelope. The domain of computations
is divided into three distinct regions; the upper 2% and the lower 40%
is kept convectivly stable while the middle 58% is made unstable to
convection. Four series of solutions have been computed by varying the
polytropic index and thus the stability of the lower stable layer. The
penetration distance is found to decrease as the stability of the
region beneath the convection zone is increased.
---------------------------------------------------------
Title: An asymptotic description of solar acoustic oscillations with
an elementary excitation source
Authors: Roxburgh, I. W.; Vorontsov, S. V.
1995MNRAS.272..850R Altcode:
We extend the asymptotic description of solar p-modes to include an
excitation source. The linear dynamic response of a star is considered
within the general framework of a Fourier transform of the source
function in time, and a vector spherical harmonic decomposition in
space. Quantitative analysis is developed for the linear response to an
`elementary' harmonic excitation source described by a delta-function
in the radial direction, using a simplified description of the energy
leakage from the acoustic cavity. The synthetic p-mode power spectra
are computed numerically for different depths of the excitation
source, and their simple properties are discussed. The asymptotic
eigenfrequency equation is generalized to describe the frequencies of
maximum amplitudes in the theoretical response function. The resulting
frequency equation with modified `surface phase shift' degenerates
into the standard eigenfrequency equation at low frequencies, and
describes the high-frequency `pseudo-modes' in the high-frequency
limit, joining both these well-known theoretical descriptions in the
intermediate frequency range.
---------------------------------------------------------
Title: Synthetic p-Mode Power Spectra with an Elementary Excitation
Source
Authors: Roxburgh, I. W.; Vorontsov, S. V.
1995ASPC...76..362R Altcode: 1995gong.conf..362R
No abstract at ADS
---------------------------------------------------------
Title: Convective Penetration in Stars (Abstract)
Authors: Roxburgh, I. W.; Simmons, J.; Singh, H. P.; Vorontsov, S. V.
1995LIACo..32..231R Altcode: 1995sews.book..231R
No abstract at ADS
---------------------------------------------------------
Title: Simulated Power Spectra of Solar-Type Oscillations Driven by
an Elementary Excitation Source
Authors: Roxburgh, I. W.; Vorontsov, S. V.
1995ASPC...83..111R Altcode: 1995IAUCo.155..111R; 1995aasp.conf..111R
No abstract at ADS
---------------------------------------------------------
Title: Physical Processes in Astrophysics
Authors: Roxburgh, Ian W.; Masnou, Jean-Louis
1995LNP...458.....R Altcode: 1995QB460.P48......
This volume, in honour of Evry Schatzman, contains in-depth reviews
on central topics of modern astrophysics, such as stellar physics,
covering stellar evolution, solar neutrinos, stellar rotation and spin
down, convection transport processes, neutron stars, white dwarfs, and
novae. All the talks were given by leading experts who had time both
to develop the basics of their subject and to cover recent work. The
volume is meant for both graduate students and researchers.
---------------------------------------------------------
Title: Quasi-Asymptotic Description of Adiabatic Acoustic Oscillations
Authors: Roxburgh, I. W.; Vorontsov, S. V.
1995ASPC...76..370R Altcode: 1995gong.conf..370R
No abstract at ADS
---------------------------------------------------------
Title: Overshooting from convective cores
Authors: Roxburgh, Ian W.
1995LNP...458..239R Altcode:
Convective overshooting increases the fraction of the star which is
effectively mixed, thus altering models of stellar evolution. If the
feed back of overshooting on the structure of the star is neglected
the estimated extent of overshooting is very small. If the feed back
is included in these estimates then the adiabatic core is extended by
a substantial fraction (of order 25%) of the radius of the unstable
region. An upper limit on convective overshooting is given by the
integral constraint (Roxburgh 1978, 1989) with viscous dissipation
neglected. For small cores this gives an increase in core mass of 50
85%. Numerical simulations of two-dimensional compressible convection in
a fluid where the central regions are naturally convectively unstable,
and the surrounding layers are stable, have been undertaken for
different values of the Prandtl number. The results indicate that for
low Prandtl numbers viscous dissipation is of decreasing importance
and the simple integral condition gives a reasonable estimate of the
extent of overshooting.
---------------------------------------------------------
Title: Seismology of the Solar Envelope - the Base of the Convective
Zone as Seen in the Phase Shift of Acoustic Waves
Authors: Roxburgh, I. W.; Vorontsov, S. V.
1994MNRAS.268..880R Altcode:
At the base of the convective zone, discontinuities in the derivatives
of the sound speed produce a phase shift in acoustic waves. This phase
shift, α<SUB>0</SUB>(ν), is inferred by matching the measured solar
p-modes to a second-order asymptotic description, the contribution
from the surface layers and the second helium ionization zone being
subtracted using modes with turning points well inside the convective
zone. The resulting phase shift varies quasi-periodically with
frequency with a period ≍220 μHz, and has an amplitude ≍8(±4)
× 10<SUP>-4</SUP> at a frequency of 3000 μHz. The phase shift
α<SUB>0</SUB>(ν) is also calculated using the same technique for
two solar models, one with no convective penetration and one with
penetration extending for 1 per cent of the solar mass. <P />We
estimate the predicted phase shift for models of the convective zone,
including possible convective penetration modelled by extending the
zone a distance ɛH<SUB>p</SUB> below the classical boundary; α(ν)
has a quasi-periodic contribution with period ≍1/(2τ<SUB>β</SUB>),
where τ<SUB>β</SUB> = ∫ dr/c is the acoustic depth of the base of
the zone, and with amplitude where f(ɛ) and h(ɛ) are functions of
ɛ which also depend on the variation of opacity with temperature
and density. For ν = 3000 μHz, and typical values at the base
of the convective zone, A<SUB>V</SUB> = 5& × 10<SUP>-4</SUP>
for ɛ = 0, decreases slightly for small ɛ and then increases to
1 × 10<SUP>-3</SUP> for ɛ = 0.25, and to 1.7 × 10<SUP>-3</SUP>
for ɛ = 0.5. <P />The currently available data are consistent with
an overshooting parameter 0≤ɛ≤0.25.
---------------------------------------------------------
Title: The Asymptotic Theory of Stellar Acoustic Oscillations -
a Fourth-Order Approximation for Low-Degree Modes
Authors: Roxburgh, I. W.; Vorontsov, S. V.
1994MNRAS.268..143R Altcode:
The asymptotic description of low-degree stellar acoustic modes
is extended to fourth order in inverse powers of the cyclical
frequency. The accuracy of the asymptotic approximation is tested
by comparing the predicted values of the eigenfrequencies and the
`small frequency separations' with those calculated by solving the
full equations governing the adiabatic oscillations of a standard
solar model.
---------------------------------------------------------
Title: The seismology of stellar cores: a simple theoretical
description of the small frequency separations.
Authors: Roxburgh, I. W.; Vorontsov, S. V.
1994MNRAS.267..297R Altcode:
We present a new theoretical description of the 'small frequency
separations' delta omega<SUB>l, n</SUB> = omega<SUB>l, n</SUB> -
omega<SUB>l + 2, n - 1</SUB> for high-frequency stellar p-modes of
low degree, these separations being the observable quantities that are
primarily sensitive to the structure of the deep stellar interior. The
description is based on an integral representation of the phase shift
of acoustic waves due to scattering off the stellar core, taking into
account the effects of buoyancy and gravitational perturbations. The
accuracy of the theoretical description is tested by comparing the
predicted frequency separations with values determined by numerically
solving the full set of eigenfrequency equations for a standard solar
model and for simple zero-age and evolved models of a 3-solar mass
main-sequence star with a convective core.
---------------------------------------------------------
Title: Three-dimensional simulation of penetrative
convection-penetration above a convection zone
Authors: Singh, Harinder P.; Roxburgh, Ian W.; Chan, Kwing L.
1994A&A...281L..73S Altcode:
We study the general behavior of three-dimensional penetrative
convection of deep stellar-type envelopes. The convectively unstable
region may be bounded from above and below by stable layers. We confine
our attention at present to the penetration into the upper stable
layer. To achieve this the unstable layer is made appreciably thick
and sufficient room is provided for penetration above this layer. We
perform the numerical experiment for five different cases covering a
range of control parameters including stratification and the total flux
flowing through the region. Although we find a noticable penetration
region above the convective layer in all the cases, the penetration
distance is found to increase with the factor (flux / density at the
top of the convective layer).
---------------------------------------------------------
Title: IRIS VI
Authors: Gough, D. O.; Roxburgh, I. W.
1994iris.conf.....G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Overshooting from convective cores: theory and numerical
simulation.
Authors: Roxburgh, I. W.
1994ems..conf..299R Altcode:
Convective overshooting increases the fraction of the star which is
effectively mixed, thus altering models of stellar evolution. If the
feed back of overshooting on the structure of the star is neglected
the estimated extent of overshooting is very small. If the feed back
is included in these estimates then the adiabatic core is extended by
a distance comparable to a substantial fraction of the radius of the
unstable region. An upper limit on convective overshooting is given by
the integral constraint (Roxburgh 1978, 1989) with viscous dissipation
neglected. If this constraint is applied to small convective cores then
the maximum extent of the penetration region is shown to be at most
about 0.18 times the radius of the core independent of the details of
energy generation and opacity. The ratio of the maximum penetration
distance to the scale height at the edge of the "classical boundary"
varies very strongly with core size, and modelling overshooting by
taking the penetration distance as a multiple of the scale height
is likely to give misleading results. Numerical simulations of
two-dimensional compressible convection in a fluid where the central
regions are naturally convectively unstable, and the surrounding
layers are stable, have been undertaken for different values of the
Prandtl number. The results indicate that for low Prandtl numbers
viscous dissipation is of decreasing importance and the simple
integral condition gives a reasonable estimate of the extent of
overshooting. Stellar seismology offers the possibility of detecting
the location of the core-envelope interface through a periodic variation
of the small frequency separation with frequency.
---------------------------------------------------------
Title: Equivalence principle, constant of gravitation, special and
general relativity experiments in the COLUMBUS space programme
Authors: Spallicci, A.; Brillet, A.; Busca, G.; Fuligni, F.; Nobili,
A.; Roxburgh, I.
1993CQGra..10S.259S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Structure and Secular Stability of Plane-Parallel
Stellar Objects
Authors: Roxburgh, I. W.
1993MNRAS.264..636R Altcode:
The structure of self-gravitating, plane-parallel, vertically
stratified stellar objects, with the energy generation and opacity
given by the power laws ɛ = ɛ<SUB>0</SUB>ρT<SUP>η</SUP>, κ =
κ<SUB>0</SUB>ρ<SUP>α</SUP>T<SUP>-β</SUP>, is studied. It is
shown that the condition for secular stability in such objects is 5 +
α + β - η > 0, whereas for spherical stars the corresponding
condition is η + β -3 -3α > 0. Exact solutions (in closed form)
are presented both for fully radiative models and for models with a
convective central region. Approximate analytic solutions are given
for models with a convective central region and radiative outer
layers. Numerical models are readily calculated.
---------------------------------------------------------
Title: On the Generation of the Largescale and Turbulent Magnetic
Fields in the Solar Type Stars
Authors: Durney, Bernard R.; De Young, David S.; Roxburgh, Ian W.
1993SoPh..145..207D Altcode:
It is thought that the large-scale solar-cycle magnetic field is
generated in a thin region at the interface of the radiative core
(RC) and solar convection zone (SCZ). We show that the bulk of the SCZ
virogoursly generates a small-scale turbulent magnetic field. Rotation,
while not essential, increases the generation rate of this field.
---------------------------------------------------------
Title: Overshooting from convective cores: Theory and numerical
simulation
Authors: Roxburgh, Ian W.
1993SSRv...66..299R Altcode:
Convective overshooting increases the fraction of the star which is
effectively mixed, thus altering models of stellar evolution. If the
feed back of overshooting on the structure of the star is neglected
the estimated extent of overshooting is very small. If the feed back
is included in these estimates then the adiabatic core is extended
by a distance comparable to a substantial fraction of the radius
of the unstable region. An upper limit on convective overshooting
is given by the integral constraint (Roxburgh 1978, 1989) with
viscous dissipation neglected. If this constraint is applied to
small convective cores then the maximum extent of the penetration
region is shown to be at most about 0.18 times the radius of the core
independent of the details of energy generation and opacity. The ratio
of the maximum penetration distance to the scale height at the edge of
the “classical boundary” varies very strongly with core size, and
modelling overshooting by taking the penetration distance as a multiple
of the scale height is likely to give misleading results. Numerical
simulations of two-dimensional compressible convection in a fluid
where the central regions are naturally convectively unstable,
and the surrounding layers are stable, have been undertaken for
different values of the Prandtl number. The results indicate that for
low Prandtl numbers viscous dissipation is of decreasing importance
and the simple integral condition gives a reasonable estimate of the
extent of overshooting. Stellar seismology offers the possibility of
detecting the location of the core — envelope interface through a
periodic variation of the small frequency separation with frequency.
---------------------------------------------------------
Title: Seismology of the Solar Envelope - the Base of the Convective
Zone as Seen in the Phase Shift of Acoustic Waves
Authors: Roxburgh, I. W.; Vorontsov, S. V.
1993ASPC...42..169R Altcode: 1993gong.conf..169R
No abstract at ADS
---------------------------------------------------------
Title: Integral Constraints On Convective Overshooting -
Two-Dimensional Numerical Studies
Authors: Roxburgh, Ian W.; Simmons, John
1993ASPC...40..290R Altcode: 1993ist..proc..290R; 1993ASPC...40..290M
No abstract at ADS
---------------------------------------------------------
Title: Convective Overshooting in Stars
Authors: Narasimha, D.; Roxburgh, I. W.
1993ASPC...42...73N Altcode: 1993gong.conf...73N
No abstract at ADS
---------------------------------------------------------
Title: Asymptotic theory of low-degree stellar acoustic oscillations
Authors: Roxburgh, I. W.; Vorontsov, S. V.
1993ASPC...40..535R Altcode: 1993ist..proc..535R; 1993IAUCo.137..535R
No abstract at ADS
---------------------------------------------------------
Title: Key issues - A round table discussion
Authors: Brown, T. M.; Demarque, P.; Noyes, R.; Praderie, F.; Roxburgh,
I. W.; Schatzman, E.
1993ASPC...40..776B Altcode: 1993ist..proc..776B; 1993IAUCo.137..776B
An overview of a round table discussion on the internal dynamics of
stars, some problems in stellar structure and evolution, a study of
stellar activity mechanisms using PRISMA, the seismology of sunlike
stars, and directions of future research is presented. It is concluded
that models that take into account just one physical process generally
do not agree with the observations. This provides evidence for the
presence of other physical processes. In each phenomenon which is
considered, a variety of physical processes are involved. All physical
processes should be taken into account simultaneously. Stars need to
be considered globally. It is recommended that attention be given to
such unsolved problems as the helium content of the sun, the abundance
of lithium in fast rotating stars, and the origin and evolution of
stellar magnetic fields.
---------------------------------------------------------
Title: Post Newtonian limit of Finsler space theories of gravity
and solar system tests.
Authors: Roxburgh, I. W.
1993rges.conf..500R Altcode: 1993rges.rept..500R
The properties of generalised Finsler spaces are discussed. The post
Newtonian limit for the strongly spherically symmetric one-body problem
is considered by expanding the Finsler space about the Minkowski space
of Special Relativity. In a Finsler space the second order gravitational
red-shift experiment need not give the same values of PPN parameters
as are obtained from time delay and perihelion advance. Thus a second
order red-shift experiment would help test the Riemannian metric
hypothesis of General Relativity.
---------------------------------------------------------
Title: The Phase Shift of Low L-Modes due to the Helium Ionisation
Zone and the Base of the Convective Envelope
Authors: Roxburgh, I. W.
1993ASPC...42..173R Altcode: 1993gong.conf..173R
No abstract at ADS
---------------------------------------------------------
Title: Limits on convective penetration from stellar cores
Authors: Roxburgh, I. W.
1992A&A...266..291R Altcode:
The Integral Constraint on convective penetration gives an upper limit
on the extent of convective penetration. If this is applied to small
convective cores then the maximum extent of the penetration region is
shown to be at most about 0.18 times the radius of the core independent
of the details of energy generation and opacity. For larger cores
the penetration distance depends on the particular properties of the
nuclear reactions and opacity. Using simple power law approximations for
the energy generation and opacity, the upper bound to the penetration
distance is found to be approximately 0.2 of the core radius, and the
core mass to be about 1.8 times the value without penetration, for a
range of conditions and core sizes. The ratio of the maximum penetration
distance to the scale height at the edge of the 'classical boundary'
varies very strongly with core size, and modelling penetration by taking
the penetration distance as a multiple of the scale height is likely
to give misleading results. This is especially true for small cores
such as exist in the early stages of the evolution of solar type stars.
---------------------------------------------------------
Title: Post-Newtonian limit of Finsler space theories of gravity
and solar system tests
Authors: Roxburgh, Ian W.
1992GReGr..24..419R Altcode:
Finsler geometry is considered as a wider framework for analysing solar
system tests of theories of gravity than is afforded by Riemannian
geometry. The post-Newtonian limit for the spherically symmetric
one-body problem is examined by expanding the Finsler metric about the
Minkowski space of Special Relativity for those Finsler spaces whose
null surface is Riemannian. In such a framework there are five PPN
parameters instead of the three in Riemannian geometry. The classical
solar system tests can readily be satisfied leaving two arbitrary
parameters. These parameters could be determined from measurements of
the second order gravitational red-shift and periodic perturbations in
particle orbits, thus providing a consistency check on the Riemannian
metric hypothesis of General Relativity. Such an experiment is possible
on a satellite on an orbit with perihelion of a few solar radii.
---------------------------------------------------------
Title: Proceedings of Columbus Metrology Science Team
Authors: Brillet, A.; Busca, G.; Fuligni, F.; Nobili, A.; Roxburgh,
I.; Spallicci, A.
1991cms2.meet....1B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Proceedings of Columbus Metrology Science Team
Authors: Brillet, A.; Busca, G.; Fuligni, F.; Nobili, A.; Roxburgh,
I.; Spallicci, A.
1991cms1.meet....1B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Finsler spaces with Riemannian geodesics
Authors: Roxburgh, Ian W.
1991GReGr..23.1071R Altcode:
In Finsler spaces the intervalds=F(x <SUP> i </SUP>,dx <SUP> i
</SUP>) is an arbitrary function of the coordinatesx <SUP> i </SUP>
and coordinate incrementsdx <SUP> i </SUP> withF homogeneous of degree
one in thedx <SUP> i </SUP>. It is shown that for Riemannian spacesds
<SUB> R </SUB> <SUP>2</SUP>=g <SUB> ij </SUB> dx <SUP> i </SUP> dx <SUP>
i </SUP> which admit a non trivial covariantly constant tensorH <SUB>
i </SUB>.(x <SUP> k </SUP>) there is an associated Finsler space with
the same geodesic structure. The subset of such Finsler spaces withH
<SUB> i </SUB>.(x <SUP> k </SUP>) a vector or second rank decomposable
tensor is determined.
---------------------------------------------------------
Title: Differential Rotation of Fully Convective Pre-Main Sequence
Stars
Authors: Roxburgh, I. W.
1991ASIC..340...83R Altcode: 1991amey.conf...83R
No abstract at ADS
---------------------------------------------------------
Title: Angular Momentum Transport Rotational Instabilities Magnetic
Fields and Mixing
Authors: Roxburgh, I. W.
1991ASIC..340..365R Altcode: 1991amey.conf..365R
No abstract at ADS
---------------------------------------------------------
Title: Convective Cores in Stellar Models
Authors: Roxburgh, I. W.; Monteiro, M.
1991LNP...380...95R Altcode: 1991IAUCo.130...95R; 1991sacs.coll...95R
The condition for homogeneous radiative stellar models to be marginally
stable to convection at the centre is investigated for the family
of models where the opacity and energy generation are given by power
laws in temperature and density = K0 T-, = 0 Tη. The Naur-Osterbrock
(1953) condition 6η > 6 + 10β - 15α is a necessary but not
sufficient condition. A better estimate is obtained by taking the
effective polytropic index n = dlogP/dlogT - 1 to be a linear function
of temperature T throughout the model. This gives the condition
<tbody> & <P />$6eta = 10beta - 15alpha + frac{{12 + 4beta
}}{{1 + alpha }}$ <P />;
---------------------------------------------------------
Title: Challenges to Theories of the Structure of Moderate-Mass Stars
Authors: Roxburgh, Ian W.
1991LNP...388..411R Altcode: 1991ctsm.conf..411R
No abstract at ADS
---------------------------------------------------------
Title: Comparison of Solar Models with Los Alamos and Livermore
Opacities
Authors: Roxburgh, Ian W.
1991LNP...388...57R Altcode: 1991ctsm.conf...57R
Models of the present sun were computed using the Los Alamos and the new
Livermore opacities. The relative abundance abundance of heavy elements
was the Grevesse mixture and the ratio Z/X was taken as 0.02765. The
models were iterated to have R = Rsun and L = Lsun at an age of to =
4.6 109 years. The differences between the two models are presented.
---------------------------------------------------------
Title: Variability in the Solar Output
Authors: Roxburgh, I. W.
1990RSPTA.330..641R Altcode:
Evidence for variability in the solar output is briefly discussed. If
the solar neutrino flux and the solar oscillation frequencies vary
over a solar cycle this could indicate that the solar cycle has its
origin in the solar core rather than be due to dynamo action in the
solar convective zone.
---------------------------------------------------------
Title: The Newton mission - a proposed manmade planetary system in
space to measure the gravitational constant.
Authors: Nobili, A. M.; Milani, A.; Polacco, E.; Roxburgh, I. W.;
Barlier, F.; Aksnes, K.; Everitt, C. W. F.; Farinella, P.; Anselmo,
L.; Boudon, Y.
1990ESAJ...14..389N Altcode:
A space mission is described which consists of a rigid
spin-axis-stabilised spacecraft with two small, high-density masses
free-falling inside. The gravitational attraction of the masses
dominates all perturbations, providing a miniature "planet-satellite"
system that can only be realised in space. Unlike any celestial
two-body system, the masses can be weighed on Earth before launch. Thus,
monitoring their motion by means of an inward-looking tracking camera
allows the value of the universal constant of gravity, G, to be
determined. A careful analysis of all perturbing forces shows that
G can be measured at least to 1 part in 10<SUP>5</SUP>, and perhaps
even somewhat better.
---------------------------------------------------------
Title: Variability in the solar output.
Authors: Roxburgh, I. W.
1990ecvs.conf..641R Altcode:
Evidence for variability in the solar output is briefly discussed. If
the solar neutrino flux and the solar oscillation frequencies vary
over a solar cycle this could indicate that the solar cycle has its
origin in the solar core rather than be due to dynamo action in the
solar convective zone.
---------------------------------------------------------
Title: Integral constraints on convective overshooting
Authors: Roxburgh, I. W.
1989A&A...211..361R Altcode:
The integral constraint used to estimate the uncertainty in present
knowledge of convection and convective overshooting is rederived for the
general compressible case and shown to reduce to the previous result
for almost adiabatically stratified convective zones when viscous
dissipation is neglected. It is further shown that the objections by
Baker and Kuhfuss (1987) require the stratification to be strongly
nonadiabatic and that this then renders invalid standard models of
stellar structure. Evidence from solar oscillations does not indicate
such a large departure from adiabaticity.
---------------------------------------------------------
Title: Future research on close binaries.
Authors: Roxburgh, I. W.
1988covp.conf..469R Altcode:
Short conference summary.
---------------------------------------------------------
Title: Problems of the Solar Interior
Authors: Roxburgh, Ian W.
1987ASSL..137....1R Altcode: 1987isav.symp....1R
The 'standard model' of the sun is discussed and it is noted that the
initial burning of He-3 and C-12 may produce a central convective core
which may be sustained for some time by convective overshooting. In
effect, g modes of oscillation may be excited by the He-3 and C-12
profiles which may also influence evolution. The solar neutrino problem
is studied in detail together with the He-3 instability, convective
overshooting, and internal rotation.
---------------------------------------------------------
Title: The internal rotation of the Sun.
Authors: Roxburgh, Ian W.
1986ASIC..169..249R Altcode: 1986ssds.proc..249R
Recent results on the internal rotation of the Sun are difficult
to explain. These problems are reviewed and it is conjectured that
a <SUP>3</SUP>He driven mixed shell near 0.3 R_sun; magnetically
separates the inner core from the outer regions. Such a shell may
rotate differentially and may separate a more rapidly spinning core
from the rest of the Sun.
---------------------------------------------------------
Title: Simulation of General Relativistic Corrections in Longterm
Numerical Integrations of Planetary Orbits
Authors: Nobili, Anna; Roxburgh, Ian W.
1986IAUS..114..105N Altcode: 1986rcma.conf..105N
Long term numerical integrations of planetary orbits designed to study
the stability of the Solar System over timescales comparable to its age
have become very promising thanks to the availability of very powerful
computers and to a substantial improvement in methods of investigating
the stability of hierarchical dynamical systems. The stability of such
numerical integrations relies on the ability to control all possible
sources of error. Among the errors caused by the inadequacy of the
physical model are those due to the fact that Newton's theory of
gravitation is used instead of general relativity. It is shown that
the secular advance of perihelia predicted by general relativity can
be simulated exactly by a 1/r-squared perturbing potential with almost
negligible additional cost in computer time.
---------------------------------------------------------
Title: Finite amplitude limit of the <SUP>3</SUP>He instability.
Authors: Roxburgh, I. W.
1986ASIC..169..265R Altcode: 1986ssds.proc..265R
The models of solar type stars are unstable to non-radial oscillations
driven by burning <SUP>3</SUP>He. These oscillations modify the
distribution of <SUP>3</SUP>He leading to finite amplitude oscillations
with typical temperature perturbations δT/T≡0.1.
---------------------------------------------------------
Title: Sound speed in the interior of solar models
Authors: Roxburgh, I. W.
1986ASIC..169..121R Altcode: 1986ssds.proc..121R
No abstract at ADS
---------------------------------------------------------
Title: Present Problems of the Solar Interior
Authors: Roxburgh, I. W.
1985SoPh..100...21R Altcode:
The standard model of solar evolution is reviewed and a number
of problems highlighted. A fundamental question is whether there
is any mixing of matter in the central regions, since such mixing
could radically alter the model of the present Sun and modify our
understanding of the evolution of other stars. Standard models
of solar evolution become unstable to <SUP>3</SUP>He driven global
oscillations at an age of 3 × 10<SUP>8</SUP> years and this may drive
some mixing, even if this is not the case the finite amptitude limit of
these oscillations is likely to produce modifications in the standard
model. Convective overshooting at the bottom of the outer convective
zone leads to an increased depth of this zone and small changes in the
interior. It is pointed out that the young Sun had a <SUP>12</SUP>C
driven convective core whose extent and duration depends on the extent
of overshooting. Such a core is likely to produce a magnetic field which
will affect the internal dynamics. The internal rotation of the Sun
remains an enigma and absence of knowledge of any internal magnetic
field makes it difficult to study the problem. Rotationally driven
instabilities are ineffective in the central chemically inhomogenous
regions but may contribute to the inward diffusion of lithium from
the convective zone. These and other problems are considered, but few
solutions are proposed.
---------------------------------------------------------
Title: Instabilities, mixing and solar neutrinos
Authors: Roxburgh, I. W.
1985AIPC..126...88R Altcode: 1985snna.proc...88R
Instabilities driven by differential rotation during spin down of
a rotating solar model are analysed and it is shown that with a very
small composition gradient, the first unstable mode is the Axisymmetric
Baroclynic Diffusive (ABCD) instability. It is argued that if this
instability occurs, it leads to an almost horizontal re-adjustment of
chemical composition and only very slight mixing. <P />Mixing due to
the 3He instability is energetically possible but it is argued that
finite amplitude oscillations lead to a quasi-steady state without
mixing with 3He being burnt to 4He during such oscillations.
---------------------------------------------------------
Title: Report of IAU Commission 49: The interplanetary plasma and
the heliosphere (Plasma interplanétaire et l'héliosphère).
Authors: Roxburgh, I. W.
1985IAUTA..19..697R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Rotational instabilities in the solar interior turbulent
diffusion and the solar neutrino problem
Authors: Roxburgh, I. W.
1984MmSAI..55..273R Altcode:
The sun is losing angular momentum through the mass loss in the solar
wind and must therefore have spun down from higher velocities during
its lifetime. This angular momentum loss will produce differential
rotation in the solar interior unless magnetic fields are retained in
the interior and are able to transport angular momentum by magnetic
stresses. In this paper the author assumes magnetic fields are not
effective in the bulk of the interior and shows that when the radial
angular velocity reaches a critical value, baroclynic overstability sets
in. This instability drives the inward diffusion of <SUP>1</SUP>H. The
increase of the central <SUP>1</SUP>H abundance will lead to a reduction
of the detectable neutrino flux.
---------------------------------------------------------
Title: On the Tassoul Approximation Scheme for Determining the
Structure of Rotating Stars
Authors: Roxburgh, I. W.
1984IAUS..105..517R Altcode:
The method used by Tassoul and Tassoul assumes a "turbulent viscosity"
which is important in determining the dynamics, but is unimportant in
heat transport. This approximation is shown to be inconsistent.
---------------------------------------------------------
Title: On Turbulent Mixing
Authors: Roxburgh, I. W.
1984IAUS..105..519R Altcode:
Several authors have suggested that turbulent mixing takes place in
some, if not all, stars, and in particular that such mixing can explain
the low solar neutrino flux. This turbulence is thought to be caused
by differential rotation produced by braking due to angular momentum
loss in a stellar wind, and/or to the effect of meridional circulation
currents in redistributing angular momentum. Whilst such instabilities
may exist even in the presence of a stabilizing distribution of chemical
composition, they do not necessarily cause mixing. To be effective in
mixing, the energy available to the instability be it differential
rotation or any other mechanism, has to be sufficient to lift the
helium rich matter in the interior of the star to the outer regions.
---------------------------------------------------------
Title: Magnetic Fields and Angular Momentum Loss
Authors: Gill, R. S.; Roxburgh, I. W.
1984srps.conf..335G Altcode:
Angular momentum loss rates are calculated for stars with dipole
and quadrupole magnetic fields, and isothermal coronae. The angular
momentum loss rate for dipole fields is found to be considerably higher
than that for quadrupole fields. If the dynamo produced magnetic field
changes from quadrupole to dipole as the angular velocity decreases,
there should be a sudden increase in the rate of angular momentum
loss. The resulting decrease in the angular velocity with time is
calculated assuming that the stars rotate uniformly throughout and used
to determine the predicted distribution of angular velocity amongst
stars of the same mass. This distribution has two peaks in qualitative
agreement with the observations of Vaughan.
---------------------------------------------------------
Title: Space experiments in relativity and gravitation.
Authors: Roxburgh, I. W.
1984ESASP1070...84R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Internal rotation of the Sun
Authors: Spruit, H. C.; Knobloch, E.; Roxburgh, I. W.
1983Natur.304..520S Altcode:
The low surface rotation rate of the Sun and other main-sequence
stars is believed to be the result of angular momentum loss due to
a stellar wind<SUP>1</SUP>. This loss also leads to a differential
rotation, the interior spinning more rapidly than the surface. The
rate of increase with depth of the rotation speed is limited by
hydrodynamic instabilities, which cause an outward diffusion of
angular momentum<SUP>2</SUP>. The conditions for the occurrence of
hydrodynamic instabilities in a radiative stellar interior are reviewed
here assuming that the rotation is constant on spheres. The instability
with the lowest threshold is a double diffusive one, the axisymmetric
baroclinic diffusive (ABCD) instability. A minimum rotation curve for
the present Sun is calculated using the assumption that the efficiency
of this instability is sufficiently high that the rotation of the
Sun is close to marginal stability. This lower limit to the internal
rotation rate is roughly consistent with present observations of the
rotational splitting of solar oscillations.
---------------------------------------------------------
Title: Stellar winds and spindown in solar type stars
Authors: Roxburgh, I. W.
1983IAUS..102..449R Altcode:
A simple model of stellar wind-induced angular momentum loss is
presented in which the field is potential when the flow speed is lower
than the Alfven speed, and radial when greater. The consequence, an
increasing angular momentum loss rate with increasing simplicity of
the magnetic geometry, is used to explain the rotational discontinuity
across the Vaughan-Preston gap as due to a sudden angular momentum
loss when the dynamo field switches from quadrupole to dipole
geometry. Attention is given to the evolution of the internal rotation
of stars as a result of surface angular momentum loss, and to recent
results on solar oscillation rotational splitting which suggest that
the inside of the sun is spinning faster than the surface.
---------------------------------------------------------
Title: Microinstabilities and Models of the Solar Wind
Authors: Rowse, D. P.; Roxburgh, I. W.; Schwartz, S. J.
1981SoPh...74..179R Altcode:
The collision-dominated two-fluid plasma models of the solar wind are
shown to become collisionless and subject to microinstabilities at a few
solar radii. Assuming that once the plasma is unstable it stays close to
marginal stability models of the solar wind are constructed including
waves and proton heating. The resulting models have higher velocities
and proton temperatures than the collision dominated two fluid models.
---------------------------------------------------------
Title: Modelling Coronal Magnetic Fields
Authors: Rowse, D. P.; Roxburgh, I. W.
1981SoPh...74..165R Altcode:
The `hairy ball' model of coronal magnetic fields has a spherical source
surface separating potential and radial magnetic fields. In the present
model the source surface is chosen such that the wind speed equals the
Alfvénic speed at selected points on the source surface. Results have
been obtained for a dipole base field and an isothermal corona.
---------------------------------------------------------
Title: Solutions of the Two-Fluid Solar Wind Equations - Adiabatic
and Conduction Dominated Solutions
Authors: Rowse, D. P.; Roxburgh, I. W.
1981SoPh...74..169R Altcode:
The equations governing the two-fluid spherically symmetric models
of the solar wind have been solved numerically for a wide range of
base conditions. As predicted from an asymptotic analysis we find
a whole domain of solutions which are asymptotically adiabatic with
the proton and electron temperatures tending to equality and varying
like r<SUP>- 4/3</SUP>. In these 4/3 solutions the electron and proton
heat conduction is asymptotically negligible and if it is neglected
the resulting equations can be integrated analytically and shown to
have the 4/3, 4/3 behaviour.
---------------------------------------------------------
Title: Solar Neutrinos
Authors: Roxburgh, I. W.
1981IrAJ...15..106R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar physics at Oxford
Authors: Roxburgh, I. W.; Jordan, C.
1981Natur.292..194R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The solar neutrino problem.
Authors: Roxburgh, I. W.
1981ASIC...68..399R Altcode: 1981spss.conf..399R
No abstract at ADS
---------------------------------------------------------
Title: Long Term Variations of the Solar Constant
Authors: Roxburgh, I. W.
1981sucl.conf..261R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Internal structure of the sun and stars.
Authors: Roxburgh, I. W.
1981ASIC...68...59R Altcode: 1981spss.conf...59R
The current theory of the internal structures of the sun and other
main-sequence stars is reviewed in light of the importance of structural
factors to the calculation of stellar luminosities and effective
temperatures. The basic physics of stellar interiors is discussed
based on a picture of stellar equilibrium supported by the balancing
of self-gravitation against the internal pressure generated by fusion
reactions, which act as a source of energy radiated or convected to
the surface. Simple stellar models are examined, and the importance of
convective effects, which are usually modelled by mixing length theory,
is emphasized. The evolution of stellar structure in its pre-main
sequence, main sequence and post-main sequence stages is then surveyed
and problems in the understanding of the details of stellar structure
are pointed out.
---------------------------------------------------------
Title: The Solar Neutrino Problem
Authors: Roxburgh, I. W.
1981sucl.conf..269R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A 'fast' model of the solar convection zone
Authors: Belvedere, G.; Paterno, L.; Roxburgh, I. W.
1980A&A....91..356B Altcode:
A model of solar convection zone incorporates the mixing-length theory
in the method developed by Faulkner (1965) which accurately represents
the superadiabatic layers. Interpolation formulas which save computer
time, and are sufficiently accurate to limit discrepancies in pressure
distribution and density through the convection zone, are used; the
computer programs are 20 times faster than the programs of Baker and
Temesvary (1966).
---------------------------------------------------------
Title: Instabilities in the Solar Wind
Authors: Schwartz, S. J.; Roxburgh, I. W.
1980RSPTA.297..555S Altcode: 1980RSLPT.297..555S
We review recent progress in the possible role of microturbulence
in the solar wind. The solar wind is expected to excite plasma
microinstabilities owing to its transition from a collision-dominated
to a collisionless plasma, with potentially drastic consequences
for thermal transport and other physical processes. We discuss both
the extensive linear theory of this subject and also our present
understanding of nonlinear plasma turbulence. The solar wind is an
excellent laboratory for studying many aspects of solar and plasma
physics, and may soon provide some answers to several fundamental
questions.
---------------------------------------------------------
Title: The origin of supergranulation and giant cells in the solar
convective zone.
Authors: Roxburgh, I. W.; Tavakol, R. K.
1979SoPh...61..247R Altcode:
In the standard model of the solar convective zone, turbulent eddies
transport entropy rather than temperature. We consider the turbulent
mean field equations for the convective zone, including entropy
transport, and show that the zone can be unstable to larger scale
motion which we identify with the supergranulation and giant cells.
---------------------------------------------------------
Title: Non-Riemann geometrizable effects in the gravitational
one-body problem.
Authors: Roxburgh, I. W.; Tavakol, R. K.
1979GReGr..10..307R Altcode:
We consider the question of whether the “correct” theory of
gravity is a metric theory. The metric hypothesis is shown to place
severe restrictions on the form of the equation of motion for the
one-body problem. By relaxing these restrictions we include nonmetric
contributions to the equation of motion, and the solution in the
post-Newtonian approximation is given. The solution given here
contains five arbitrary parameters in place of the usual two (β,
γ) of metric theories. One of them produces a secular change in the
eccentricity; the others contribute to the perihelion advance and to
periodic terms. Only certain combinations of these parameters can be
determined even from orbits with different eccentricities.
---------------------------------------------------------
Title: The internal structure of the sun and solar type stars.
Authors: Roxburgh, I. W.
1979psa..conf..243R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: European Space Agency studies of the solar probe
Authors: Roxburgh, I. W.
1978clus.nasa..556R Altcode:
The feasibility and scientific objectives of a solar probe were studied
by a Mission Definition Group in 1975 and 1976. The orbit analysis
program was developed and an extended study of the orbit analysis
was done in 1977. The results of these studies are in the Report of
the Mission Definition Study (1976) and an E.S.O.C. report (1978),
and the reader is referred to these sources for greater details. In
this report, only brief discussion on mission concept and objectives,
satellite design, orbit, orbit analysis, are presented.
---------------------------------------------------------
Title: The importance of determining the solar quadrupole moment
Authors: Roxburgh, I. W.
1978clus.nasa...11R Altcode:
Current theoretical modelling of the sun is in difficulty. Additional
observations must be made to place constraints on the plethora of
conjectures that have been advanced to explain the low neutrino flux
and to guide solar model builders in their search to understand the
deep interior of the sun. A determination of the magnitude of the
solar quadrupole moment, is one such constraint; it places limits on
the density, angular velocity and magnetic field distributions inside
the sun.
---------------------------------------------------------
Title: Convection and stellar structure.
Authors: Roxburgh, I. W.
1978A&A....65..281R Altcode:
The 'theory' of convection used to model stellar convective zones
neglects the flux of turbulent kinetic energy and is therefore only
applicable to zones that are small compared to a scale height,
yet the resulting models have convective zones that are several
scale heights thick. In this paper we attempt to quantify the error
involved by retaining the kinetic energy flux and assuming that the
viscous dissipation is small. This 'theory' leads to a new criterion to
determine the extent of convective zones which requires the convection
to penetrate into the surrounding stable layers. This new criterion
is used in constructing models of main sequence stars, the convective
cores in these stars are found to have 50-70% more mass than the old
models and slightly lower luminosities so extending the main sequence
phase of stellar evolution by up to 70% over previous estimates.
---------------------------------------------------------
Title: The Structure of Close Binaries
Authors: Roxburgh, I. W.; Williams, P. S.
1978Ap&SS..54..199R Altcode:
A method for calculating the structure of a close binary component is
presented. It is seen that the effect of binary distortion is to shift
the zero age main sequence to the right. Attempts to construct contact
systems with these models confirm the results of earlier workers that
this is not possible.
---------------------------------------------------------
Title: Origin of planetary nebulae
Authors: Roxburgh, I. W.
1978IAUS...76..295R Altcode:
The origin of planetary nebulae is discussed from the viewpoint
of healthy scepticism about theoretical models used in stellar
physics. The hypothesis that luminous red giants are the progenitors
of planetary nebulae is adopted, and predictions of stellar evolution
theory concerning the internal structure and evolution of stars from
the main sequence to the giant phase are summarized. Uncertainties in
these calculations are examined, particularly with regard to turbulent
convection, coronal-driven mass loss, rotation, magnetic fields, the
opacity of stellar material, neutrino energy losses, and dynamical
phases. Various proposed theories of nebula ejection are reviewed,
and the possibility of binary-star remnants of planetary nebulae
is considered.
---------------------------------------------------------
Title: The Solar Interior
Authors: Roxburgh, I. W.
1978pfsl.conf...21R Altcode: 1978ESPM....2...21R
No abstract at ADS
---------------------------------------------------------
Title: Solar Neutrinos and the Solar Interior
Authors: Roxburgh, I. W.
1978sfsn.conf..207R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Microturbulence and the Solar Wind
Authors: Schwartz, S. J.; Roxburgh, I. W.
1978pfsl.conf..317S Altcode: 1978ESPM....2..317S
No abstract at ADS
---------------------------------------------------------
Title: Multicell Convection in the Solar Envelope
Authors: Tavakol, R. K.; Roxburgh, I. W.
1978pfsl.conf...63T Altcode: 1978ESPM....2...63T
No abstract at ADS
---------------------------------------------------------
Title: Meridional circulation in the surface layers of rotating stars.
Authors: Smith, B. L.; Roxburgh, I. W.
1977A&A....61..747S Altcode:
The influence of self-inertia on the meridional circulation in the
radiative envelopes of rotating early-type stars is examined. It
is found that the inertia of the circulation becomes important in a
shallow subsurface boundary layer having a relative depth determined
by the approximate ratio of centrifugal to gravitational force, and by
the ratio of the free-fall time to the Kelvin-Helmholtz contraction
time. The structure equations appropriate to the boundary layer are
derived using stretched variable techniques, and qualitative features
of the flow discussed. There is found to be minimal deviation from
the Von Zeipel gravity darkening law through the boundary layer for
all rotation speeds.
---------------------------------------------------------
Title: Cosmological solutions of the mass integral formulation of
general relativity.
Authors: Roxburgh, I. W.
1977MNRAS.181..637R Altcode:
The cosmological solutions of general relativity give three isotropic
homogeneous cosmological models determined by the curvature of
three-space (k = 0, +1, -1). In the mass integral formulation of Hoyle
and Narlikar (1964), the differential form of the theory is identical
to general relativity but because of the integral form of the mass
field, these solutions must satisfy a self-consistency condition. By
mapping the k = -1 model into the uniformly expanding Milne model,
the mass integral is evaluated and shown to be self-consistent. Thus
this formulation of general relativity does not uniquely determine
the cosmological solution.
---------------------------------------------------------
Title: Large number hypothesis and continuous creation cosmologies
Authors: Roxburgh, I. W.
1977Natur.268..504R Altcode:
The large number hypothesis and the condition that general relativity is
satisfied in Einstein units, allows a family of cosmological models, two
of which are the Dirac model without creation and the more recent Dirac
model with multiplicative creation. The new models have multiplicative
creation, a cosmological scale factor S(t) ~ t<SUP>m</SUP>, and are
spatially flat; a multiplicative steady state model also satisfies
the hypotheses. How these models affect the temperature of the Earth
and the cosmological deceleration parameter is important.
---------------------------------------------------------
Title: The onset of microinstability and its consequences in the
solar wind
Authors: Singer, C. E.; Roxburgh, I. W.
1977JGR....82.2677S Altcode:
A simple and general method for applying the results of
a microinstability analysis to models of the solar wind is
described. Existing two-fluid models are found to become unstable
at heliocentric distances varying from 3 to 11 R<SUB>S</SUB>. The
development of these ‘heat conduction’ microinstabilities affects
the energy and momentum transport, observable wave spectrum, cosmic ray
diffusion, and properties of minor ions in the solar wind. A proposal
which would rationally modify the energy transport is developed. It is
suggested that the plasma fluctuations observed near the earth could
largely be a result of these instabilities. The observed temperatures
and velocities of helium ions can be explained qualitatively in terms
of resonant interaction with the different waves which are expected
to be generated under different solar wind conditions.
---------------------------------------------------------
Title: Christmas Lecture: Is the Universe Unique?
Authors: Roxburgh, I. W.
1977JBAA...87..341R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Testing Relativity and Gravitational Theories by Radar Ranging
to a Heliocentric Satellite
Authors: Roxburgh, I. W.
1977RSPTA.284..589R Altcode: 1977RSLPT.284..589R
Laser ranging to the Moon and radar ranging to the planets and
space probes are providing increasingly more accurate estimates of
post-Newtonian gravitational effects. This paper summarizes the results
obtained so far and outlines future possibilities of more accurate
tests of relativity by laser and X and K band ranging to space probes,
particularly to a highly eccentric or direct impact solar probe.
---------------------------------------------------------
Title: Testing Relativity and Gravitational Theories by Radar Ranging
to a Heliocentric Satellite: Discussion
Authors: Weightman, J. A.; Roxburgh, I. W.
1977RSPTA.284..593W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Nonlinear Lagrangian theories of gravity.
Authors: Roxburgh, Ian W.
1977GReGr...8..219R Altcode:
Gravitational theories derived from an action principle where the
Lagrange density is a power of the curvature scalerR <SUP> n </SUP>
are investigated. For all values ofn the theories have the correct
Newtonian limit and forn = 1 the same weak field solution, which
predicts a bending of light of three-quarters of the value predicted
by general relativity (n=1).
---------------------------------------------------------
Title: Dirac's continuous creation cosmology and the temperature of
the Earth (reply)
Authors: Roxburgh
1977Natur.265..763R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Theories of Gravitation and the Solar System
Authors: Roxburgh, I. W.
1977grep.conf..171R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar Interior
Authors: Durrant, C. J.; Roxburgh, I. W.
1977ASSL...69....1D Altcode: 1977igss.conf....1D
Solar Standard Model Internal Rotation Energy Generation Solar Neutrinos
Convection Zone Convective Theory Boussinesq Assumption
---------------------------------------------------------
Title: The stability of low mass contact binaries.
Authors: Williams, P. S.; Roxburgh, I. W.
1976MNRAS.176...81W Altcode:
The equilibrium of a low-mass contact binary system is investigated
by considering the stability of main-sequence components of 0.6 solar
mass to both mass loss and mass gain. A contact system of equal masses
is shown to be unstable to mass exchange on a dynamical time scale and
to evolve rapidly into a detached system with a mass ratio of 0.8. As
the system readjusts on a thermal time scale, it will either evolve
into a nearly-contact stable system with this mass ratio or oscillate
between two unstable nearly-contact states, spending most of the time
as a nearly-contact unequal-mass system.
---------------------------------------------------------
Title: Dirac's continuous creation cosmology and the temperature of
the Earth
Authors: Roxburgh, Ian W.
1976Natur.261..301R Altcode:
DIRAC<SUP>1,2</SUP> has modified his earlier cosmological model
based on the large number hypothesis<SUP>3,4</SUP>, that the observed
approximate equalities are not accidental but causal-even though we
are as yet unaware of the nature of the relationship between cosmology
and local physics (e is the electronic charge, G the gravitational
constant, c the velocity of light, ρ the mean density of the Universe,
H Hubble's constant and m an atomic mass). In the earlier version,
Dirac assumed mass conservation and that equalities (1) held for all
time, thus where R(t) is the cosmological scale factor, H = R/R. In the
modified version, Dirac argues (unconvincingly in my view) that R(t)
~ t, in which case that is, matter is continuously created such that
ρ<SUB>0</SUB> ~ t <SUP>2</SUP> where t is the age of the Universe. This
newly created matter could be produced uniformly throughout space, or
locally in proportion to the amount and composition of matter already
present. Dirac prefers the second alternative, but we shall show that
this leads to an unacceptable past temperature for the Earth.
---------------------------------------------------------
Title: The Internal Structure of the Sun and Solar Type Stars
Authors: Roxburgh, I. W.
1976IAUS...71..453R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Dogon tribe and Sirius
Authors: Roxburgh, I. W.; Williams, I. P.
1975Obs....95..215R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The gravitational theories of Poincaré and Milne and the
non-Riemannian kinematic models of the universe.
Authors: Roxburgh, I. W.; Tavakol, R.
1975MNRAS.170..599R Altcode:
Milne's general kinematic discussion on cosmological models is reviewed,
revised and extended and it is shown that Riemannian geometry is
insufficient for describing the general class of Milne's theories
and that these theories if they are to be geometrized need the more
general framework of Finsler spaces. Poincare's early relativistic
gravitational theory is then reviewed and applied to the one-body and
cosmological problems. It is shown that this theory is not Riemannian
geometrizable but is Finsler geometrizable. The cosmological solution
is explicitly evaluated and shown to be an example of Milne's general
kinematic models.
---------------------------------------------------------
Title: On the Effect of Latitude Dependent Base Conditions on the
Structure of the Solar Wind
Authors: Roxburgh, I. W.; Singer, C.
1975SoPh...41..241R Altcode:
The isothermal solar wind equations are solved for the case where the
coronal conditions vary with latitude. It is found that the solutions
are not uniquely determined by the base density but require knowledge
of the injection angle of the fluid. Even for the case of spherically
symmetric density at the corona, the solutions are not unique and form
a one parameter set, but the latitude variation decreases rapidly with
increasing heliocentric distance.
---------------------------------------------------------
Title: Solar neutrinos and solar rotation.
Authors: Roxburgh, I. W.
1975MNRAS.170P..35R Altcode:
Recent criticisms by Monaghan (1974) of suggestions that rapid rotation
lowers the neutrino flux from the sun are replied to and shown to
be invalid. Rapid differential rotation is capable of lowering the
neutrino flux provided the ratio of centrifugal force to gravity
decreases outwards in the sun.
---------------------------------------------------------
Title: The effect of rotation in stellar structure and evolution
Authors: Roxburgh, I. W.
1975MSRSL...8...15R Altcode: 1975phs..conf...15R
The development of our understanding of rotation in stellar structure
and evolution is briefly reviewed. More recent work on rotation and
convection, solar oblateness, the stability of differential rotation and
the effect of rapid rotation on the solar neutrino flux is discussed.
---------------------------------------------------------
Title: Splitting the stars.
Authors: Roxburgh, I. W.
1974JBAA...85....8R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Nature of the Asymptotically Adiabatic Solution of
the Two-Fluid Solar Wind
Authors: Roxburgh, Ian W.
1974ApJ...191..557R Altcode:
It is shown that there are the four degrees of freedom in the
asymptotically adiabatic solutions of the solarwind models. The electron
and proton temperatures tend to equality at large distances like T0r
-413, T0 being the same for both the electron and proton gases. For a
given T0 there exists another branch of solutions that converge on to
this in an asymptotically irregular manner like S0r1 '2 - 413) exp (-
r), where is a constant, known in terms of T0, and 5o represents the
extra degree of freedom required to specify arbitrarily the density and
electron and proton temperature at the Sun. Subject heading: solar wind
---------------------------------------------------------
Title: The masses of stable gas clouds
Authors: Roxburgh, I. W.; van der Reijden, W.
1974MmSAI..45..485R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The pre main sequence contraction of rapidly rotating stars
and equatorial mass loss
Authors: Roxburgh, I. W.; Williams, P. S.
1974MmSAI..45..477R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Note on Anisotropic Convection and the Rotation of Stellar
Convective Zones
Authors: Roxburgh, Ian W.
1974Ap&SS..27..419R Altcode:
The interaction of rotation and convection produces a latitude dependent
anisotropic turbulent viscosity. When this friction is dominant,
equilibrium of a convective outer layer of a star is achieved by an
equatorial acceleration and a two-zone circulation, towards the equator
at low surface latitudes.
---------------------------------------------------------
Title: A Note on the Solution of the Saturation Flux Limited Solar
Wind Equations
Authors: Roxburgh, Ian W.
1974SoPh...35..481R Altcode:
The solution curves of the differential equations determining the
behavior of the solar wind are calculated for the case where the heat
flux has its maximum value 3/2 nkTv<SUB>th</SUB>. All the supersonic
solutions are asymptotically adiabatic, T ∼r<SUP>-4/3</SUP>.
---------------------------------------------------------
Title: Non-Uniformly Rotating, Self-Gravitating, Compressible Masses
with Internal Meridian Circulation
Authors: Roxburgh, Ian W.
1974Ap&SS..27..425R Altcode:
The structure of self-gravitating, inviscid, compressible fluids
is investigated assuming a polytropic relation between pressure and
density. A class of solutions with non-uniform rotation and internal
meridian circulation are presented and the stream lines of the flow
calculated using a perturbation technique.
---------------------------------------------------------
Title: Internal rotation of the Sun and the solar neutrino flux
Authors: Roxburgh, Ian W.
1974Natur.248..209R Altcode:
THE low upper limit of 1 SNU (10<SUP>-36</SUP> captures per
<SUP>37</SUP>Cl atom s<SUP>-1</SUP>) on the observed neutrino flux from
the Sun obtained by Davis<SUP>1</SUP> has proved an embarrassment to
stellar physicists, and in spite of considerable intellectual gymnastics
the standard solar models predict at least 6 SNU (ref. 2). The
essential difficulty has been to produce a model with a low enough
central temperature that can still produce the observed luminosity of
the Sun with an age of 4.7 × 10<SUP>9</SUP> yr.
---------------------------------------------------------
Title: Solar oblateness and the solar quadrupole moment
Authors: Roxburgh, I. W.
1974exgr.conf..525R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Neutron stars.
Authors: Roxburgh, I. W.
1973PhB....24..664R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Asymptotic Behavior of the Supersonic Solutions of the
Two-Fluid Solar Wind Equations
Authors: Roxburgh, I. W.
1972SoPh...27..478R Altcode:
Three different asymptotic branches of the two-fluid equations are found
with τ<SUB>e</SUB>αλ<SUP>m</SUP>, τ<SUB>p</SUB>αλ<SUP>n</SUP>,
where, λ is the inverse distance from the Sun, with (m, n) = (2/7,
2/7), (2/7, 6/7), (4/3, 4/3); other special solutions are also found
but they correspond to special choices of density and temperature at
the corona. In all the (4/3, 4/3) solutions, the electron and proton
temperatures tend to equality at large distances.
---------------------------------------------------------
Title: Late supergiant evolution.
Authors: Roxburgh, I. W.; Williams, I. P.
1972css..conf..279R Altcode: 1971css..conf..279R
No abstract at ADS
---------------------------------------------------------
Title: Inhomogeneous convection and the equatorial acceleration of
the sun.
Authors: Durney, B. R.; Roxburgh, I. W.
1971BAAS....3S.260D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Inhomogeneous Convection and the Equatorial Acceleration of
the Sun
Authors: Durney, B. R.; Roxburgh, I. W.
1971SoPh...16....3D Altcode:
The interaction of rotation and turbulent convection is assumed to give
rise to an inhomogeneous, but isotropic, latitude dependent turbulent
energy transport, which is described by a `convective conduction
coefficient κ<SUB>c</SUB>' which varies with latitude. Energy
balance in the convective zone is then possible only with a slow
meridian circulation in the outer convective zone of the sun. The
angular momentum transported by this circulation is balanced in a
steady state by turbulent viscous transport down an angular velocity
gradient. A detailed model is constructed allowing for the transition
from convective transport to radiative transport at the boundaries
of the convective zone, by using a perturbation analysis in which the
latitude variation of κ<SUB>c</SUB> is small. The solution for a thin
compressible shell gives equatorial acceleration and a hotter equator
than pole, assuming that the convection is preferentially stabilised at
the equator. For agreement with the sun's equatorial acceleration the
model predicts an equatorial temperature excess of 70 K and a surface
meridional velocity of 350 cm/sec from pole to equator.
---------------------------------------------------------
Title: On the Equatorial Acceleration of the Sun
Authors: Roxburgh, I. W.
1970stro.coll..318R Altcode: 1970IAUCo...4..318R
No abstract at ADS
---------------------------------------------------------
Title: Models of close and contact binary stars 1.Polytropic models
Authors: Durney, B. R.; Roxburgh, I. W.
1970MNRAS.148..239D Altcode:
Polytropic models of close and contact binary stars are
constructed using a combination of perturbation techniques and
a Laplace approximation previously applied to uniformly rotating
stars. Synchronism between orbital and intrinsic angular velocity is
assumed. Models are constructed including the effects of distortion
for polytropes with indices fl = 1, , 2, 3 and 4. The conditions for
the two stars to be just in contact are determined and contact models
with a mass ratio of unity are constructed, right up to the limiting
case when the stars fill all the available space inside the critical
Roche surface surrounding the two stars. When the two stars are built
on the same polytropic model contact stars with mass ratios different
from unity are not possible.
---------------------------------------------------------
Title: Plasma physics in an astrophysical environment.
Authors: Roxburgh, I. W.
1969ppaa.book.....R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The oblateness of the Sun.
Authors: Roxburgh, I. W.
1969ampe.conf...29R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Pulsation Periods of Rotating White Dwarfs
Authors: Durney, B. R.; Faulkner, J.; Gribbin, J. R.; Roxburgh, I. W.
1968Natur.219...20D Altcode:
When uniform rotation is included, the periods of pulsation for
white dwarfs can become as small as 0.9 s. With non-uniform rotation,
periods as short as 0.1 s may be possible.
---------------------------------------------------------
Title: Uniformly Rotating Main-Sequence Stars
Authors: Faulkner, J.; Roxburgh, I. W.; Strittmatter, P. A.
1968ApJ...151..203F Altcode:
Models of homogeneous, uniformly rotating main-sequence stars
have been constructed by an ex- tension of the method described by
Roxburgh, Griffith, and Sweet and results for three stellar masses
are presented here Detailed opacity and nuclear energy generation
data were included and the prescription due to Faulkner, Griffiths,
and Hoyle was adopted to determine the surface boundary conditions. By
subsequently fitting appropriate "gray" atmospheres at each latitude
the changes in visual magnitude V and color index B - V were evaluated
for a range of rotational velocities and aspect angles At maxi- mum
rotational speed there are found to be differences of up to 1.3 mag in
V and 0.25 mag in B - V for stars of the same mass seen at different
orientation. The maximum spread in the main sequence ranges between
0.4 and 1.2 mag depending on color
---------------------------------------------------------
Title: The Origin and Early Evolution of Close Binary Stars
Authors: Roxburgh, I. W.
1968HiA.....1..451R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar Oblateness
Authors: Roxburgh, I. W.
1967Natur.216.1286R Altcode:
In this article the author answers criticism, by Dicke and Goldenberg,
on his theory of why the Sun is oblate.
---------------------------------------------------------
Title: On the densities of middle-aged stars
Authors: Faulkner, J.; Roxburgh, I. W.
1967Obs....87..171F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Origin of Planetary Nebulae
Authors: Roxburgh, Ian W.
1967Natur.215..838R Altcode:
STATISTICAL arguments have been advanced to demonstrate that all
or a large fraction of stars with masses comparable with that
of the Sun become planetary nebulae during the course of their
evolution<SUP>1,2</SUP>. It has further been argued that these stars
are the evolutionary products of horizontal branch stars, although
the mechanism for the ejection of the expanding shell has remained
a mystery.
---------------------------------------------------------
Title: Implications of the Oblateness of the Sun
Authors: Roxburgh, Ian W.
1967Natur.213.1077R Altcode:
Recent measurements of the oblateness of the Sun have been used to
determine its quadrupole moment and thus its effect on the perihelion
of Mercury. It is shown that these calculations could well be incorrect
and that the measured oblateness is that expected if the Sun is slowly
rotating throughout, since the surface is not one of constant potential.
---------------------------------------------------------
Title: The Structure and Stability of Rotating Massive Stars in
General Relativity
Authors: Roxburgh, I. W.
1967LIACo..14..131R Altcode: 1967MSRSL..15..131R; 1967LIACo...6..131R
No abstract at ADS
---------------------------------------------------------
Title: Effect of Rotation and Magnetic Fields on the Formation of
Single and Multiple Stars
Authors: Roxburgh, I. W.
1967LIACo..14..343R Altcode: 1967LIACo...6..343R; 1967MSRSL..15..343R
No abstract at ADS
---------------------------------------------------------
Title: Genesis of binaries (capture, accretion, scission, novae,
etc.): Effect of rotation and magnetic fields on the formation of
single and multiple stars
Authors: Roxburgh, I. W.
1967oeds.conf...60R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Rotation and Magnetism in Stellar Structure and Evolution
Authors: Roxburgh, Ian W.
1967mrs..conf...45R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Rotating Massive Stars in General Relativity
Authors: Durney, B. R.; Roxburgh, I. W.
1967RSPSA.296..189D Altcode:
Equilibrium models of uniformly rotating massive stars are investigated,
using a weak field, slow rotation approximation, which is shown to be
adequate for all cases of interest. The fate of radial perturbations
about these equilibrium configurations is investigated using a
linearized stability analysis to determine the oscillation frequency
σ in a peturbation propto e<SUP>1σ t</SUP>. An eigenvalue equation
for σ^2 is obtained which can be made self adjoint with respect to
the spatial metric, and a variational principle to determine σ^2 is
derived. Numerical determinations of σ^2 have been carried out for a
variety of masses, radii and rotational velocities, and these results
are incorporated in a simple formula that gives the dependence of σ^2
on these quantities. The condition for instability, σ^2 negative,
is determined, and it is found that for large masses and maximum
rotation velocity, so that when centrifugal force balances gravity at
the surface, a massive star becomes unstable when its radius is 208
times the Schwarzschild radius 2GM/c^2.
---------------------------------------------------------
Title: The effect of a toroidal magnetic field on the radial
oscillations of stars
Authors: Roxburgh, I. W.; Durney, B. R.
1967MNRAS.135..329R Altcode:
The internal structure of a polytrope n =3 containing a toroidal
magnetic field is investigated. For static equilibrium configurations
the general solution for the structure of the field is given and
a particular solution Ht rp sin 0 is investigated in detail. The
linearized equations for small radial motion about the equilibrium
configuration are presented and with a time dependence ei these
equations reduce to an eigenvalue equation for 2 A variational principle
for determiing is derived and 2 is estimated using this principle
as well as by direct numerical iteration, for values of the ratio of
specific heats of the gas F = 4/3,413+ , and 5/3. Results are given
for different field strengths. For F =4/3 the star is neutrally stable
whether or not there is a magnetic field, whereas for the other values
of F the magnetic field decreases the value of a as compared to the
non-magnetic values.
---------------------------------------------------------
Title: Decay of Stellar Magnetic Fields
Authors: Roxburgh, I. W.; Suffolk, G. C. J.
1967ZA.....66....1R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Determination of rotational velocity and aspect for stars
in clusters
Authors: Roxburgh, I. W.; Sargent, W. L. W.; Strittmatter, P. A.
1966Obs....86..118R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: KO Aquilae as an example of systems with undersize subgiant
secondaries in pre-main sequence contraction.
Authors: Roxburgh, I. W.
1966AJ.....71..133R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On stellar rotation, III. Thermally generated magnetic fields
Authors: Roxburgh, I. W.
1966MNRAS.132..201R Altcode:
The battery effect of the electron partial pressure must generate a
toroidal magnetic field in an initially non-magnetic rotating star,
since there is no steady state solution that gives the centrifugal force
curl free, whether or not there is maintained meridian circulation. The
magnitude of the thermally generated field is discussed and a detailed
calculation of the case with zero circulation is presented when the
limit on the growth of the field comes from Ohmic dissipation. Results
are presented for both the steady state, and the build up to the steady
state solution. The work presented here differs from previous work of
Biermaun and Schluter in that the solution is fully self-consistent,
both with the electro-dynamics and the conditions of dynamical and
thermal equilibrium.
---------------------------------------------------------
Title: Magnetostatic equilibrium of polytropes
Authors: Roxburgh, I. W.
1966MNRAS.132..347R Altcode:
The equilibrium structure of magnetic fields in stars is investigated
assuming the star to be a polytrope and the structure of the field is
determined for values of the polytropic index fl=0, I, , 2 and 3, using
a first order perturbation theory. As the magnetic body force becomes
vanishingly small in the surface layers this method is satisfactory. The
first three eigen solutions are determined and it is shown that whereas
for n I the number of nodes of the field increases with an increasing
ratio of toroidal to poloidal field strength, for n> I the field
has no nodes between centre and surface, for all values of this ratio.
---------------------------------------------------------
Title: On the Fission Theory of the Origin of Binary Stars
Authors: Roxburgh, Ian W.
1966ApJ...143..111R Altcode:
The pre-main-sequence evolution of a rotating non-magnetic star is
investigated. Stars forming out of interstellar gas clouds are shown to
have sufficient angular momentum to cause centrifugal force to balance
gravity before reaching the stable Hayashi phase, so that during
subsequent evolution matter must be left behind from the equatorial
regions. During contraction through the fully convective Hayasbi phase
the coupling of central and surface regions by convection determines
a definite rotation law which we take to be uniform rotation. YVith
continued contraction the star develops a radiative core and the
"viscosity" effect of the turbulence is no longer operative; each
element of the growing core therefore conserves its angular momentum
causing an inward increase in angular velocity. It is shown that
the ratio of centrifugal force to gravity increases in the central
regions and that for stars with mass > 0.8 Mo rotational instability
is likely to occur. This is imagined to cause the splitting of the
original star into two components and so form a binary system. Assuming
conservation of angular momentum on fission it is shown that stars
with mass 4 Mo can form a contact binary system whereas more massive
stars will produce separated binaries. The theoretical limits of Mo
and 4 Mo for the total mass of contact binanes are in good agreement
with observations of V Ursae ajoris systems, as is the distribution
of total angular momentum with mass.
---------------------------------------------------------
Title: Structure, Oscillations and Stability of Rotating White Dwarfs
Authors: Roxburgh, I. W.; Durney, B. R.
1966ZA.....64..504R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On steller rotation, V. The Structure of rotating stars
Authors: Roxburgh, I. W.; Strittmatter, P. A.
1966MNRAS.133..345R Altcode:
In previous papers in this series the structure of rotating, upper
main sequence stars was examined, and the distributions of angular
momentum and magnetic field strength were derived under the assumption
that there was no large scale meridional circulation. In this paper
we obtain the changes in the remaining physical quantities due to the
effect of rotation. Results are given for models with Schwarzschild,
Kramers and electron scattering opacity laws and, in the latter case,
for a series of values of magnetic field strength. The change in the
position of a star in a plot of Mbol v. log Te is given in terms of the
parameter A - c2R u3/GM both for stars viewed pole on and perpendicular
to the rotation axis. ( c' the angular velocity of the convective core,
Ru the radius of a non-rotating star of mass M.) It is shown that the
total luminosity of a star is reduced by rotation but that at a given
value of Te rotating stars appear brighter than their non-rotating
counterparts.
---------------------------------------------------------
Title: On stellar rotation. IV, Thermally generated magnetic fields
limited by the Hall field
Authors: Roxburgh, I. W.; Strittmatter, P. A.
1966MNRAS.133....1R Altcode:
The analysis of previous papers is extended to consider the structure
of the rotation and magnetic fields inside non-uniformly rotating early
main sequence stars, where the limit on the growth of the thermally
generated toroidal magnetic field comes from the Hall effect than
rather the olimic field. Assuming a steady state with vanishing
circulation currents the structure and electrodynamic equations are
solved simultaneously using a first order perturbation analysis. The
solutions obtained depend on the assumpt&.on regarding the structure
of magnetic fields in convective zones, but all give an outward
increase in angular velocity, in contrast to the solutions derived in
Papers I and II of this series. If, as is usual, we assume that there
is no large scale component of magnetic field in the convective core,
then the angular velocity at the surface is I o86 times the value in
the central convective core. The magnetic field has a maximum at of
the radius of x 107A1I2MR-2 Gauss where A is the ratio of centrifugal
force to gravity at the surface of the star. This gives a field of 3
X 100 Gauss in a typical rapidly rotating 0 or B star.
---------------------------------------------------------
Title: Stability of Rotating Massive Stars in General Relativity
Authors: Durney, B.; Roxburgh, I. W.
1965Natur.208.1304D Altcode:
THE suggestion by Hoyle and Fowler<SUP>1</SUP> that stars with masses
of 10<SUP>6</SUP>-10<SUP>10</SUP> M<SUB>solar</SUB> may provide the
energy for radio sources, and the subsequent discovery of quasars,
has stimulated considerable interest in the structure of very massive
stars<SUP>2</SUP>. Iben<SUP>3</SUP>, using a binding-energy argument,
showed that within the framework of general relativity a spherical
massive star becomes unstable long before it has contracted to
the stage at which nuclear reactions become important. A similar
conclusion was obtained by Chandrasekhar<SUP>4</SUP>, using a detailed
stability analysis on the spherically symmetric relativistic equations
and calculating the relaxation oscillations from a variational
principle. Similar results have been obtained by Fowler<SUP>5</SUP>
using a virial theorem approach.
---------------------------------------------------------
Title: KO Aquilae as an Example of Close Binary Systems with Undersize
Subgiant Secondaries in Pre-Main Sequence Contraction.
Authors: Roxburgh, Ian W.
1965AJ.....70..690R Altcode:
The hypothesis is advanced that close binary systems with an undersize
subgiant secondary are in the pre-main sequence evolutionary phase,
and applied to the system KO Aquilae. Since KO Aquilae is a single
spectrum binary a complete description of the system can be obtained by
supposing that the primary is contracting towards the main sequence,
and the age of the system is found to be 3.5 x 1013 sec, the mass
of the primary 2.9M0. and the secondary 0.58Mo.. The radius of the
primary is found to be 2.6R0. and that of the secondary 2.lR0.,
while the distance between the mass centers is 13R0.. To confirm
our hypothesis we compute the radius of a star of 0.58M0 after 3.5 x
1013 sec and this is found to lie between 1.9Ro. and 2.3Ra., in good
agreement with the previous determination. The angular momentum of the
system is computed and is found to be in satisfactory agreement with
the predictions of the fission theory as advanced by Roxburgh (1965).
---------------------------------------------------------
Title: Effect of Rotation on the Stability of Very Massive Stars
Authors: Roxburgh, Ian W.
1965Natur.207..363R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Fission Theory of the Origin of Binary Stars.
Authors: Roxburgh, Ian W.
1965AJ.....70..330R Altcode:
The pre-main sequence evolution of a rotating nonmagnetic star
is investigated and it is found that rotational instability will
occur in the central regions of the star during the development of
a radiative core, provided that the total mass exceeds 0.8M0.. This
is imagined to give rise to the splitting of the central regions
and the formation of a binary system. A discussion of the angular
momentum of the objects predicts that for a total mass between 0.8M0
and 4.0M0. the end product should be a contact configuration of the W
Ursae Majoris type. For larger masses the star must form a separated
binary system. The predicted distribution of angular momentum with
mass is in good agreement with observations of W Ursae Majoris systems.
---------------------------------------------------------
Title: Solar rotation and the perihelion advance of the planets a
reply to comments by G.M. Clemence on the paper by I.W. Roxburgh
Authors: Roxburgh, Ian W.
1965Icar....4..220R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Rotational Spread of the Main Sequence
Authors: Roxburgh, I. W.; Strittmatter, P. A.
1965ZA.....63...15R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A note on the boundary of convective zones in stars
Authors: Roxburgh, Ian W.
1965MNRAS.130..223R Altcode:
Convective motions overshoot the boundary of convective zones in stellar
models, producing an extended convective zone. This overshooting
is considered and the radius of the extended zone is evaluated. The
importance of this overshooting for the theory of stellar rotation
is discussed.
---------------------------------------------------------
Title: The growth of condensations in a Newtonian model of the steady
state universe
Authors: Roxburgh, I. W.; Saffman, P. G.
1965MNRAS.129..181R Altcode:
A Newtonian model of the cold steady-state universe is proposed
in which new material is created with the same velocity as its
surroundings, and the stability of such a universe is examined. If
K= 47T/3 Gp0 H- 2is greater than 2 the universe is unstable against
small disturbances; if K is less than 2 the universe is stable against
regular small disturbances, but it is shown that there still exist
non-regular disturbances for which the universe is unstable. An
exact similarity solution of the equations governing the growth of
a spherically symmetric condensation is given for the case K< 2,
and the condensation is found to grow like e3aHt, where 2oL = (I +4K)
- I. The ondition that the universe be self-propagating gives the
relation - 1+'1 for the number density N of condensations with mass M.
---------------------------------------------------------
Title: The structure of rapidly rotating polytropes
Authors: Monaghan, J. J.; Roxburgh, I. W.
1965MNRAS.131...13M Altcode:
The structure of rapidiy rotating polytropes is investigated using
an approximation technique of integrating outwards from the centre
and inwards from the surface, matching the two solutions at an
interface. Results are presented for values of the polytropic index fl=
I, , 2, , 3, , 4. The method used is an extension of Jeans' generalized
Roche model.
---------------------------------------------------------
Title: On Models of Non Spherical Stars I. The Theory of Rapildy
Rotating Main Sequence Stars. With 3 Figures in the Text
Authors: Roxburgh, I. W.; Griffith, J. S.; Sweet, P. A.
1965ZA.....61..203R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On Models of Non Spherical Stars. II. Rotating White
Dwarfs. With 2 Figures in the Text
Authors: Roxburgh, I. W.
1965ZA.....62..134R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Some steady, self-consistent solutions for rotating magnetic
stars
Authors: Roxburgh, I. W.
1965IAUS...22..103R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar Rotation and the Perihelion Advance of the Planets
Authors: Roxburgh, Ian W.
1964Icar....3...92R Altcode:
The hypothesis that the inside of the Sun is rotating much more rapidly
than the surface layers is examined and found to be consistent with
present ideas on the formation of the solar system and the internal
constitution of the Sun. The angular velocity of the inner region
is estimated and it is shown that the rotational distortion of the
Sun produces a perihelion advance of the planets. If the angular
velocity inside the Sun has the same magnitude as in a typical rapidly
rotating star, then the anomalous advance of the perihelion of Mercury,
usually counted as one of the crucial tests of general relativity,
can be explained by the gravitational effect of the rotating Sun.
---------------------------------------------------------
Title: On stellar rotation, I. The rotation of upper main-sequence
stars
Authors: Roxburgh, I. W.
1964MNRAS.128..157R Altcode:
The centrifugal perturbation to the thermal field drives meridional
circulation in radiative zones of rotating stars. Transport of
angnlar momentum by the circulation changes the angnlar velocity
field and hence the circulation itself. We here assume that the system
approaches a steady state in which there is no meridional circulation,
and calculate that distribution of angnlar velocity that does not
upset radiative equllibrium, assuming that the star has no internal
magnetic field. Results are obtained for two upper main-sequence
stellar models: one with the opacity given by a modified Kramer's law,
the other with electron scattering. The angnlar velocity is found to
be a monotonically decreasing function of distance from the centre of
the star and to be independent of latitude, so that the star rotates
in spherical shells. The solution is shown to be dynamically stable.
---------------------------------------------------------
Title: On stellar rotation, II. The rotation of lower main-sequence
stars
Authors: Roxburgh, I. W.
1964MNRAS.128..237R Altcode:
The first-order perturbation analysis developed in Paper I is extended
to stars with a radiative core and convective envelope and with the
proton-proton chain as the source of energy. The variation of angnlar
velocity with distance from the centre of the star is calculated for
a model of the Sun in its initial main-sequence state. The inward
increase in angnlar velocity is too small to alter significantly the
value of the star's angnlar momentum computed under the assumption of
uniform rotation.
---------------------------------------------------------
Title: Stellar hydromagnetics
Authors: Roxburgh, I. W.
1963stev.conf..446R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Steady meridian circulation in rotating magnetic stars
Authors: Roxburgh, I. W.
1963MNRAS.126...67R Altcode:
It is well-known that non-spherical perturbations such as centrifugal
and magnetic forces lead, in general, to a thermally-driven meridian
circulation in stellar radiative zones. A circulation fast enough to
be of interest tends to distort the perturbation field that drives
it. In this paper we suppose that a steady state has been reached,
and study those rotation and magnetic fields that are unaffected by
the circulation field they generate. Only two cases are easy to treat:
one with the centrifugal force the dominant perturbation, and nearly
uniform rotation maintained by a weak poloidal magnetic field; the
other with the toroidal component of the magnetic field dominant.
---------------------------------------------------------
Title: On the Thermal Generation of Toroidal Magnetic Fields in
Rotating Stars.
Authors: Mestel, L.; Roxburgh, I. W.
1962ApJ...136..615M Altcode:
Biermann (1950) has shown that in a rotating star without any initial
magnetic field the electron partial pressure slowly generates a
toroidal magnetic field of considerable strength. The problem is
here reconsidered, assuming the star to have a primeval magnetic
field, with its poloidal component very much weaker than the toroidal
field predicted by Biermann. It is shown that the interaction of the
magnetic torque and the rotation field is sufficient to insure that
the electron pressure has negligible effect, whether or not there is
meridian circulation of matter inside the star.
