explanation blue bibcodes open ADS page with paths to full text
Author name code: unruh
ADS astronomy entries on 2022-09-14
author:"Unruh, Yvonne"
---------------------------------------------------------
Title: Making the Most of Transmission Spectra in Light of Stellar
Activity: Needs Identified by ExoPAG's Study Analysis Group 21
Authors: Rackham, Benjamin V.; Espinoza, Néstor; Berdyugina, Svetlana
V.; Korhonen, Heidi; MacDonald, Ryan J.; Montet, Benjamin T.; Morris,
Brett M.; Oshagh, Mahmoudreza; Shapiro, Alexander I.; Unruh, Yvonne
C.; Quintana, Elisa V.; Zellem, Robert T.; SAG 21 Committee
2022BAAS...54e4404R Altcode:
Transmission spectroscopy, a method for studying exoplanetary
atmospheres by measuring the wavelength-dependent radius of a planet as
it transits its star, relies on a precise understanding of the spectrum
of the star being occulted. However, stars are not homogeneous,
constant light sources but have temporally evolving photospheres
and chromospheres with inhomogeneities like spots, faculae, and
plages. Study Analysis Group 21 (SAG21) of NASA's Exoplanet Exploration
Program Analysis Group (ExoPAG) was organized to study the effect
of stellar photospheric heterogeneity on space-based transmission
spectroscopy. This SAG brought together an interdisciplinary team
of more than 100 scientists, with observers and theorists from the
heliophysics, stellar astrophysics, planetary science, and exoplanetary
atmosphere research communities, to study the current needs that can be
addressed in this context to make the most of transit studies from NASA
facilities like HST and JWST. Here we report on the main conclusions
of this analysis, highlighting needs to be addressed and mitigation
efforts underway. The analysis produced 14 findings, which fall into
three Science Themes that encompass (1) how the Sun is used as our best
laboratory to calibrate our understanding of stellar heterogeneities
("The Sun as the Stellar Benchmark"), (2) how stars other than the Sun
extend our knowledge of heterogeneities ("Surface Heterogeneities of
Other Stars"), and (3) how to incorporate information gathered for the
Sun and other stars into transit studies ("Mapping Stellar Knowledge
to Transit Studies"). Addressing the needs identified through this
large community effort will ensure that we can optimally leverage
space-based transmission spectra in light of stellar activity.
---------------------------------------------------------
Title: Energy deposition in Saturn's equatorial upper atmosphere
Authors: Chadney, J. M.; Koskinen, T. T.; Hu, X.; Galand, M.; Lavvas,
P.; Unruh, Y. C.; Serigano, J.; Hörst, S. M.; Yelle, R. V.
2022Icar..37214724C Altcode: 2021arXiv211008014C
We construct Saturn equatorial neutral temperature and density profiles
of H, H<SUB>2</SUB>, He, and CH<SUB>4</SUB>, between 10<SUP>-12</SUP>
and 1 bar using measurements from Cassini's Ion Neutral Mass
Spectrometer (INMS) taken during the spacecraft's final plunge into
Saturn's atmosphere on 15 September 2017, combined with previous
deeper atmospheric measurements from the Cassini Composite InfraRed
Spectrometer (CIRS) and from the UltraViolet Imaging Spectrograph
(UVIS). These neutral profiles are fed into an energy deposition
model employing soft X-ray and Extreme UltraViolet (EUV) solar fluxes
at a range of spectral resolutions (Δλ = 4 × 10<SUP>-3</SUP> nm
to 1 nm) assembled from TIMED/SEE, from SOHO/SUMER, and from the
Whole Heliosphere Interval (WHI) quiet Sun campaign. Our energy
deposition model calculates ion production rate profiles through
photo-ionisation and electron-impact ionisation processes, as well as
rates of photo-dissociation of CH<SUB>4</SUB>. The ion reaction rate
profiles we determine are important to obtain accurate ion density
profiles, meanwhile methane photo-dissociation is key to initiate
complex organic chemical processes. We assess the importance of spectral
resolution in the energy deposition model by using a high-resolution
H<SUB>2</SUB> photo-absorption cross section, which has the effect of
producing additional ionisation peaks near 800 km altitude. We find
that these peaks are still formed when using low-resolution (Δλ =
1 nm) or mid-resolution (Δλ = 0 . 1 nm) solar spectra, as long as
high-resolution cross sections are included in the model.
---------------------------------------------------------
Title: Final Report for SAG 21: The Effect of Stellar Contamination
on Space-based Transmission Spectroscopy
Authors: Rackham, Benjamin V.; Espinoza, Néstor; Berdyugina, Svetlana
V.; Korhonen, Heidi; MacDonald, Ryan J.; Montet, Benjamin T.; Morris,
Brett M.; Oshagh, Mahmoudreza; Shapiro, Alexander I.; Unruh, Yvonne C.;
Quintana, Elisa V.; Zellem, Robert T.; Apai, Dániel; Barclay, Thomas;
Barstow, Joanna K.; Bruno, Giovanni; Carone, Ludmila; Casewell, Sarah
L.; Cegla, Heather M.; Criscuoli, Serena; Fischer, Catherine; Fournier,
Damien; Giampapa, Mark S.; Giles, Helen; Iyer, Aishwarya; Kopp, Greg;
Kostogryz, Nadiia M.; Krivova, Natalie; Mallonn, Matthias; McGruder,
Chima; Molaverdikhani, Karan; Newton, Elisabeth R.; Panja, Mayukh;
Peacock, Sarah; Reardon, Kevin; Roettenbacher, Rachael M.; Scandariato,
Gaetano; Solanki, Sami; Stassun, Keivan G.; Steiner, Oskar; Stevenson,
Kevin B.; Tregloan-Reed, Jeremy; Valio, Adriana; Wedemeyer, Sven;
Welbanks, Luis; Yu, Jie; Alam, Munazza K.; Davenport, James R. A.;
Deming, Drake; Dong, Chuanfei; Ducrot, Elsa; Fisher, Chloe; Gilbert,
Emily; Kostov, Veselin; López-Morales, Mercedes; Line, Mike; Močnik,
Teo; Mullally, Susan; Paudel, Rishi R.; Ribas, Ignasi; Valenti, Jeff A.
2022arXiv220109905R Altcode:
Study Analysis Group 21 (SAG21) of the Exoplanet Exploration Program
Analysis Group (ExoPAG) was organized to study the effect of stellar
contamination on space-based transmission spectroscopy, a method for
studying exoplanetary atmospheres by measuring the wavelength-dependent
radius of a planet as it transits its star. Transmission spectroscopy
relies on a precise understanding of the spectrum of the star being
occulted. However, stars are not homogeneous, constant light sources
but have temporally evolving photospheres and chromospheres with
inhomogeneities like spots, faculae, and plages. This SAG has brought
together an interdisciplinary team of more than 100 scientists, with
observers and theorists from the heliophysics, stellar astrophysics,
planetary science, and exoplanetary atmosphere research communities,
to study the current needs that can be addressed in this context to
make the most of transit studies from current NASA facilities like
HST and JWST. The analysis produced 14 findings, which fall into
three Science Themes encompassing (1) how the Sun is used as our best
laboratory to calibrate our understanding of stellar heterogeneities
("The Sun as the Stellar Benchmark"), (2) how stars other than the Sun
extend our knowledge of heterogeneities ("Surface Heterogeneities of
Other Stars") and (3) how to incorporate information gathered for the
Sun and other stars into transit studies ("Mapping Stellar Knowledge
to Transit Studies").
---------------------------------------------------------
Title: MPS-ATLAS: A fast all-in-one code for synthesising stellar
spectra
Authors: Witzke, V.; Shapiro, A. I.; Cernetic, M.; Tagirov, R. V.;
Kostogryz, N. M.; Anusha, L. S.; Unruh, Y. C.; Solanki, S. K.; Kurucz,
R. L.
2021A&A...653A..65W Altcode: 2021arXiv210513611W
Context. Stellar spectral synthesis is essential for various
applications, ranging from determining stellar parameters to
comprehensive stellar variability calculations. New observational
resources as well as advanced stellar atmosphere modelling, taking three
dimensional effects from radiative magnetohydrodynamics calculations
into account, require a more efficient radiative transfer. <BR /> Aims:
For accurate, fast and flexible calculations of opacity distribution
functions (ODFs), stellar atmospheres, and stellar spectra, we developed
an efficient code building on the well-established ATLAS9 code. The new
code also paves the way for easy and fast access to different elemental
compositions in stellar calculations. <BR /> Methods: For the generation
of ODF tables, we further developed the well-established DFSYNTHE code
by implementing additional functionality and a speed-up by employing
a parallel computation scheme. In addition, the line lists used can be
changed from Kurucz's recent lists. In particular, we implemented the
VALD3 line list. <BR /> Results: A new code, the Merged Parallelised
Simplified ATLAS, is presented. It combines the efficient generation of
ODF, atmosphere modelling, and spectral synthesis in local thermodynamic
equilibrium, therefore being an all-in-one code. This all-in-one code
provides more numerical functionality and is substantially faster
compared to other available codes. The fully portable MPS-ATLAS code
is validated against previous ATLAS9 calculations, the PHOENIX code
calculations, and high-quality observations.
---------------------------------------------------------
Title: Forward modelling of Kepler-band variability due to faculae
and spots
Authors: Johnson, Luke J.; Norris, Charlotte M.; Unruh, Yvonne C.;
Solanki, Sami K.; Krivova, Natalie; Witzke, Veronika; Shapiro,
Alexander I.
2021MNRAS.504.4751J Altcode: 2021arXiv210411544J; 2021MNRAS.tmp.1190J
Variability observed in photometric light curves of late-type stars (on
time-scales longer than a day) is a dominant noise source in exoplanet
surveys and results predominantly from surface manifestations of stellar
magnetic activity, namely faculae and spots. The implementation of
faculae in light-curve models is an open problem, with scaling typically
based on spectra equivalent to hot stellar atmospheres or assuming a
solar-derived facular contrast. We modelled rotational (single period)
light curves of active G2, K0, M0, and M2 stars, with Sun-like surface
distributions and realistic limb-dependent contrasts for faculae and
spots. The sensitivity of light-curve variability to changes in model
parameters such as stellar inclination, feature area coverage, spot
temperature, facular region magnetic flux density, and active band
latitudes is explored. For our light-curve modelling approach we used
ACTRESS, a geometrically accurate model for stellar variability. ACTRESS
generates two-sphere maps representing stellar surfaces and populates
them with user-prescribed spot and facular region distributions. From
this, light curves can be calculated at any inclination. Quiet star limb
darkening and limb-dependent facular contrasts were derived from MURaM
3D magnetoconvection simulations using ATLAS9. 1D stellar atmosphere
models were used for the spot contrasts. We applied ACTRESS in Monte
Carlo simulations, calculating light-curve variability amplitudes in
the Kepler band. We found that, for a given spectral type and stellar
inclination, spot temperature and spot area coverage have the largest
effect on variability of all simulation parameters. For a spot coverage
of $1{{\ \rm per\ cent}}$, the typical variability of a solar-type
star is around 2 parts per thousand. The presence of faculae clearly
affects the mean brightness and light-curve shape, but has relatively
little influence on the variability.
---------------------------------------------------------
Title: Simulating Variability due to Faculae and Spots on GKM Stars
Authors: Johnson, Luke; Unruh, Yvonne; Norris, Charlotte; Solanki,
Sami; Krivova, Natalie; Witzke, Veronika; Shapiro, Alexander
2020EPSC...14..844J Altcode:
Stellar variability is a dominant noise source in exoplanet surveys
and results largely from the presence of photospheric faculae and
spots. The implementation of faculae in lightcurve models is an open
problem, with scaling based on spectra equivalent to hot stellar
atmospheres or assuming a solar-derived facular contrast. We model the
lightcurves of active late-type stars as they rotate, using emergent
intensity spectra calculated from 3D magnetoconvection simulations
of G, K and M-type stellar atmosphere regions at different viewing
angles to reproduce centre-to-limb brightness variations. We present
mean expected variability levels for several cases and compare with
solar and stellar observations. We also investigate the wavelength
dependence of variability. Fig. 1: Example of our geometrically
accurate lightcurve modelling approach. Top: normalised intensity
maps of a limb darkened, solar-type star viewed in the \textit{Kepler}
band at rotational phase 0.5 with stellar inclinations 90 deg (left)
and 30 deg (right). At 90 deg, the star is viewed equator-on. Middle:
Corresponding lightcurves calculated at inclinations 90 deg (black line)
and 30 deg (red line). Bottom: HealPix map representing the active
stellar surface, cosine-scaled in latitude and flattened in longitude
to resemble a solar synoptic map. The quiet photosphere is displayed
in orange, facular regions are bright yellow and spot regions are dark
blue. The crosses represent the centres of the stellar discs in the
top panel. Fig. 2: Example showing simulated lightcurves calculated
at different wavelengths. Rotational lightcurves are on the left,
transit lightcurves on the right. In the centre, one hemisphere of the
simulated stellar surface is shown, with a quarter of the disc shown
in each wavelength band. 'Giant' spots and facular regions are used
in this example. The transit path is highlighted in grey.
---------------------------------------------------------
Title: Connecting measurements of solar and stellar brightness
variations
Authors: Nèmec, N. -E.; Işık, E.; Shapiro, A. I.; Solanki, S. K.;
Krivova, N. A.; Unruh, Y.
2020A&A...638A..56N Altcode: 2020arXiv200406974N
Context. A comparison of solar and stellar brightness variations is
hampered by the difference in spectral passbands that are used in
observations, and also by the possible difference in the inclination
of the solar and stellar rotation axes from the line of sight. <BR />
Aims: We calculate the rotational variability of the Sun as it would
be measured in passbands used for stellar observations. In particular,
we consider the filter systems used by the CoRoT, Kepler, TESS, and
Gaia space missions. We also quantify the effect of the inclination
of the rotation axis on the solar rotational variability. <BR />
Methods: We employed the spectral and total irradiance reconstruction
(SATIRE) model to calculate solar brightness variations in different
filter systems as observed from the ecliptic plane. We then combined
the simulations of the surface distribution of the magnetic features
at different inclinations using a surface flux transport model with
the SATIRE calculations to compute the dependence of the variability
on the inclination. <BR /> Results: For an ecliptic-bound observer,
the amplitude of the solar rotational variability, as observed in
the total solar irradiance (TSI), is 0.68 mmag (averaged over solar
cycles 21-24). We obtained corresponding amplitudes in the Kepler
(0.74 mmag), CoRoT (0.73 mmag), TESS (0.62 mmag), Gaia G (0.74 mmag),
Gaia G<SUB>RP</SUB> (0.62 mmag), and Gaia G<SUB>BP</SUB> (0.86 mmag)
passbands. Decreasing the inclination of the rotation axis decreases
the rotational variability. For a sample of randomly inclined stars,
the variability is on average 15% lower in all filter systems we
considered. This almost compensates for the difference in amplitudes
of the variability in TSI and Kepler passbands, making the amplitudes
derived from the TSI records an ideal representation of the solar
rotational variability for comparison to Kepler stars with unknown
inclinations. <BR /> Conclusions: The TSI appears to be a relatively
good measure of solar variability for comparisons with stellar
measurements in the CoRoT, Kepler, TESS Gaia G, and Gaia G<SUB>RP</SUB>
filters. Whereas the correction factors can be used to convert the
variability amplitude from solar measurements into the values expected
for stellar missions, the inclination affects the shapes of the light
curves so that a much more sophisticated correction than simple scaling
is needed to obtain light curves out of the ecliptic for the Sun.
---------------------------------------------------------
Title: IGAPS: the merged IPHAS and UVEX optical surveys of the
northern Galactic plane
Authors: Monguió, M.; Greimel, R.; Drew, J. E.; Barentsen, G.;
Groot, P. J.; Irwin, M. J.; Casares, J.; Gänsicke, B. T.; Carter,
P. J.; Corral-Santana, J. M.; Gentile-Fusillo, N. P.; Greiss, S.; van
Haaften, L. M.; Hollands, M.; Jones, D.; Kupfer, T.; Manser, C. J.;
Murphy, D. N. A.; McLeod, A. F.; Oosting, T.; Parker, Q. A.; Pyrzas,
S.; Rodríguez-Gil, P.; van Roestel, J.; Scaringi, S.; Schellart, P.;
Toloza, O.; Vaduvescu, O.; van Spaandonk, L.; Verbeek, K.; Wright,
N. J.; Eislöffel, J.; Fabregat, J.; Harris, A.; Morris, R. A. H.;
Phillipps, S.; Raddi, R.; Sabin, L.; Unruh, Y.; Vink, J. S.; Wesson,
R.; Cardwell, A.; de Burgos, A.; Cochrane, R. K.; Doostmohammadi,
S.; Mocnik, T.; Stoev, H.; Suárez-Andrés, L.; Tudor, V.; Wilson,
T. G.; Zegmott, T. J.
2020A&A...638A..18M Altcode: 2020arXiv200205157M
The INT Galactic Plane Survey (IGAPS) is the merger of the optical
photometric surveys, IPHAS and UVEX, based on data from the Isaac
Newton Telescope (INT) obtained between 2003 and 2018. Here, we
present the IGAPS point source catalogue. It contains 295.4 million
rows providing photometry in the filters, i, r, narrow-band Hα,
g, and U<SUB>RGO</SUB>. The IGAPS footprint fills the Galactic
coordinate range, |b| < 5° and 30° < ℓ < 215°. A
uniform calibration, referred to as the Pan-STARRS system, is
applied to g, r, and i, while the Hα calibration is linked to r
and then is reconciled via field overlaps. The astrometry in all
five bands has been recalculated in the reference frame of Gaia Data
Release 2. Down to i ∼ 20 mag (Vega system), most stars are also
detected in g, r, and Hα. As exposures in the r band were obtained
in both the IPHAS and UVEX surveys, typically a few years apart,
the catalogue includes two distinct r measures, r<SUB>I</SUB> and
r<SUB>U</SUB>. The r 10σ limiting magnitude is approximately 21,
with median seeing of 1.1 arcsec. Between approximately 13th and 19th
mag in all bands, the photometry is internally reproducible to within
0.02 mag. Stars brighter than r = 19.5 mag are tested for narrow-band
Hα excess signalling line emission, and for variation exceeding
|r<SUB>I</SUB> - r<SUB>U</SUB>| = 0.2 mag. We find and flag 8292
candidate emission line stars and over 53 000 variables (both at >
5σ confidence). <P />The catalogue of 174 columns in total and full
Tables D.1-D.4 are only available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A>ftp://130.79.128.5)
or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/638/A18">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/638/A18</A>
---------------------------------------------------------
Title: VizieR Online Data Catalog: IGAPS. merged IPHAS and UVEX of
northern Galactic plane (Monguio+, 2020)
Authors: Monguio, M.; Greimel, R.; Drew, J. E.; Barentsen, G.;
Groot, P. J.; Irwin, M. J.; Casares, J.; Gaensicke, B. T.; Carter,
P. J.; Corral-Santana, J. M.; Gentile-Fusillo, N. P.; Greiss, S.; van
Haaften, L. M.; Hollands, M.; Jones, D.; Kupfer, T.; Manser, C. J.;
Murphy, D. N. A.; McLeod, A. F.; Oosting, T.; Parker, Q. A.; Pyrzas,
S.; Rodriguez-Gil, P.; van Roestel, J.; Scaringi, S.; Schellart, P.;
Toloza, O.; Vaduvescu, O.; van Spaandonk, L.; Verbeek, K.; Wright,
N. J.; Eisloeel, J.; Fabregat, J.; Harris, A.; Morris, R. A. H.;
Phillipps, S.; Raddi, R.; Sabin, L.; Unruh, Y.; S Vink, J.; Wesson,
R.; Cardwell, A.; de Burgos, A.; Cochrane, R. K.; Doostmohammadi, S.;
Mocnik, T.; Stoev, H.; Suarez-Andres, L.; Tudor, V.; Wilson, T. G.;
Zegmott, T. J.
2020yCat.5165....0M Altcode:
The INT Galactic Plane Survey (IGAPS) was formed from merging the
IPHAS (Drew et al., 2005MNRAS.362..753D) and UVEX (Groot et al.,
2009MNRAS.399..323G, Cat. J/MNRAS/399/323) surveys of the northern
Galactic plane, based on data from the Isaac Newton Telescope (INT)
obtained between 2003 and 2018. It is a catalogue of 174 columns and
almost 300 million rows, spanning the r magnitude range from 12-13th
mag down to 21st mag (10σ). The astrometry in all five photometric
bands has been placed in the Gaia DR2 reference frame. Broadband g,
r, and i have been uniformly calibrated using PanSTARRS data resting
on that project's 'Ubercal' (Magnier et al. 2013ApJS..205...20M). We
estimate the reproducibility of the photometry in these bands (and in
Hα) to be in the region of 0.02mag at magnitudes brighter than 19th
mag. <P />(1 data file).
---------------------------------------------------------
Title: Readdressing the UV solar variability with SATIRE-S: non-LTE
effects
Authors: Tagirov, R. V.; Shapiro, A. I.; Krivova, N. A.; Unruh, Y. C.;
Yeo, K. L.; Solanki, S. K.
2019A&A...631A.178T Altcode: 2019arXiv190911736T
Context. Solar spectral irradiance (SSI) variability is one of the key
inputs to models of the Earth's climate. Understanding solar irradiance
fluctuations also helps to place the Sun among other stars in terms of
their brightness variability patterns and to set detectability limits
for terrestrial exoplanets. <BR /> Aims: One of the most successful
and widely used models of solar irradiance variability is Spectral
And Total Irradiance REconstruction model (SATIRE-S). It uses spectra
of the magnetic features and surrounding quiet Sun that are computed
with the ATLAS9 spectral synthesis code under the assumption of local
thermodynamic equilibrium (LTE). SATIRE-S has been at the forefront
of solar variability modelling, but due to the limitations of the LTE
approximation its output SSI has to be empirically corrected below
300 nm, which reduces the physical consistency of its results. This
shortcoming is addressed in the present paper. <BR /> Methods: We
replaced the ATLAS9 spectra of all atmospheric components in SATIRE-S
with spectra that were calculated using the Non-LTE Spectral SYnthesis
(NESSY) code. To compute the spectrum of the quiet Sun and faculae,
we used the temperature and density stratification models of the FAL
set. <BR /> Results: We computed non-LTE contrasts of spots and faculae
and combined them with the corresponding fractional disc coverages,
or filling factors, to calculate the total and spectral irradiance
variability during solar cycle 24. The filling factors have been derived
from solar full-disc magnetograms and continuum images recorded by
the Helioseismic and Magnetic Imager on Solar Dynamics Observatory
(SDO/HMI). <BR /> Conclusions: The non-LTE contrasts yield total and
spectral solar irradiance variations that are in good agreement with
empirically corrected LTE irradiance calculations. This shows that
the empirical correction applied to the SATIRE-S total and spectral
solar irradiance is consistent with results from non-LTE computations.
---------------------------------------------------------
Title: What do astronomers want from the STFC?
Authors: Serjeant, Stephen; Bolton, James; Gandhi, Poshak; Helling,
Christiane; Mazzali, Paolo; Stappers, Ben; Unruh, Yvonne; Verma,
Aprajita
2019A&G....60b2.13S Altcode:
Stephen Serjeant and the STFC's Astronomy Advisory Panel summarize
community responses to its consultation on research priorities,
undertaken in November 2018.
---------------------------------------------------------
Title: ACTReSS: ACTive Rotating Star Simulator
Authors: Johnson, Luke Jonathan; Norris, Charlotte; Unruh, Yvonne;
Solanki, Sami; Krivova, Natalie
2018csss.confE..58J Altcode:
Variability of late-type stars on timescales of days or longer is
largely due to magnetic surface features (starspots and faculae). We
present ACTReSS, a software tool to calculate rotational lightcurves
of stars. The model uses limb-dependent intensities derived from
MURaM 3-D magneto-convection simulations (Beeck et al. 2014) for
quiet stellar photospheres and bright active regions. This allows us
to investigate the dependence of the flux variation on spectral type,
inclination and wavelength.
---------------------------------------------------------
Title: Reconstructing Total Solar Irradiance with the help of MHD
simulations
Authors: Leng Yeo, Kok; Solanki, Sami; Noris, Charlotte; Unruh,
Yvonne; Krivova, Natalie; Beeck, Benjamin
2018EGUGA..20.8166L Altcode:
The variation in the solar irradiance is an important input into the
climate system. Whereas it is commonly thought that solar irradiance
variability is driven by the evolving surface magnetism, verifying this
assumption has been more difficult. Making use of 3D MHD simulations
of the solar atmosphere layers and state-of-the-art solar magnetograms
from the Solar Dynamics Observatory, we present a model of total solar
irradiance (TSI) that does not require any calibration of the modeled
TSI by the measured TSI. I.e., the modeled irradiance variability
is entirely independent of the observational record, except for the
absolute level. The model replicates 95% of the observed variability
between April 2010 and July 2016, leaving little scope for alternative
drivers of solar irradiance variability, at least over the time scales
examined (days to years).
---------------------------------------------------------
Title: Effect of stellar flares on the upper atmospheres of HD
189733b and HD 209458b
Authors: Chadney, J. M.; Koskinen, T. T.; Galand, M.; Unruh, Y. C.;
Sanz-Forcada, J.
2017A&A...608A..75C Altcode: 2017arXiv171008365C
Stellar flares are a frequent occurrence on young low-mass stars around
which many detected exoplanets orbit. Flares are energetic, impulsive
events, and their impact on exoplanetary atmospheres needs to be taken
into account when interpreting transit observations. We have developed
a model to describe the upper atmosphere of extrasolar giant planets
(EGPs) orbiting flaring stars. The model simulates thermal escape from
the upper atmospheres of close-in EGPs. Ionisation by solar radiation
and electron impact is included and photo-chemical and diffusive
transport processes are simulated. This model is used to study the
effect of stellar flares from the solar-like G star <ASTROBJ>HD
209458</ASTROBJ> and the young K star <ASTROBJ>HD 189733</ASTROBJ>
on their respective planets, <ASTROBJ>HD 209458b</ASTROBJ> and
<ASTROBJ>HD 189733b</ASTROBJ>. The <ASTROBJ>Sun</ASTROBJ> is used as
a proxy for HD 209458, and <ASTROBJ>ɛ Eridani</ASTROBJ>, as a proxy
for HD 189733. A hypothetical HD 209458b-like planet orbiting the very
active M star <ASTROBJ>AU Microscopii</ASTROBJ> is also simulated. We
find that the neutral upper atmosphere of EGPs is not significantly
affected by typical flares on HD 209458 and HD 189733. Therefore,
stellar flares alone would not cause large enough changes in planetary
mass loss to explain the variations in HD 189733b transit depth seen
in previous studies, although we show that it may be possible that
an extreme stellar proton event could result in the required mass
loss. Our simulations do however reveal an enhancement in electron
number density in the ionosphere of these planets, the peak of which
is located in the layer where stellar X-rays are absorbed. Electron
densities are found to reach 2.2 to 3.5 times pre-flare levels and
enhanced electron densities last from about 3 to 10 h after the
onset of the flare, depending on the composition of the ionospheric
layer. The strength of the flare and the width of its spectral energy
distribution affect the range of altitudes in the ionosphere that see
enhancements in ionisation. A large broadband continuum component in
the XUV portion of the flaring spectrum in very young flare stars, such
as AU Mic, results in a broad range of altitudes affected in planets
orbiting this star. Indeed, as well as the X-ray absorption layer,
the layer in which EUV photons are absorbed is also strongly enhanced.
---------------------------------------------------------
Title: Spectral variability of photospheric radiation due to
faculae. I. The Sun and Sun-like stars
Authors: Norris, Charlotte M.; Beeck, Benjamin; Unruh, Yvonne C.;
Solanki, Sami K.; Krivova, Natalie A.; Yeo, Kok Leng
2017A&A...605A..45N Altcode: 2017arXiv170504455N
Context. Stellar spectral variability on timescales of a day and
longer, arising from magnetic surface features such as dark spots
and bright faculae, is an important noise source when characterising
extra-solar planets. Current 1D models of faculae do not capture the
geometric properties and fail to reproduce observed solar facular
contrasts. Magnetoconvection simulations provide facular contrasts
accounting for geometry. <BR /> Aims: We calculate facular contrast
spectra from magnetoconvection models of the solar photosphere with
a view to improve (a) future parameter determinations for planets
with early G type host stars and (b) reconstructions of solar spectral
variability. <BR /> Methods: Regions of a solar twin (G2, log g = 4.44)
atmosphere with a range of initial average vertical magnetic fields
(100 to 500 G) were simulated using a 3D radiation-magnetohydrodynamics
code, MURaM, and synthetic intensity spectra were calculated from
the ultraviolet (149.5 nm) to the far infrared (160 000 nm) with the
ATLAS9 radiative transfer code. Nine viewing angles were investigated
to account for facular positions across most of the stellar disc. <BR
/> Results: Contrasts of the radiation from simulation boxes with
different levels of magnetic flux relative to an atmosphere with no
magnetic field are a complicated function of position, wavelength
and magnetic field strength that is not reproduced by 1D facular
models. Generally, contrasts increase towards the limb, but at UV
wavelengths a saturation and decrease are observed close to the
limb. Contrasts also increase strongly from the visible to the UV;
there is a rich spectral dependence, with marked peaks in molecular
bands and strong spectral lines. At disc centre, a complex relationship
with magnetic field was found and areas of strong magnetic field
can appear either dark or bright, depending on wavelength. Spectra
calculated for a wide variety of magnetic fluxes will also serve to
improve total and spectral solar irradiance reconstructions.
---------------------------------------------------------
Title: Solar Irradiance Variability is Caused by the Magnetic Activity
on the Solar Surface
Authors: Yeo, K. L.; Solanki, S. K.; Norris, C. M.; Beeck, B.; Unruh,
Y. C.; Krivova, N. A.
2017PhRvL.119i1102Y Altcode: 2017arXiv170900920Y
The variation in the radiative output of the Sun, described in terms
of solar irradiance, is important to climatology. A common assumption
is that solar irradiance variability is driven by its surface
magnetism. Verifying this assumption has, however, been hampered by
the fact that models of solar irradiance variability based on solar
surface magnetism have to be calibrated to observed variability. Making
use of realistic three-dimensional magnetohydrodynamic simulations
of the solar atmosphere and state-of-the-art solar magnetograms from
the Solar Dynamics Observatory, we present a model of total solar
irradiance (TSI) that does not require any such calibration. In doing
so, the modeled irradiance variability is entirely independent of the
observational record. (The absolute level is calibrated to the TSI
record from the Total Irradiance Monitor.) The model replicates 95%
of the observed variability between April 2010 and July 2016, leaving
little scope for alternative drivers of solar irradiance variability
at least over the time scales examined (days to years).
---------------------------------------------------------
Title: VizieR Online Data Catalog: New OB star candidates in Carina
Arm (Mohr-Smith+, 2015)
Authors: Mohr-Smith, M.; Drew, J. E.; Barentsen, G.; Wright, N. J.;
Napiwotzki, R.; Corradi, R. L. M.; Eisloffel, J.; Groot, P.; Kalari,
V.; Parker, Q. A.; Raddi, R.; Sale, S. E.; Unruh, Y. C.; Vink, J. S.;
Wesson, R.
2017yCat..74503855M Altcode:
We make use of the photometry from two VPHAS+ fields, numbered 1678 and
1679, that are, respectively, centred on RA=10:18:10.91, DE=-58:03:52.3
(J2000) and on RA=10:25:27.27, DE=-58:03:52.3 (J2000). These were
observed in succession in the u, g and r filters on the night of 2012
January 22. The red filter data in Hα, r and i were obtained on 2012
April 29. <P />(2 data files).
---------------------------------------------------------
Title: The VST Photometric Halpha Survey of the Southern Galactic
Plane and Bulge (VPHAS+). Second VPHAS data release (DR2).
Authors: Drew, J. E.; Gonzales-Solares, E.; Greimel, R.; Irwin, M. J.;
Kupcu Yoldas, A.; Lewis, J.; Barentsen, G.; Eisloffel, J.; Farnhill,
H. J.; Martin, W. E.; Walsh, J. R.; Walton, N. A.; Mohr-Smith, M.;
Raddi, R.; Sale, S. E.; Wright, N. J.; Groot, P.; Barlow, M. J.;
Corradi, R. L. M.; Drake, J. J.; Fabregat, J.; Frew, D. J.; Gansicke,
B. T.; Knigge, C.; Mampaso, A.; Morris, R. A. H.; Naylor, T.; Parker,
Q. A.; Phillipps, S.; Ruhland, C.; Steeghs, D.; Unruh, Y. C.; Vink,
J. S.; Wesson, R.; Zijlstra, A. A.
2016yCat.2341....0D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Modelling the Spectral Contrasts of Stellar Faculae.
Authors: Norris, Charlotte M.; Beeck, Benjamin; Unruh, Yvonne; Solanki,
Sami; Yeo, Kok Leng; Krivova, Natalie
2016csss.confE..63N Altcode:
Facular contrasts are an important parameter in modelling stellar
variability and exoplanet transits. The ultimate goal of this work
will be to model the contrasts of faculae for different spectral types
and thus improve the modelling of solar and stellar photospheric
variability. This is done by using a radiative transfer algorithm
(ATLAS9) on magneto-convection simulations. Starting with solar twins,
we derive facular contrasts as a function of limb angle and discuss
their wavelength dependence.
---------------------------------------------------------
Title: Reconstruction of spectral solar irradiance since 1700 from
simulated magnetograms
Authors: Dasi-Espuig, M.; Jiang, J.; Krivova, N. A.; Solanki, S. K.;
Unruh, Y. C.; Yeo, K. L.
2016A&A...590A..63D Altcode: 2016arXiv160502039D
<BR /> Aims: We present a reconstruction of the spectral solar
irradiance since 1700 using the SATIRE-T2 (Spectral And Total Irradiance
REconstructions for the Telescope era version 2) model. This model
uses as input magnetograms simulated with a surface flux transport
model fed with semi-synthetic records of emerging sunspot groups. <BR
/> Methods: The record of sunspot group areas and positions from the
Royal Greenwich Observatory (RGO) is only available since 1874. We
used statistical relationships between the properties of sunspot
group emergence, such as the latitude, area, and tilt angle, and the
sunspot cycle strength and phase to produce semi-synthetic sunspot
group records starting in the year 1700. The semi-synthetic records
are fed into a surface flux transport model to obtain daily simulated
magnetograms that map the distribution of the magnetic flux in active
regions (sunspots and faculae) and their decay products on the solar
surface. The magnetic flux emerging in ephemeral regions is accounted
for separately based on the concept of extended cycles whose length
and amplitude are linked to those of the sunspot cycles through the
sunspot number. The magnetic flux in each surface component (sunspots,
faculae and network, and ephemeral regions) was used to compute the
spectral and total solar irradiance (TSI) between the years 1700
and 2009. This reconstruction is aimed at timescales of months or
longer although the model returns daily values. <BR /> Results: We
found that SATIRE-T2, besides reproducing other relevant observations
such as the total magnetic flux, reconstructs the TSI on timescales
of months or longer in good agreement with the PMOD composite of
observations, as well as with the reconstruction starting in 1878
based on the RGO-SOON data. The model predicts an increase in the TSI
of 1.2<SUP>+0.2</SUP><SUB>-0.3</SUB> Wm<SUP>-2</SUP> between 1700
and the present. The spectral irradiance reconstruction is in good
agreement with the UARS/SUSIM measurements as well as the Lyman-α
composite. <P />The complete total and spectral (115 nm-160 μm)
irradiance reconstructions since 1700 will be available from <A
href="http://www2.mps.mpg.de/projects/sun-climate/data.html">http://www2.mps.mpg.de/projects/sun-climate/data.html</A>
---------------------------------------------------------
Title: The Sun as a planet-host star: proxies from SDO images for
HARPS radial-velocity variations
Authors: Haywood, R. D.; Collier Cameron, A.; Unruh, Y. C.; Lovis,
C.; Lanza, A. F.; Llama, J.; Deleuil, M.; Fares, R.; Gillon, M.;
Moutou, C.; Pepe, F.; Pollacco, D.; Queloz, D.; Ségransan, D.
2016MNRAS.457.3637H Altcode: 2016arXiv160105651H
The Sun is the only star whose surface can be directly resolved at
high resolution, and therefore constitutes an excellent test case
to explore the physical origin of stellar radial-velocity (RV)
variability. We present HARPS observations of sunlight scattered
off the bright asteroid 4/Vesta, from which we deduced the Sun's
activity-driven RV variations. In parallel, the Helioseismic and
Magnetic Imager instrument on board the Solar Dynamics Observatory
provided us with simultaneous high spatial resolution magnetograms,
Dopplergrams and continuum images of the Sun in the Fe I 6173 Å
line. We determine the RV modulation arising from the suppression of
granular blueshift in magnetized regions and the flux imbalance induced
by dark spots and bright faculae. The rms velocity amplitudes of these
contributions are 2.40 and 0.41 m s<SUP>-1</SUP>, respectively, which
confirms that the inhibition of convection is the dominant source of
activity-induced RV variations at play, in accordance with previous
studies. We find the Doppler imbalances of spot and plage regions to be
only weakly anticorrelated. Light curves can thus only give incomplete
predictions of convective blueshift suppression. We must instead seek
proxies that track the plage coverage on the visible stellar hemisphere
directly. The chromospheric flux index R^' }_{HK} derived from the
HARPS spectra performs poorly in this respect, possibly because of
the differences in limb brightening/darkening in the chromosphere and
photosphere. We also find that the activity-driven RV variations of the
Sun are strongly correlated with its full-disc magnetic flux density,
which may become a useful proxy for activity-related RV noise.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Lagoon Nebula M8 T tauri accretion
rates (Kalari+, 2015)
Authors: Kalari, V. M.; Vink, J. S.; Drew, J. E.; Barentsen, G.;
Drake, J. J.; Eisloffel, J.; Martin, E. L.; Parker, Q. A.; Unruh,
Y. C.; Walton, N. A.; Wright, N. J.
2016yCat..74531026K Altcode:
VPHAS+ imaging is obtained by the OmegaCAM CCD imager mounted on
the 2.6m VLT Survey Telescope (VST) on Cerro Paranal, Chile. The
imager captures a 1° square field of view at a resolution of
0.21arcsec/pix. Each pointing is supplemented by at least one offset
exposure to minimize CCD gaps. Imaging is carried out through broad-band
ugri filters and a purpose-built Hα filter. The central wavelength and
bandpass of the Hα filter are 6588 and 107Å, respectively. Exposure
times are 150, 30, 25, 25, and 120s, respectively. VPHAS+ reaches a
5σ depth at Hα=20.5-21.0mag and g=22.2-22.7mag. Practical constraints
have meant that the blue (ug) and red (riHα) observations are carried
out separately. An additional r observation is carried out with every
blue observation to serve as a linking reference. <P />(2 data files).
---------------------------------------------------------
Title: EUV-driven ionospheres and electron transport on extrasolar
giant planets orbiting active stars
Authors: Chadney, J. M.; Galand, M.; Koskinen, T. T.; Miller, S.;
Sanz-Forcada, J.; Unruh, Y. C.; Yelle, R. V.
2016A&A...587A..87C Altcode: 2016arXiv160103216C
The composition and structure of the upper atmospheres of extrasolar
giant planets (EGPs) are affected by the high-energy spectrum of their
host stars from soft X-rays to the extreme ultraviolet (EUV). This
emission depends on the activity level of the star, which is primarily
determined by its age. In this study, we focus upon EGPs orbiting K-
and M-dwarf stars of different ages - <ASTROBJ>ɛ Eridani</ASTROBJ>,
<ASTROBJ>AD Leonis</ASTROBJ>, <ASTROBJ>AU Microscopii</ASTROBJ>
- and the <ASTROBJ>Sun</ASTROBJ>. X-ray and EUV (XUV) spectra for
these stars are constructed using a coronal model. These spectra
are used to drive both a thermospheric model and an ionospheric
model, providing densities of neutral and ion species. Ionisation -
as a result of stellar radiation deposition - is included through
photo-ionisation and electron-impact processes. The former is calculated
by solving the Lambert-Beer law, while the latter is calculated from a
supra-thermal electron transport model. We find that EGP ionospheres
at all orbital distances considered (0.1-1 AU) and around all stars
selected are dominated by the long-lived H<SUP>+</SUP> ion. In
addition, planets with upper atmospheres where H<SUB>2</SUB> is not
substantially dissociated (at large orbital distances) have a layer
in which H<SUB>3</SUB><SUP>+</SUP> is the major ion at the base of
the ionosphere. For fast-rotating planets, densities of short-lived
H<SUB>3</SUB><SUP>+</SUP> undergo significant diurnal variations,
with the maximum value being driven by the stellar X-ray flux. In
contrast, densities of longer-lived H<SUP>+</SUP> show very little
day/night variability and the magnitude is driven by the level of
stellar EUV flux. The H<SUB>3</SUB><SUP>+</SUP> peak in EGPs with
upper atmospheres where H<SUB>2</SUB> is dissociated (orbiting close to
their star) under strong stellar illumination is pushed to altitudes
below the homopause, where this ion is likely to be destroyed through
reactions with heavy species (e.g. hydrocarbons, water). The inclusion
of secondary ionisation processes produces significantly enhanced ion
and electron densities at altitudes below the main EUV ionisation peak,
as compared to models that do not include electron-impact ionisation. We
estimate infrared emissions from H<SUB>3</SUB><SUP>+</SUP>, and while,
in an H/H<SUB>2</SUB>/He atmosphere, these are larger from planets
orbiting close to more active stars, they still appear too low to be
detected with current observatories.
---------------------------------------------------------
Title: Classical T Tauri stars with VPHAS+ - I. H α and u-band
accretion rates in the Lagoon Nebula M8
Authors: Kalari, V. M.; Vink, J. S.; Drew, J. E.; Barentsen, G.;
Drake, J. J.; Eislöffel, J.; Martín, E. L.; Parker, Q. A.; Unruh,
Y. C.; Walton, N. A.; Wright, N. J.
2015MNRAS.453.1026K Altcode: 2015arXiv150706786K
We estimate the accretion rates of 235 Classical T Tauri star (CTTS)
candidates in the Lagoon Nebula using ugri H α photometry from the VST
Photometric H α survey+. Our sample consists of stars displaying H α
excess, the intensity of which is used to derive accretion rates. For a
subset of 87 stars, the intensity of the u-band excess is also used to
estimate accretion rates. We find the mean variation in accretion rates
measured using H α and u-band intensities to be ∼0.17 dex, agreeing
with previous estimates (0.04-0.4 dex) but for a much larger sample. The
spatial distribution of CTTS align with the location of protostars and
molecular gas suggesting that they retain an imprint of the natal gas
fragmentation process. Strong accretors are concentrated spatially,
while weak accretors are more distributed. Our results do not support
the sequential star-forming processes suggested in the literature.
---------------------------------------------------------
Title: Modelling the ionosphere of gas-giant exoplanets irradiated
by low-mass stars
Authors: Chadney, J.; Galand, M.; Unruh, Y.; Koskinen, T.;
Sanz-Forcada, J.
2015EPSC...10..307C Altcode:
The composition and structure of the upper atmosphere of Extrasolar
Giant Planets (EGPs) are affected by the high-energy spectrum of
the host star from soft X-rays to Extreme UltraViolet (EUV) (0.1-10
nm). This emission depends on the activity level of the star, which is
primarily determined by its age [1]. In this study, we focus upon EGPs
orbiting K- and M-dwarf stars of different ages. XUV spectra for these
stars are constructed using a coronal model [2]. These spectra are used
to drive both a thermospheric [3] and an ionospheric model, providing
densities of neutral and ion species. Ionisation is included through
photo-ionisation and electronimpact processes. The former is calculated
by solving the Lambert-Beer law, while the latter is calculated from a
supra-thermal electron transport model [4]. Planets orbiting far from
the star are found to undergo Jeans escape, whereas close-orbiting
planets undergo hydrodynamic escape. The critical orbital distance of
transition between the two regimes is dependent on the level of stellar
activity. We also find that EGP ionospheres at all orbital distances
considered (0.1-1 AU) and around all stars selected (eps Eri, AD Leo,
AU Mic) are dominated by the long-lived H+ ion. In addition, planets
in the Jeans escape regime also have a layer in which H3 + is the major
ion at the base of the ionosphere. For fast-rotating planets, densities
of short-lived H3 + undergo significant diurnal variations, their
peak value being determined by the stellar X-ray flux. In contrast,
densities of longer-lived H+ show very little day/night variability and
their value is determined by the level of stellar EUV flux. The H3 +
peak in EGPs in the hydrodynamic escape regime under strong stellar
illumination is pushed to altitudes below the homopause, where this
ion is likely to be destroyed through reactions with heavy species
(e.g., hydrocarbons, water). Infrared emissions from H3 + shall also
be discussed, as well as the impact of stellar variability.
---------------------------------------------------------
Title: UV solar irradiance in observations and the NRLSSI and
SATIRE-S models
Authors: Yeo, K. L.; Ball, W. T.; Krivova, N. A.; Solanki, S. K.;
Unruh, Y. C.; Morrill, J.
2015JGRA..120.6055Y Altcode: 2015arXiv150701224Y
Total solar irradiance and UV spectral solar irradiance has been
monitored since 1978 through a succession of space missions. This is
accompanied by the development of models aimed at replicating solar
irradiance by relating the variability to solar magnetic activity. The
Naval Research Laboratory Solar Spectral Irradiance (NRLSSI) and
Spectral And Total Irradiance REconstruction for the Satellite era
(SATIRE-S) models provide the most comprehensive reconstructions of
total and spectral solar irradiance over the period of satellite
observation currently available. There is persistent controversy
between the various measurements and models in terms of the wavelength
dependence of the variation over the solar cycle, with repercussions on
our understanding of the influence of UV solar irradiance variability
on the stratosphere. We review the measurement and modeling of UV solar
irradiance variability over the period of satellite observation. The
SATIRE-S reconstruction is consistent with spectral solar irradiance
observations where they are reliable. It is also supported by an
independent, empirical reconstruction of UV spectral solar irradiance
based on Upper Atmosphere Research Satellite/Solar Ultraviolet Spectral
Irradiance Monitor measurements from an earlier study. The weaker
solar cycle variability produced by NRLSSI between 300 and 400 nm is
not evident in any available record. We show that although the method
employed to construct NRLSSI is principally sound, reconstructed solar
cycle variability is detrimentally affected by the uncertainty in the
SSI observations it draws upon in the derivation. Based on our findings,
we recommend, when choosing between the two models, the use of SATIRE-S
for climate studies.
---------------------------------------------------------
Title: New OB star candidates in the Carina Arm around Westerlund
2 from VPHAS+
Authors: Mohr-Smith, M.; Drew, J. E.; Barentsen, G.; Wright, N. J.;
Napiwotzki, R.; Corradi, R. L. M.; Eislöffel, J.; Groot, P.; Kalari,
V.; Parker, Q. A.; Raddi, R.; Sale, S. E.; Unruh, Y. C.; Vink, J. S.;
Wesson, R.
2015MNRAS.450.3855M Altcode: 2015arXiv150404342M
O and early B stars are at the apex of galactic ecology, but in the
Milky Way, only a minority of them may yet have been identified. We
present the results of a pilot study to select and parametrize OB star
candidates in the Southern Galactic plane, down to a limiting magnitude
of g = 20. A 2 deg<SUP>2</SUP> field capturing the Carina Arm around the
young massive star cluster, Westerlund 2, is examined. The confirmed OB
stars in this cluster are used to validate our identification method,
based on selection from the (u - g, g - r) diagram for the region. Our
Markov Chain Monte Carlo fitting method combines VPHAS+ u, g, r, i with
published J, H, K photometry in order to derive posterior probability
distributions of the stellar parameters log (T<SUB>eff</SUB>) and
distance modulus, together with the reddening parameters A<SUB>0</SUB>
and R<SUB>V</SUB>. The stellar parameters are sufficient to confirm OB
status while the reddening parameters are determined to a precision of
σ(A<SUB>0</SUB>) ∼ 0.09 and σ(R<SUB>V</SUB>) ∼ 0.08. There are 489
objects that fit well as new OB candidates, earlier than ∼B2. This
total includes 74 probable massive O stars, 5 likely blue supergiants
and 32 reddened subdwarfs. This increases the number of previously
known and candidate OB stars in the region by nearly a factor of
10. Most of the new objects are likely to be at distances between 3
and 6 kpc. We have confirmed the results of previous studies that,
at these longer distances, these sight lines require non-standard
reddening laws with 3.5 < R<SUB>V</SUB> < 4.
---------------------------------------------------------
Title: VizieR Online Data Catalog: VPHAS+ survey synthetic colours
(Drew+, 2014)
Authors: Drew, J. E.; Gonzalez-Solares, E.; Greimel, R.; Irwin, M. J.;
Kupcu Yoldas, A.; Lewis, J.; Barentsen, G.; Eisloffel, J.; Farnhill,
H. J.; Martin, W. E.; Walsh, J. R.; Walton, N. A.; Mohr-Smith, M.;
Raddi, R.; Sale, S. E.; Wright, N. J.; Groot, P.; Barlow, M. J.;
Corradi, R. L. M.; Drake, J. J.; Fabregat, J.; Frew, D. J.; Gansicke,
B. T.; Knigge, C.; Mampaso, A.; Morris, R. A. H.; Naylor, T.; Parker,
Q. A.; Phillipps, S.; Ruhland, C.; Steeghs, D.; Unruh, Y. C.; Vink,
J. S.; Wesson, R.; Zijlstra, A. A.
2015yCat..74402036D Altcode:
Synthetic colours for main sequence stars, computed as described in
Section 4 from model atmospheres, are here tabulated in full for three
representative reddening laws (R<SUB>V</SUB> = 2.5, 3.1 and 3.8) and a
range of reddenings (A0 = 0, 2, 4, 6, 8, 10). The form of the reddening
laws used is due to Fitzpatrick & Massa (2007ApJ...663..320F,
Cat. J/ApJ/663/320). When using the blue-filter tables, it should be
borne in mind that beyond g-r~3, the red leak in the u filter signif-
icantly alters u-g. In this domain we expect the synthetic colours
to progressively become less reliable as they increas- ingly depend
on hard-to-measure very low levels of red trans- mission. Objects
that appear to have these extreme, peculiar colours are likely to be
reddened red giants or supergiants, since reddened K-M main sequence
stars are too faint to be detected in VPHAS+ exposures. Beyond g-r~3.5
these table entries are italicised. Two further tables of synthetic
colours are included for K-M giants that have been computed using
P98 library spectra. Data are provided for the R<SUB>V</SUB>=3.1 mean
Galactic law only, for the limited purposes of (a) giving an impres-
sion of how these luminous red objects may contaminate (u-g, g-r)
diagrams at redder (g-r) through u red leak (b) enabling comparisons
with the M-giant spur commonly seen in (r-Hα, r-i) colour-colour
diagrams. <P />(8 data files).
---------------------------------------------------------
Title: XUV-driven mass loss from extrasolar giant planets orbiting
active stars
Authors: Chadney, J. M.; Galand, M.; Unruh, Y. C.; Koskinen, T. T.;
Sanz-Forcada, J.
2015Icar..250..357C Altcode: 2014arXiv1412.3380C
Upper atmospheres of Hot Jupiters are subject to extreme radiation
conditions that can result in rapid atmospheric escape. The composition
and structure of the upper atmospheres of these planets are affected
by the high-energy spectrum of the host star. This emission depends on
stellar type and age, which are thus important factors in understanding
the behaviour of exoplanetary atmospheres. In this study, we focus
on Extrasolar Giant Planets (EPGs) orbiting K and M dwarf stars. XUV
spectra for three different stars - ɛ Eridani, AD Leonis and AU
Microscopii - are constructed using a coronal model. Neutral density
and temperature profiles in the upper atmosphere of hypothetical
EGPs orbiting these stars are then obtained from a fluid model,
incorporating atmospheric chemistry and taking atmospheric escape into
account. We find that a simple scaling based solely on the host star's
X-ray emission gives large errors in mass loss rates from planetary
atmospheres and so we have derived a new method to scale the EUV
regions of the solar spectrum based upon stellar X-ray emission. This
new method produces an outcome in terms of the planet's neutral upper
atmosphere very similar to that obtained using a detailed coronal model
of the host star. Our results indicate that in planets subjected to
radiation from active stars, the transition from Jeans escape to a
regime of hydrodynamic escape at the top of the atmosphere occurs at
larger orbital distances than for planets around low activity stars
(such as the Sun).
---------------------------------------------------------
Title: The second data release of the INT Photometric Hα Survey of
the Northern Galactic Plane (IPHAS DR2)
Authors: Barentsen, Geert; Farnhill, H. J.; Drew, J. E.;
González-Solares, E. A.; Greimel, R.; Irwin, M. J.; Miszalski, B.;
Ruhland, C.; Groot, P.; Mampaso, A.; Sale, S. E.; Henden, A. A.;
Aungwerojwit, A.; Barlow, M. J.; Carter, P. J.; Corradi, R. L. M.;
Drake, J. J.; Eislöffel, J.; Fabregat, J.; Gänsicke, B. T.; Gentile
Fusillo, N. P.; Greiss, S.; Hales, A. S.; Hodgkin, S.; Huckvale, L.;
Irwin, J.; King, R.; Knigge, C.; Kupfer, T.; Lagadec, E.; Lennon,
D. J.; Lewis, J. R.; Mohr-Smith, M.; Morris, R. A. H.; Naylor, T.;
Parker, Q. A.; Phillipps, S.; Pyrzas, S.; Raddi, R.; Roelofs, G. H. A.;
Rodríguez-Gil, P.; Sabin, L.; Scaringi, S.; Steeghs, D.; Suso, J.;
Tata, R.; Unruh, Y. C.; van Roestel, J.; Viironen, K.; Vink, J. S.;
Walton, N. A.; Wright, N. J.; Zijlstra, A. A.
2014MNRAS.444.3230B Altcode: 2014arXiv1406.4862B
The INT/WFC Photometric Hα Survey of the Northern Galactic Plane
(IPHAS) is a 1800 deg<SUP>2</SUP> imaging survey covering Galactic
latitudes |b| < 5° and longitudes ℓ = 30°-215° in the r, i, and
Hα filters using the Wide Field Camera (WFC) on the 2.5-m Isaac Newton
Telescope (INT) in La Palma. We present the first quality-controlled
and globally calibrated source catalogue derived from the survey,
providing single-epoch photometry for 219 million unique sources
across 92 per cent of the footprint. The observations were carried out
between 2003 and 2012 at a median seeing of 1.1 arcsec (sampled at 0.33
arcsec pixel<SUP>-1</SUP>) and to a mean 5σ depth of 21.2 (r), 20.0
(i), and 20.3 (Hα) in the Vega magnitude system. We explain the data
reduction and quality control procedures, describe and test the global
re-calibration, and detail the construction of the new catalogue. We
show that the new calibration is accurate to 0.03 mag (root mean square)
and recommend a series of quality criteria to select accurate data from
the catalogue. Finally, we demonstrate the ability of the catalogue's
unique (r - Hα, r - i) diagram to (i) characterize stellar populations
and extinction regimes towards different Galactic sightlines and (ii)
select and quantify Hα emission-line objects. IPHAS is the first
survey to offer comprehensive CCD photometry of point sources across
the Galactic plane at visible wavelengths, providing the much-needed
counterpart to recent infrared surveys.
---------------------------------------------------------
Title: A New SATIRE-S Spectral Solar Irradiance Reconstruction for
Solar Cycles 21-23 and Its Implications for Stratospheric Ozone*
Authors: Ball, William T.; Krivova, Natalie A.; Unruh, Yvonne C.;
Haigh, Joanna D.; Solanki, Sami K.
2014JAtS...71.4086B Altcode: 2014arXiv1408.0365B
We present a revised and extended total and spectral solar irradiance
(SSI) reconstruction, which includes a wavelength-dependent uncertainty
estimate, spanning the last three solar cycles using the SATIRE-S
model. The SSI reconstruction covers wavelengths between 115 and
160,000 nm and all dates between August 1974 and October 2009. This
represents the first full-wavelength SATIRE-S reconstruction to
cover the last three solar cycles without data gaps and with an
uncertainty estimate. SATIRE-S is compared with the NRLSSI model and
SORCE/SOLSTICE ultraviolet (UV) observations. SATIRE-S displays similar
cycle behaviour to NRLSSI for wavelengths below 242 nm and almost twice
the variability between 242 and 310 nm. During the decline of last
solar cycle, between 2003 and 2008, SSI from SORCE/SOLSTICE version
12 and 10 typically displays more than three times the variability of
SATIRE-S between 200 and 300 nm. All three datasets are used to model
changes in stratospheric ozone within a 2D atmospheric model for a
decline from high solar activity to solar minimum. The different flux
changes result in different modelled ozone trends. Using NRLSSI leads
to a decline in mesospheric ozone, while SATIRE-S and SORCE/SOLSTICE
result in an increase. Recent publications have highlighted increases
in mesospheric ozone when considering version 10 SORCE/SOLSTICE
irradiances. The recalibrated SORCE/SOLSTICE version 12 irradiances
result in a much smaller mesospheric ozone response than when using
version 10 and now similar in magnitude to SATIRE-S. This shows that
current knowledge of variations in spectral irradiance is not sufficient
to warrant robust conclusions concerning the impact of solar variability
on the atmosphere and climate.
---------------------------------------------------------
Title: Variability of Sun-like stars: reproducing observed photometric
trends
Authors: Shapiro, A. I.; Solanki, S. K.; Krivova, N. A.; Schmutz,
W. K.; Ball, W. T.; Knaack, R.; Rozanov, E. V.; Unruh, Y. C.
2014A&A...569A..38S Altcode: 2014arXiv1406.2383S
Context. The Sun and stars with low magnetic activity levels become
photometrically brighter when their activity increases. Magnetically
more active stars display the opposite behavior and become fainter
when their activity increases. <BR /> Aims: We reproduce the observed
photometric trends in stellar variations with a model thattreats stars
as hypothetical suns with coverage by magnetic features different from
that of the Sun. <BR /> Methods: The model attributes the variability
of stellar spectra to the imbalance between the contributions from
different components of the solar atmosphere, such as dark starspots
and bright faculae. A stellar spectrum is calculated from spectra
of the individual components by weighting them with corresponding
disk-area coverages. The latter are obtained by extrapolating
the solar dependences of spot and facular disk-area coverages
on chromospheric activity to stars with different levels of mean
chromospheric activity. <BR /> Results: We find that the contribution
by starspots to the variability increases faster with chromospheric
activity than the facular contribution. This causes the transition from
faculae-dominated variability and direct activity-brightness correlation
to spot-dominated variability and inverse activity-brightness
correlation with increasing chromospheric activity level. We show that
the regime of the variability also depends on the angle between the
stellar rotation axis and the line-of-sight and on the latitudinal
distribution of active regions on the stellar surface. Our model
can be used as a tool for extrapolating the observed photometric
variability of the Sun to Sun-like stars at different activity levels,
which makes a direct comparison between solar and stellar irradiance
data possible. <P />Appendices are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201323086/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: VizieR Online Data Catalog: IPHAS DR2 Source Catalogue
(Barentsen+, 2014)
Authors: Barentsen, G.; Farnhill, H. J.; Drew, J. E.; Gonzalez-Solares,
E. A.; Greimel, R.; Irwin, M. J.; Miszalski, B.; Ruhland, C.; Groot,
P.; Mampaso, A.; Sale, S. E.; Henden, A. A.; Aungwerojwit, A.; Barlow,
M. J.; Carter, P. J.; Corradi, R. L. M.; Drake, J. J.; Eisloffel, J.;
Fabregat, J.; Gansicke, B. T.; Gentile Fusillo, N. P.; Greiss, S.;
Hales, A. S.; Hodgkin, S.; Huckvale, L.; Irwin, J.; King, R.; Knigge,
C.; Kupfer, T.; Lagadec, E.; Lennon, D. J.; Lewis, J. R.; Mohr-Smith,
M.; Morris, R. A. H.; Naylor, T.; Parker, Q. A.; Phillipps, S.;
Pyrzas, S.; Raddi, R.; Roelofs, G. H. A.; Rodriguez-Gil, P.; Sabin,
L.; Scaringi, S.; Steeghs, D.; Suso, J.; Tata, R.; Unruh, Y. C.;
van Roestel, J.; Viironen, K.; Vink, J. S.; Walton, N. A.; Wright,
N. J.; Zijlstra, A. A.
2014yCat.2321....0B Altcode:
The INT/WFC Photometric H-Alpha Survey of the Northern Galactic Plane
(IPHAS) is a 1860 deg<SUP>2</SUP> imaging survey of the Northern Milky
Way at red visible wavelengths. It covers Galactic latitudes |b|<5°
and longitudes l=30 to 215° in the broad-band r, i and narrow-band
H-alpha filters using the Wide Field Camera (WFC) on the 2.5-m Isaac
Newton Telescope (INT) in La Palma. <P />IPHAS Data Release 2 (DR2) is
the first quality-controlled and globally calibrated source catalogue
derived from the survey, providing single-epoch photometry for 219
million unique sources across 92% of the footprint. The observations
were carried out between 2003 and 2012 at a median seeing of 1.1 arcsec
(sampled at 0.33 arcsec/pixel) and to a mean 5-sigma depth of 21.2
(r), 20.0 (i) and 20.3 (H-alpha). The photometric calibration is in
the Vega magnitude system and carries an external precision of 0.03mag
(root-mean-square error). <P />The catalogue includes all the sources
which have been detected at a signal-to-noise ratio of 5 or better
in at least one band. Many applications will require a combination
of quality criteria to be applied to avoid faint stars or confused
sources. The choice of quality criteria tensions completeness against
reliability, and hence depends on the requirements of a project. To
aid users, the data release paper (arXiv:1406.4862) recommends two sets
of quality criteria, named "a10" and "a10point", which should satisfy
most projects. As a minimum, the "a10" criteria select objects which
have been detected at the minimum level of 10-sigma in all bands,
without being saturated. Additional constraints are provided by the
"a10point" criteria, which require objects to be point sources free
of blending, unaffected by nearby bright stars, as well as being
unsaturated >10-sigma detections in all bands. Sources in both
categories are flagged in the catalogue using the boolean columns a10
and a10point. <P />Imaging and auxiliary data are available from the
project website (www.iphas.org). <P />(1 data file).
---------------------------------------------------------
Title: Planets and stellar activity: hide and seek in the CoRoT-7
system
Authors: Haywood, R. D.; Collier Cameron, A.; Queloz, D.; Barros,
S. C. C.; Deleuil, M.; Fares, R.; Gillon, M.; Lanza, A. F.; Lovis,
C.; Moutou, C.; Pepe, F.; Pollacco, D.; Santerne, A.; Ségransan,
D.; Unruh, Y. C.
2014MNRAS.443.2517H Altcode: 2014arXiv1407.1044H
Since the discovery of the transiting super-Earth CoRoT-7b, several
investigations have yielded different results for the number and masses
of planets present in the system, mainly owing to the star's high level
of activity. We re-observed CoRoT-7 in 2012 January with both HARPS and
CoRoT, so that we now have the benefit of simultaneous radial-velocity
and photometric data. This allows us to use the off-transit variations
in the star's light curve to estimate the radial-velocity variations
induced by the suppression of convective blueshift and the flux blocked
by starspots. To account for activity-related effects in the radial
velocities which do not have a photometric signature, we also include
an additional activity term in the radial-velocity model, which we
treat as a Gaussian process with the same covariance properties (and
hence the same frequency structure) as the light curve. Our model
was incorporated into a Monte Carlo Markov Chain in order to make
a precise determination of the orbits of CoRoT-7b and CoRoT-7c. We
measure the masses of planets b and c to be 4.73 ± 0.95 and 13.56
± 1.08 M<SUB>⊕</SUB>, respectively. The density of CoRoT-7b is
(6.61 ± 1.72)(R<SUB>p</SUB>/1.58 R<SUB>⊕</SUB>)<SUP>-3</SUP> g
cm<SUP>-3</SUP>, which is compatible with a rocky composition. We search
for evidence of an additional planet d, identified by previous authors
with a period close to 9 d. We are not able to confirm the existence
of a planet with this orbital period, which is close to the second
harmonic of the stellar rotation at ∼7.9 d. Using Bayesian model
selection, we find that a model with two planets plus activity-induced
variations is most favoured.
---------------------------------------------------------
Title: The VST Photometric Hα Survey of the Southern Galactic Plane
and Bulge (VPHAS+)
Authors: Drew, J. E.; Gonzalez-Solares, E.; Greimel, R.; Irwin,
M. J.; Küpcü Yoldas, A.; Lewis, J.; Barentsen, G.; Eislöffel,
J.; Farnhill, H. J.; Martin, W. E.; Walsh, J. R.; Walton, N. A.;
Mohr-Smith, M.; Raddi, R.; Sale, S. E.; Wright, N. J.; Groot, P.;
Barlow, M. J.; Corradi, R. L. M.; Drake, J. J.; Fabregat, J.; Frew,
D. J.; Gänsicke, B. T.; Knigge, C.; Mampaso, A.; Morris, R. A. H.;
Naylor, T.; Parker, Q. A.; Phillipps, S.; Ruhland, C.; Steeghs, D.;
Unruh, Y. C.; Vink, J. S.; Wesson, R.; Zijlstra, A. A.
2014MNRAS.440.2036D Altcode: 2014arXiv1402.7024D; 2014MNRAS.tmp..599D; 2014MNRAS.tmp..608D
The VST Photometric Hα Survey of the Southern Galactic Plane and Bulge
(VPHAS+) is surveying the southern Milky Way in u, g, r, i and Hα
at ∼1 arcsec angular resolution. Its footprint spans the Galactic
latitude range -5<SUP>o</SUP> < b < +5° at all longitudes south
of the celestial equator. Extensions around the Galactic Centre to
Galactic latitudes ±10° bring in much of the Galactic bulge. This
European Southern Observatory public survey, begun on 2011 December 28,
reaches down to ∼20th magnitude (10σ) and will provide single-epoch
digital optical photometry for ∼300 million stars. The observing
strategy and data pipelining are described, and an appraisal of the
segmented narrow-band Hα filter in use is presented. Using model
atmospheres and library spectra, we compute main-sequence (u - g),
(g - r), (r - i) and (r - Hα) stellar colours in the Vega system. We
report on a preliminary validation of the photometry using test data
obtained from two pointings overlapping the Sloan Digital Sky Survey. An
example of the (u - g, g - r) and (r - Hα, r - i) diagrams for a full
VPHAS+ survey field is given. Attention is drawn to the opportunities
for studies of compact nebulae and nebular morphologies that arise
from the image quality being achieved. The value of the u band as the
means to identify planetary-nebula central stars is demonstrated by the
discovery of the central star of NGC 2899 in survey data. Thanks to its
excellent imaging performance, the VLT Survey Telescope (VST)/OmegaCam
combination used by this survey is a perfect vehicle for automated
searches for reddened early-type stars, and will allow the discovery
and analysis of compact binaries, white dwarfs and transient sources.
---------------------------------------------------------
Title: Disentangling planetary orbits from stellar activity in
radial-velocity surveys
Authors: Haywood, R. D.; Collier Cameron, A.; Queloz, D.; Barros,
S. C. C.; Deleuil, M.; Fares, R.; Gillon, M.; Hatzes, A.; Lanza,
A. F.; Lovis, C.; Moutou, C.; Pepe, F.; Pollacco, D.; Santerne, A.;
Ségransan, D.; Unruh, Y.
2014IJAsB..13..155H Altcode:
The majority of extra-solar planets have been discovered (or confirmed
after follow-up) through radial-velocity (RV) surveys. Using
ground-based spectrographs such as High Accuracy Radial Velocity
Planetary Search (HARPS) and HARPS-North, it is now possible to detect
planets that are only a few times the mass of the Earth. However, the
presence of dark spots on the stellar surface produces RV signals that
are very similar in amplitude to those caused by orbiting low-mass
planets. Disentangling these signals has thus become the biggest
challenge in the detection of Earth-mass planets using RV surveys. To do
so, we use the star's lightcurve to model the RV variations produced
by spots. Here we present this method and show the results of its
application to CoRoT-7.
---------------------------------------------------------
Title: Modelling of Hot Jupiter thermospheres and ionospheres under
irradiation from active stars
Authors: Chadney, J.; Galand, M.; Unruh, Y.; Koskinen, T.;
Sanz-Forcada, J.
2014EPSC....9..579C Altcode:
Upper atmospheres of Hot Jupiters are subject to extreme radiation
conditions that can result in atmospheric escape. The composition
and structure of the thermosphere and ionosphere of these planets are
affected by the high-energy spectrum of the host star. This emission
depends on stellar type and age, which are thus important factors in
understanding the behaviour of exoplanetary atmospheres. In this study,
we focus on Hot Jupiter planets orbiting K and M dwarf stars. As an
example, XUV spectra for three different stars - ɛ Eridani, AD Leonis
and AU Microscopii - are constructed using a coronal model. Neutral
density and temperature profiles in the thermosphere of hypothetical,
Hot Jupiters orbiting these stars are then obtained from a fluid
model of the upper atmosphere, incorporating atmospheric chemistry
and taking atmospheric escape into account. Using these models of both
the host star and the planetary atmosphere, we have derived a method
to scale the X-ray and EUV regions of the solar spectrum to produce
a very similar outcome in terms of the planet's neutral thermosphere
as using a detailed coronal model of the host star. We also calculate
ion production rates and densities in the ionospheres of such planets,
considering ionisation through both photo-ionisation and electronimpact
processes. We find that in planets subjected to radiation from more
active stars, the transition to a regime of hydrodynamic escape from
the top of the atmosphere occurs at larger orbital distances. A greater
X-ray to EUV flux ratio in these stars compared with the solar case
also produces ionospheres that extend to lower altitudes and are
significantly more pronounced.
---------------------------------------------------------
Title: Planets and Stellar Activity: Hide and Seek in the CoRoT-7
system
Authors: Haywood, R. D.; Cameron, A. C.; Queloz, D.; Barros, S. C. C.;
Deleuil, M.; Fares, R.; Gillon, M.; Hatzes, A.; Lanza, A. F.; Lovis,
C.; Moutou, C.; Pepe, F.; Pollacco, D.; Santerne, A.; Ségransan,
D.; Unruh, Y.
2014IAUS..299..237H Altcode:
Since the discovery of the transiting Super-Earth CoRoT-7b, several
investigations have been made of the number and precise masses of
planets present in the system, but they all yield different results,
owing to the star's high level of activity. Radial velocity (RV)
variations induced by stellar activity therefore need to be modelled
and removed to allow a reliable detection of all planets in the
system. We re-observed CoRoT-7 in January 2012 with both HARPS and
the CoRoT satellite, so that we now have the benefit of simultaneous
RV and photometric data. We fitted the off-transit variations in
the CoRoT lightcurve using a harmonic decomposition similar to that
implemented in Queloz et al. (2009). This fit was then used to model
the stellar RV contribution, according to the methods described by
Aigrain et al. (2011). This model was incorporated into a Monte Carlo
Markov Chain in order to make a precise determination of the orbits
of CoRoT-7b and CoRoT-7c. We also assess the evidence for the presence
of one or two additional planetary companions.
---------------------------------------------------------
Title: VST Photometric H-alpha Survey of the Southern Galactic Plane
and Bulge (VPHAS+)
Authors: Drew, J. E.; Barentsen, G.; Fabregat, J.; Farnhill, H.;
Mohr-Smith, M.; Wright, N. J.; Gonzalez-Solares, E.; Irwin, M. J.;
Lewis, J.; Yoldas, A. K.; Greimel, R.; Eislöffel, J.; Groot, P.;
Barlow, M. J.; Corradi, R.; Gänsicke, B. T.; Knigge, C.; Mampaso,
A.; Morris, R.; Naylor, T.; Parker, Q. A.; Raddi, R.; Sale, S. E.;
Steeghs, D.; Unruh, Y. C.; Vink, J. S.; Walsh, J. R.; Walton, N. A.;
Wesson, R.; Zijlstra, A.
2013Msngr.154...41D Altcode:
The VST Photometric H-alpha survey of the Southern Galactic Plane and
Bulge (VPHAS+) is collecting single-epoch Sloan u, g, r, i and H-alpha
narrowband photometry, at arcsecond resolution, down to point-source
(Vega) magnitudes of ~ 21. The survey footprint encloses the entire
southern Galactic Plane within the Galactic latitude range -5° <
b < +5°, expanding to b = ±10° in the Galactic Bulge. This
brief description of VPHAS+ includes sample data and examples of early
science validation.
---------------------------------------------------------
Title: Hot-Jupiter ionospheres irradiated by low-mass stars
Authors: Chadney, J.; Galand, M.; Unruh, Y.; Koskinen, T.;
Sanz-Forcada, J.
2013EPSC....8..800C Altcode:
We present a modelling study of the upper atmospheres of extra-solar
planets, focussing on the influence of different stellar radiation
spectra on the composition and structure of the ionosphere around
a gas-giant planet. In particular, we concentrate on hot-Jupiter
planets orbiting low mass stars, of K and M type. Compared to a solar
type star, the XUV radiation of these stars is extremely variable and
they have a much higher XUV-to-bolometric-flux ratio than similarly
aged solar type stars - greatly affecting the planetary ionospheres
they irradiate. In this work, XUV spectra for the different stars
selected are constructed using a combination of spectral data from
various space telescopes, as well as coronal models of the stars. Ion
production rates and densities are then calculated for a given H2/H/He
background atmosphere, taking into account ionisation through both
primary and secondary processes. Additionally, the effect of orbital
separation on ionospheric composition is examined. Results show that
in atmospheres subjected to radiation from active M-dwarf stars,
ion production is boosted in the lower ionosphere, which is also the
region most affected by secondary ionisation processes.
---------------------------------------------------------
Title: Studying the Sun's radial velocity jitter to improve low-mass
exoplanet detections
Authors: Haywood, R. D.; Cameron, A. C.; Queloz, D.; Fares, R.; Llama,
J.; Deleuil, M.; Gillon, M.; Hatzes, A.; Lanza, A. F.; Lovis, C.;
Moutou, C.; Pepe, F.; Pollaco, D.; Ségransan, D.; Unruh, Y.
2013EPSC....8..215H Altcode:
One of the most common methods used to discover extra-solar planets is
to monitor a star's radial velocity (RV) in order to detect the reflex
orbital motion caused by one or more planets orbiting the star. When
looking for "small" planets (Neptune or Earth mass), the RV signals
induced by these planets are entangled with the jitter arising from
the star's magnetic activity. The Sun's activity is well known and it
is possible to remove all RV components induced by all other bodies of
the solar system. We have obtained its activity-driven RV variations
over two solar rotations using HARPS by observing sunlight reflected off
the bright asteroid Vesta. We aim to model the solar RV jitter in terms
of the continuum lightcurve, the chromospheric Ca II H&K emission,
and the line-profile distortions produced by spots drifting across the
face of the Sun. By using the "ground truth" of solar observations
in this way, we will identify photometric and spectroscopic proxies
that will make it possible to model and remove the stellar activity
RV contribution from exoplanet RV curves.
---------------------------------------------------------
Title: A Collaborative FP7 Effort towards the First European
Comprehensive SOLar Irradiance Data Exploitation (SOLID)
Authors: Haberreiter, Margit; Dasi, Maria; Delouille, Veronique; Del
Zanna, Giulio; Dudok de Wit, Thierry; Ermolli, Ilaria; Kretzschmar,
Matthieu; Krivova, Natalie; Mason, Helen; Qahwaji, Rami; Schmutz,
Werner; Solanki, Sami; Thuillier, Gerard; Tourpali, Kleareti; Unruh,
Yvonne; Verbeeck, Cis; Weber, Mark; Woods, Tom
2013EGUGA..1513079H Altcode:
Variations of solar irradiance are the most important natural factor
in the terrestrial climate and as such, the time dependent spectral
solar irradiance is a crucial input to any climate modelling. There
have been previous efforts to compile solar irradiance but it is
still uncertain by how much the spectral and total solar irradiance
changed on yearly, decadal and longer time scales. Observations of
irradiance data exist in numerous disperse data sets. Therefore, it
is important to bring together the European expertise in the field
to analyse and merge the complete set of European irradiance data,
complemented by archive data that include data from non-European
missions. We report on the initiation of a collaborative effort to unify
representatives from all European solar space experiments and European
teams specialized in multi-wavelength solar image processing. It is
intended to include the European groups involved in irradiance modelling
and reconstruction. They will work with two different state of the art
approaches to produce reconstructed spectral and total solar irradiance
data as a function of time. These results will be used to bridge
gaps in time and wavelength coverage of the observational data. This
will allow the proposing SOLID team to reduce the uncertainties in
the irradiance time series - an important requirement by the climate
community - and to provide uniform data sets of modelled and observed
solar irradiance data from the beginning of the space era to the
present including proper error and uncertainty estimates. Climate
research needs these data sets and therefore, the primary benefit
is for the climate community, but the stellar community, planetary,
lunar, and ionospheric researchers are also interested in having at
their disposition incident radiation of the Sun. The proposing team
plans to realize a wide international synergy in solar physics from
7 European countries, and collaborators from the US, complemented by
representatives from the climate community, who will accompany their
research work with wide dissemination activities.
---------------------------------------------------------
Title: Modeling the variability of Sun-like stars
Authors: Shapiro, Alexander; Knaack, Reto; Krivova, Natalie; Schmutz,
Werner; Solanki, Sami; Unruh, Yvonne
2013EGUGA..15.9981S Altcode:
We present a model which attributes the variability of the stellar
radiative energy flux to the imbalance between the contributions from
dark starspots and bright faculae. The stellar radiative energy flux
variations are modeled from the individual component's spectra, by
weighting them with corresponding filling factors. The filling factors
are deduced by extrapolating the sunspot and facular filling factors
dependencies on solar CaII S-index to stars with different levels
of the chromospheric activity. Our approach allows us to model the
stellar photometric variability vs. activity dependency and reproduce
the transition from spot-dominated to facula-dominated regimes of
variability. We show how the effect of inclination (arising due to the
random position of the Earth-bound observer relative to the directions
of stellar rotational axis) can affect these dependencies and present
the modeling of the individual stellar photometric light curves.
---------------------------------------------------------
Title: Recent variability of the solar spectral irradiance and its
impact on climate modelling
Authors: Ermolli, I.; Matthes, K.; Dudok de Wit, T.; Krivova,
N. A.; Tourpali, K.; Weber, M.; Unruh, Y. C.; Gray, L.; Langematz,
U.; Pilewskie, P.; Rozanov, E.; Schmutz, W.; Shapiro, A.; Solanki,
S. K.; Woods, T. N.
2013ACP....13.3945E Altcode: 2012ACPD...1224557E; 2013arXiv1303.5577E
The lack of long and reliable time series of solar spectral irradiance
(SSI) measurements makes an accurate quantification of solar
contributions to recent climate change difficult. Whereas earlier SSI
observations and models provided a qualitatively consistent picture of
the SSI variability, recent measurements by the SORCE (SOlar Radiation
and Climate Experiment) satellite suggest a significantly stronger
variability in the ultraviolet (UV) spectral range and changes in the
visible and near-infrared (NIR) bands in anti-phase with the solar
cycle. A number of recent chemistry-climate model (CCM) simulations
have shown that this might have significant implications on the
Earth's atmosphere. Motivated by these results, we summarize here
our current knowledge of SSI variability and its impact on Earth's
climate. <BR /><BR /> We present a detailed overview of existing SSI
measurements and provide thorough comparison of models available to
date. SSI changes influence the Earth's atmosphere, both directly,
through changes in shortwave (SW) heating and therefore, temperature
and ozone distributions in the stratosphere, and indirectly, through
dynamical feedbacks. We investigate these direct and indirect effects
using several state-of-the art CCM simulations forced with measured
and modelled SSI changes. A unique asset of this study is the use
of a common comprehensive approach for an issue that is usually
addressed separately by different communities. <BR /><BR /> We show
that the SORCE measurements are difficult to reconcile with earlier
observations and with SSI models. Of the five SSI models discussed
here, specifically NRLSSI (Naval Research Laboratory Solar Spectral
Irradiance), SATIRE-S (Spectral And Total Irradiance REconstructions
for the Satellite era), COSI (COde for Solar Irradiance), SRPM (Solar
Radiation Physical Modelling), and OAR (Osservatorio Astronomico di
Roma), only one shows a behaviour of the UV and visible irradiance
qualitatively resembling that of the recent SORCE measurements. However,
the integral of the SSI computed with this model over the entire
spectral range does not reproduce the measured cyclical changes of the
total solar irradiance, which is an essential requisite for realistic
evaluations of solar effects on the Earth's climate in CCMs. <BR /><BR
/> We show that within the range provided by the recent SSI observations
and semi-empirical models discussed here, the NRLSSI model and SORCE
observations represent the lower and upper limits in the magnitude
of the SSI solar cycle variation. <BR /><BR /> The results of the
CCM simulations, forced with the SSI solar cycle variations estimated
from the NRLSSI model and from SORCE measurements, show that the direct
solar response in the stratosphere is larger for the SORCE than for the
NRLSSI data. Correspondingly, larger UV forcing also leads to a larger
surface response. <BR /><BR /> Finally, we discuss the reliability
of the available data and we propose additional coordinated work,
first to build composite SSI data sets out of scattered observations
and to refine current SSI models, and second, to run coordinated
CCM experiments.
---------------------------------------------------------
Title: Solar and stellar spectral variability
Authors: Unruh, Yvonne; Ball, William
2013EGUGA..15.8414U Altcode:
Measurements of the changes in the solar spectral irradiance are
available for three solar cycles and there is a good understanding
of the irradiance changes on time scales ranging from a day to a few
years. Observing longer-term changes (tens of years and longer) is more
difficult, and there is much uncertainty regarding the Sun's long-term
behaviour. Stellar comparisons are often used to explore a wider range
of activity regimes and to estimate past and future solar variability
levels. At the same time, we want to find out how different the solar
example is and whether we can use it as a paradigm when finding and
characterising exoplanets around cool stars. We will discuss some of
the challenges that we encounter when comparing solar and stellar
variability, such as, e.g., the spread of stellar inclinations and
effective temperatures, and uncertainties in the relative area coverages
and contrasts of dark and bright features. Considering different levels
of spot and facular coverage for a range of effective temperatures,
we investigate the expected spectral variability and compare it to
observed solar and stellar variability.
---------------------------------------------------------
Title: Solar irradiance variability
Authors: Solanki, S. K.; Unruh, Y. C.
2013AN....334..145S Altcode: 2013csss...17..145S; 2012arXiv1210.5911S
The Sun has long been considered a constant star, to the extent
that its total irradiance was termed the solar constant. It required
radiometers in space to detect the small variations in solar irradiance
on timescales of the solar rotation and the solar cycle. A part of
the difficulty is that there are no other constant natural daytime
sources to which the Sun's brightness can be compared. The discovery
of solar irradiance variability rekindled a long-running discussion on
how strongly the Sun affects our climate. A non-negligible influence is
suggested by correlation studies between solar variability and climate
indicators. The mechanism for solar irradiance variations that fits
the observations best is that magnetic features at the solar surface,
i.e. sunspots, faculae and the magnetic network, are responsible for
almost all variations (although on short timescales convection and
p-mode oscillations also contribute). In spite of significant progress
important questions are still open. Thus there is a debate on how
strongly irradiance varies on timescales of centuries (i.e. how much
darker the Sun was during the Maunder minimum than it is today). It is
also not clear how the solar spectrum changes over the solar cycle. Both
these questions are of fundamental importance for working out just how
strongly the Sun influences our climate. Another interesting question
is how solar irradiance variability compares with that of other cool
dwarfs, particularly now that observations from space are available
also for stars.
---------------------------------------------------------
Title: Ionisation of gas-giant type exoplanetary atmospheres under
stellar radiation
Authors: Chadney, J.; Galand, M.; Unruh, Y.; Koskinen, T.
2012epsc.conf..474C Altcode: 2012espc.conf..474C
Characterising extra-solar planetary atmospheres is the new frontier
in exoplanetary research. Future space-based missions will provide
consistent and stable measurements of star systems with known transiting
exoplanets. These missions, that are currently at selection stage,
are ESA's Exoplanet Characterisation Observatory (EChO) and NASA's Fast
INfrared Exoplanet Spectroscopy Survey Explorer (FINESSE). Once up and
running, they will deliver high stability, long duration observations
in the visible to midinfrared. In the meantime, modelling studies of
the atmospheres of extra-solar planets, such as the one undertaken
in this work, will be useful to help plan the observational process
and provide insight into the data analysis and interpretation, after
the missions are launched. The purpose of this work is to study the
influence of differing stellar radiation profiles on the composition and
structure of an ionosphere around a typical gas-giant planet. Particular
interest is focused upon M and K-type dwarf stars. Typical XUV spectra
for the different star types are constructed by combining data from
various satellites. Unobserved parts of the spectrum are filled
using a combination of extrapolation and results from a correlation
study of the solar spectrum. The constructed spectra are then used
to calculate ion densities, produced through photo-ionisation, in a
H2/H/He atmosphere, considering the neutral atmosphere as a constant
background. Preliminary results show that in planets irradiated
by K-type stars, photo-ionisation production rates are remarkably
similar to those in planets orbiting Sun-like stars. The case of
atmospheres subjected to radiation from flaring Mstars is altogether
more interesting: an extension of the production rate peak towards
lower altitudes is predicted.
---------------------------------------------------------
Title: Solar Irradiance Models and Measurements: A Comparison in
the 220-240 nm wavelength band
Authors: Unruh, Yvonne C.; Ball, Will T.; Krivova, Natalie A.
2012SGeo...33..475U Altcode: 2011arXiv1111.2068U; 2011SGeo..tmp..121U
Solar irradiance models that assume solar irradiance variations
to be due to changes in the solar surface magnetic flux have been
successfully used to reconstruct total solar irradiance on rotational
as well as cyclical and secular time scales. Modelling spectral solar
irradiance is not yet as advanced, and also suffers from a lack of
comparison data, in particular on solar cycle time scales. Here,
we compare solar irradiance in the 220-240 nm band as modelled
with SATIRE-S and measured by different instruments on the UARS
and SORCE satellites. We find good agreement between the model and
measurements on rotational time scales. The long-term trends, however,
show significant differences. Both SORCE instruments, in particular,
show a much steeper gradient over the decaying part of cycle 23 than
the modelled irradiance or that measured by UARS/SUSIM.
---------------------------------------------------------
Title: Reconstruction of total solar irradiance 1974-2009
Authors: Ball, W. T.; Unruh, Y. C.; Krivova, N. A.; Solanki, S.;
Wenzler, T.; Mortlock, D. J.; Jaffe, A. H.
2012A&A...541A..27B Altcode: 2012arXiv1202.3554B
Context. The study of variations in total solar irradiance (TSI)
is important for understanding how the Sun affects the Earth's
climate. <BR /> Aims: Full-disk continuum images and magnetograms are
now available for three full solar cycles. We investigate how modelled
TSI compares with direct observations by building a consistent modelled
TSI dataset. The model, based only on changes in the photospheric
magnetic flux can then be tested on rotational, cyclical and secular
timescales. <BR /> Methods: We use Kitt Peak and SoHO/MDI continuum
images and magnetograms in the SATIRE-S model to reconstruct TSI over
cycles 21-23. To maximise independence from TSI composites, SORCE/TIM
TSI data are used to fix the one free parameter of the model. We compare
and combine the separate data sources for the model to estimate an
uncertainty on the reconstruction and prevent any additional free
parameters entering the model. <BR /> Results: The reconstruction
supports the PMOD composite as being the best historical record of
TSI observations, although on timescales of the solar rotation the
IRMB composite provides somewhat better agreement. Further to this,
the model is able to account for 92% of TSI variations from 1978
to 2009 in the PMOD composite and over 96% during cycle 23. The
reconstruction also displays an inter-cycle, secular decline of
0.20<SUP>+0.12</SUP><SUB>-0.09</SUB> W m<SUP>-2</SUP> between cycle
23 minima, in agreement with the PMOD composite. <BR /> Conclusions:
SATIRE-S is able to recreate TSI observations on all timescales of a
day and longer over 31 years from 1978. This is strong evidence that
changes in photospheric magnetic flux alone are responsible for almost
all solar irradiance variations over the last three solar cycles.
---------------------------------------------------------
Title: Solar Irradiance Models and Measurements: A Comparison in
the 220–240 nm wavelength band
Authors: Unruh, Yvonne C.; Ball, Will T.; Krivova, Natalie A.
2012omee.book..143U Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The large-scale magnetic field and poleward mass accretion
of the classical T Tauri star TW Hya
Authors: Donati, J. -F.; Gregory, S. G.; Alencar, S. H. P.; Bouvier,
J.; Hussain, G.; Skelly, M.; Dougados, C.; Jardine, M. M.; Ménard,
F.; Romanova, M. M.; Unruh, Y. C.
2011MNRAS.417..472D Altcode: 2011arXiv1106.4162D; 2011MNRAS.tmp.1284D
We report here results of spectropolarimetric observations of the
≃8 Myr classical T Tauri star (cTTS) TW Hya carried out with
ESPaDOnS at the Canada-France-Hawaii Telescope in the framework of
the 'Magnetic Protostars and Planets' programme, and obtained at
two different epochs (2008 March and 2010 March). Obvious Zeeman
signatures are detected at all times, both in photospheric lines and
in accretion-powered emission lines. Significant intrinsic variability
and moderate rotational modulation are observed in both photospheric
and accretion proxies. <P />Using tomographic imaging, we reconstruct
maps of the large-scale field of the photospheric brightness and the
accretion-powered emission at the surface of TW Hya at both epochs. We
find that the magnetic topology is mostly poloidal and axisymmetric
with respect to the rotation axis of the star and that the octupolar
component of the large-scale field (2.5-2.8 kG at the pole) largely
dominates the dipolar component. This large-scale field topology is
characteristic of partly convective stars, supporting the conclusion
(from evolutionary models) that TW Hya already hosts a radiative
core. We also show that TW Hya features a high-latitude photospheric
cool spot overlapping with the main magnetic pole (and producing the
observed radial velocity fluctuations); this is also where accretion
concentrates most of the time, although accretion at lower latitudes
is found to occur episodically. <P />We propose that the relatively
rapid rotation of TW Hya (with respect to AA Tau-like cTTSs) directly
reflects the weakness of the large-scale dipole, no longer capable of
magnetically disrupting the accretion disc up to the corotation radius
(at which the Keplerian period equals the stellar rotation period). We
therefore conclude that TW Hya is in a phase of rapid spin-up as its
large-scale dipole field progressively vanishes.
---------------------------------------------------------
Title: Solar irradiance variability: a six-year comparison between
SORCE observations and the SATIRE model
Authors: Ball, W. T.; Unruh, Y. C.; Krivova, N. A.; Solanki, S.;
Harder, J. W.
2011A&A...530A..71B Altcode: 2011arXiv1104.0885B
<BR /> Aims: We investigate how well modeled solar irradiances agree
with measurements from the SORCE satellite, both for total solar
irradiance and broken down into spectral regions on timescales of
several years. <BR /> Methods: We use the SATIRE model and compare
modeled total solar irradiance (TSI) with TSI measurements over the
period 25 February 2003 to 1 November 2009. Spectral solar irradiance
over 200-1630 nm is compared with the SIM instrument on SORCE over
the period 21 April 2004 to 1 November 2009. We discuss the overall
change in flux and the rotational and long-term trends during this
period of decline from moderate activity to the recent solar minimum
in ~10 nm bands and for three spectral regions of significant interest:
the UV integrated over 200-300 nm, the visible over 400-691 nm and the
IR between 972-1630 nm. <BR /> Results: The model captures 97% of the
observed TSI variation. This is on the order at which TSI detectors
agree with each other during the period considered. In the spectral
comparison, rotational variability is well reproduced, especially
between 400 and 1200 nm. The magnitude of change in the long-term
trends is many times larger in SIM at almost all wavelengths while
trends in SIM oppose SATIRE in the visible between 500 and 700 nm and
again between 1000 and 1200 nm. We discuss the remaining issues with
both SIM data and the identified limits of the model, particularly
with the way facular contributions are dealt with, the limit of flux
identification in MDI magnetograms during solar minimum and the model
atmospheres in the IR employed by SATIRE. However, it is unlikely that
improvements in these areas will significantly enhance the agreement
in the long-term trends. This disagreement implies that some mechanism
other than surface magnetism is causing SSI variations, in particular
between 2004 and 2006, if the SIM data are correct. Since SATIRE
was able to reproduce UV irradiance between 1991 and 2002 from UARS,
either the solar mechanism for SSI variation fundamentally changed
around the peak of cycle 23, or there is an inconsistency between UARS
and SORCE UV measurements. We favour the second explanation.
---------------------------------------------------------
Title: Intensity contrast from MHD simulations and HINODE observations
Authors: Afram, N.; Unruh, Y. C.; Solanki, S. K.; Schüssler, M.;
Lagg, A.; Vögler, A.
2011A&A...526A.120A Altcode: 2010arXiv1011.6102A
Context. Changes in the solar surface area, which is covered by
small-scale magnetic elements, are thought to cause long-term changes
in the solar spectral irradiance, which are important for determining
the impact on Earth's climate. <BR /> Aims: To study the effect of
small-scale magnetic elements on the total and spectral irradiance,
we derive their contrasts from 3-D MHD simulations of the solar
atmosphere. These calculations are necessary because measurements of
small-scale flux tube contrasts are confined to a few wavelengths and
affected by scattered light and instrument defocus, even for space
observations. <BR /> Methods: To test the contrast calculations,
we compare rms contrasts from simulations with those obtained with
the broad-band filter imager mounted on the Solar Optical Telescope
(SOT) onboard the Hinode satellite and also analyse centre-to-limb
variations (CLV). The 3-D MHD simulations include the interaction
between convection and magnetic flux tubes. They are performed by
assuming non-grey radiative transfer and using the MURaM code. The
simulations have an average vertical magnetic field of 0 G, 50 G, and
200 G. Emergent intensities are calculated with the spectral synthesis
code ATLAS9 and are convolved with a theoretical point-spread function
to account for the properties of the observations' optical system. <BR
/> Results: We find reasonable agreement between simulated and observed
intensity distributions in the visible continuum bands. Agreement is
poorer for the CN and G-bands. The analysis of the simulations uncovers
a potentially more realistic centre-to-limb behaviour than calculations
based on 1-D model atmospheres. <BR /> Conclusions: We conclude that
starting from 3-D MHD simulations represents a powerful approach
to obtaining intensity contrasts for a wide wavelength coverage and
different positions across on the solar disk. This also paves the way
for future calculations of facular and network contrast as a function
of magnetic fluxes.
---------------------------------------------------------
Title: Towards a long-term record of solar total and spectral
irradiance
Authors: Krivova, N. A.; Solanki, S. K.; Unruh, Y. C.
2011JASTP..73..223K Altcode: 2009arXiv0911.4002K
The variation of total solar irradiance (TSI) has been measured since
1978 and that of the spectral irradiance for an even shorter amount of
time. Semi-empirical models are now available that reproduce over 80%
of the measured irradiance variations. An extension of these models into
the more distant past is needed in order to serve as input to climate
simulations. Here we review our most recent efforts to model solar
total and spectral irradiance on time scales from days to centuries and
even longer. Solar spectral irradiance has been reconstructed since
1947. Reconstruction of solar total irradiance goes back to 1610 and
suggests a value of about 1-1.5W/m<SUP>2</SUP> for the increase in
the cycle-averaged TSI since the end of the Maunder minimum, which
is significantly lower than previously assumed but agrees with other
modern models. First steps have also been made towards reconstructions
of solar total and spectral irradiance on time scales of millennia.
---------------------------------------------------------
Title: Magnetospheric accretion and spin-down of the prototypical
classical T Tauri star AA Tau
Authors: Donati, J. -F.; Skelly, M. B.; Bouvier, J.; Gregory,
S. G.; Grankin, K. N.; Jardine, M. M.; Hussain, G. A. J.; Ménard,
F.; Dougados, C.; Unruh, Y.; Mohanty, S.; Aurière, M.; Morin, J.;
Farès, R.; MAPP Collaboration
2010MNRAS.409.1347D Altcode: 2010arXiv1007.4407D; 2010MNRAS.tmp.1622D
From observations collected with the ESPaDOnS spectropolarimeter
at the Canada-France-Hawaii Telescope (CFHT) and with the NARVAL
spectropolarimeter at the Télescope Bernard Lyot (TBL), we report the
detection of Zeeman signatures on the prototypical classical T Tauri
star AA Tau, both in photospheric lines and accretion-powered emission
lines. Using time series of unpolarized and circularly polarized
spectra, we reconstruct at two epochs maps of the magnetic field,
surface brightness and accretion-powered emission of AA Tau. We find
that AA Tau hosts a 2-3 kG magnetic dipole tilted at ≃20° to the
rotation axis, and of presumably dynamo origin. We also show that the
magnetic poles of AA Tau host large cool spots at photospheric level
and accretion regions at chromospheric level. <P />The accretion rate
at the surface of AA Tau at the time of our observations (estimated
from the emission in the He I D<SUB>3</SUB> line mainly) is strongly
variable, ranging from -9.6 to -8.5 and equal to -9.2 in average (in
logarithmic scale and in M<SUB>⊙</SUB> yr<SUP>-1</SUP>); this is
an order of magnitude smaller than the disc accretion rate at which
the magnetic truncation radius (below which the disc is disrupted by
the stellar magnetic field) matches the corotation radius (where the
Keplerian period equals the stellar rotation period) - a necessary
condition for accretion to occur. It suggests that AA Tau is largely
in the propeller regime, with most of the accreting material in the
inner disc regions being expelled outwards and only a small fraction
accreted towards the surface of the star. The strong variability in
the observed surface mass accretion rate and the systematic time-lag
of optical occultations (by the warped accretion disc) with respect
to magnetic and accretion-powered emission maxima also support this
conclusion. <P />Our results imply that AA Tau is being actively
spun-down by the star/disc magnetic coupling and appears as an ideal
laboratory for studying angular momentum losses of forming suns in
the propeller regime.
---------------------------------------------------------
Title: IPHAS A-type Stars with Mid-IR Excesses in Spitzer Surveys
Authors: Hales, Antonio S.; Barlow, Michael J.; Drew, Janet E.; Unruh,
Yvonne C.; Greimel, Robert; Irwin, Michael J.; González-Solares,
Eduardo
2010HiA....15..815H Altcode:
The Isaac Newton Photometric H-Alpha Survey (IPHAS) provides
(r‧-Hα)-(r‧-i‧) colors, which can be used to select AV0-5 Main
Sequence star candidates (age~20-200 Myr). By combining a sample of
23050 IPHAS-selected A-type stars with 2MASS, GLIMPSE and MIPSGAL
photometry we searched for mid-infrared excesses attributable to dusty
circumstellar disks. Positional cross-correlation yielded a sample of
2692 A-type stars, of which 0.6% were found to have 8-μm excesses above
the expected photospheric values. The low fraction of main sequence
stars with mid-IR excesses found in this work indicates that dust
disks in the terrestrial planet zone of Main Sequence intermediate mass
stars are rare. Dissipation mechanisms such as photo-evaporation, grain
growth, collisional grinding or planet formation could possibly explain
the depletion of dust detected in the inner regions of these disks.
---------------------------------------------------------
Title: Quiet-sun Intensity Contrasts in the Near-ultraviolet as
Measured from SUNRISE
Authors: Hirzberger, J.; Feller, A.; Riethmüller, T. L.; Schüssler,
M.; Borrero, J. M.; Afram, N.; Unruh, Y. C.; Berdyugina, S. V.;
Gandorfer, A.; Solanki, S. K.; Barthol, P.; Bonet, J. A.; Martínez
Pillet, V.; Berkefeld, T.; Knölker, M.; Schmidt, W.; Title, A. M.
2010ApJ...723L.154H Altcode:
We present high-resolution images of the Sun in the near-ultraviolet
spectral range between 214 nm and 397 nm as obtained from the first
science flight of the 1 m SUNRISE balloon-borne solar telescope. The
quiet-Sun rms intensity contrasts found in this wavelength range are
among the highest values ever obtained for quiet-Sun solar surface
structures—up to 32.8% at a wavelength of 214 nm. We compare the
rms contrasts obtained from the observational data with theoretical
intensity contrasts obtained from numerical magnetohydrodynamic
simulations. For 388 nm and 312 nm the observations agree well with
the numerical simulations whereas at shorter wavelengths discrepancies
between observed and simulated contrasts remain.
---------------------------------------------------------
Title: Quiet-Sun intensity contrasts in the near ultraviolet
Authors: Hirzberger, Johann; Feller, Alex; Riethmüller, Tino L.;
Schüssler, Manfred; Borrero, Juan M.; Afram, Nadine; Unruh, Yvonne C.;
Berdyugina, Svetlana V.; Gandorfer, Achim; Solanki, Sami K.; Barthol,
Peter; Bonet, Jose A.; Martínez Pillet, Valentin; Berkefeld, Thomas;
Knölker, Michael; Schmidt, Wolfgang; Title, Alan M.
2010arXiv1009.1050H Altcode:
We present high-resolution images of the Sun in the near ultraviolet
spectral range between 214 nm and 397 nm as obtained from the first
science flight of the 1-m Sunrise balloon-borne solar telescope. The
quiet-Sun rms intensity contrasts found in this wavelength range
are among the highest values ever obtained for quiet-Sun solar
surface structures - up to 32.8% at a wavelength of 214 nm. We
compare with theoretical intensity contrasts obtained from numerical
magneto-hydrodynamic simulations. For 388 nm and 312 nm the observations
agree well with the numerical simulations whereas at shorter wavelengths
discrepancies between observed and simulated contrasts remain.
---------------------------------------------------------
Title: Dynamo processes in the T Tauri star V410 Tau
Authors: Skelly, M. B.; Donati, J. -F.; Bouvier, J.; Grankin, K. N.;
Unruh, Y. C.; Artemenko, S. A.; Petrov, P.
2010MNRAS.403..159S Altcode: 2009arXiv0911.5476S; 2010MNRAS.tmp..187S
We present new brightness and magnetic images of the weak-line T Tauri
star V410 Tau, made by using data from the Narval spectropolarimeter at
Télescope Bernard Lyot (TBL). The brightness image shows a large polar
spot and significant spot coverage at lower latitudes. The magnetic maps
show a field that is predominantly dipolar and non-axisymmetric with a
strong azimuthal component. The field is 50 per cent poloidal and 50
per cent toroidal, and very little differential rotation is apparent
from the magnetic images. <P />A photometric monitoring campaign on this
star has previously revealed V-band variability of up to 0.6 mag, but in
2009 the light curve is much flatter. The Doppler image presented here
is consistent with this low variability. Calculating the flux predicted
by the mapped spot distribution gives a peak-to-peak variability of
0.04 mag. The reduction in the amplitude of the light curve, compared
with previous observations, appears to be related to a change in the
distribution of the spots rather than the number or area. <P />This
paper is the first from a Zeeman-Doppler imaging campaign being carried
out on V410 Tau between 2009 and 2012 at the TBL. During this time,
it is expected that the light curve will return to a high-amplitude
state, allowing us to ascertain whether the photometric changes are
accompanied by a change in the magnetic field topology. <P />Based on
observations obtained at the Télescope Bernard Lyot (TBL), operated
by Centre national de la recherche scientifique/Institut national des
sciences de l'Univers (CNRS/INSU) <P />E-mail: mskelly@ast.obs-mip.fr
---------------------------------------------------------
Title: Complex magnetic topology and strong differential rotation
on the low-mass T Tauri star V2247 Oph
Authors: Donati, J. -F.; Skelly, M. B.; Bouvier, J.; Jardine, M. M.;
Gregory, S. G.; Morin, J.; Hussain, G. A. J.; Dougados, C.; Ménard,
F.; Unruh, Y.
2010MNRAS.402.1426D Altcode: 2009arXiv0911.1080D; 2009MNRAS.tmp.1895D
From observations collected with the ESPaDOnS spectropolarimeter
at the Canada-France-Hawaii Telescope, we report the detection of
Zeeman signatures on the low-mass classical T Tauri star (cTTS) V2247
Oph. Profile distortions and circular polarization signatures detected
in photospheric lines can be interpreted as caused by cool spots and
magnetic regions at the surface of the star. The large-scale field
is of moderate strength and highly complex; moreover, both the spot
distribution and the magnetic field show significant variability on a
time-scale of only 1 week, as a likely result of strong differential
rotation. Both properties make V2247 Oph very different from the (more
massive) prototypical cTTS BP Tau; we speculate that this difference
reflects the lower mass of V2247 Oph. <P />During our observations,
V2247 Oph was in a low-accretion state, with emission lines showing
only weak levels of circular polarization; we nevertheless find that
excess emission apparently concentrates in a mid-latitude region of a
strong radial field, suggesting that it is the footpoint of an accretion
funnel. <P />The weaker and more complex field that we report on V2247
Oph may share similarities with those of very-low-mass late-M dwarfs
and potentially explain why low-mass cTTSs rotate on average faster
than intermediate-mass ones. These surprising results need confirmation
from new independent data sets on V2247 Oph and other similar low-mass
cTTSs. <P />Based on observations obtained at the Canada-France-Hawaii
Telescope, operated by the National Research Council of Canada, the
Institut National des Sciences de l'Univers of the Centre National de
la Recherche Scientifique of France and the University of Hawaii. <P
/>E-mail: donati@ast.obs-mip.fr (J-FD); mskelly@ast.obs-mip.fr
(MBS); jerome.bouvier@obs.ujf-grenoble.fr (JB); mmj@st-andrews.ac.uk
(MMJ); sg64@st-andrews.ac.uk (SGG); jmorin@ast.obs-mip.fr (JM);
ghussain@eso.org (GAJH); catherine.dougados@obs.ujf-grenoble.fr (CD);
francois.menard@obs.ujf-grenoble.fr (FM); y.unruh@imperial.ac.uk (YU)
---------------------------------------------------------
Title: VizieR Online Data Catalog: Simulated UVEX colors with
reddening (Groot+, 2009)
Authors: Groot, P. J.; Verbeek, K.; Greimel, R.; Irwin, M.;
Gonzalez-Solares, E.; Gansicke, B. T.; de Groot, E.; Drew, J.;
Augusteijn, T.; Aungwerojwit, A.; Barlow, M.; Barros, S.; van den
Besselaar, E. J. M.; Casares, J.; Corradi, R.; Corral-Santana, J. M.;
Deacon, N.; van Ham, W.; Hu, H.; Heber, U.; Jonker, P. G.; King, R.;
Knigge, C.; Mampaso, A.; Marsh, T. R.; Morales-Rueda, L.; Napiwotzki,
R.; Naylor, T.; Nelemans, G.; Oosting, T.; Pyrzas, S.; Pretorius,
M.; Rodriguez-Gil, P.; Roelofs, G. H. A.; Sale, S.; Schellart, P.;
Steeghs, D.; Szyszka, C.; Unruh, Y.; Walton, N. A.; Weston, S.;
Witham, A.; Woudt, P.; Zijlstra, A.
2010yCat..73990323G Altcode:
To interpret the UVEX observations, simulations of the colours of stars
and the effect of reddening are a very powerful and important tool. In
obtaining the simulated colours, we follow the procedure as outlined
in Drew et al. (2005MNRAS.362..753D) for the IPHAS. <P />(6 data files).
---------------------------------------------------------
Title: A comparison of measured and simulated solar network contrast
Authors: Afram, N.; Unruh, Y. C.; Solanki, S. K.; Schüssler, M.;
Mathew, S. K.
2010IAUS..264...63A Altcode: 2009arXiv0910.0976A
Long-term trends in the solar spectral irradiance are important to
determine the impact on Earth's climate. These long-term changes are
thought to be caused mainly by changes in the surface area covered by
small-scale magnetic elements. The direct measurement of the contrast
to determine the impact of these small-scale magnetic elements
is, however, limited to a few wavelengths, and is, even for space
instruments, affected by scattered light and instrument defocus. In
this work we calculate emergent intensities from 3-D simulations of
solar magneto-convection and validate the outcome by comparing with
observations from Hinode/SOT. In this manner we aim to construct the
contrast at wavelengths ranging from the NUV to the FIR.
---------------------------------------------------------
Title: The structure of the outer Galactic disc as revealed by IPHAS
early A stars
Authors: Sale, S. E.; Drew, J. E.; Knigge, C.; Zijlstra, A. A.; Irwin,
M. J.; Morris, R. A. H.; Phillipps, S.; Drake, J. J.; Greimel, R.;
Unruh, Y. C.; Groot, P. J.; Mampaso, A.; Walton, N. A.
2010MNRAS.402..713S Altcode: 2009arXiv0909.3857S; 2009MNRAS.tmp.1816S
This study is an investigation of the stellar density profile of the
Galactic disc in the anticentre direction. We select over 40000 early
A stars from INT/WFC Photometric Hα Survey of the Northern Galactic
Plane (IPHAS) photometry in the Galactic longitude range 160° <
l < 200° close to the equatorial plane (-1° < b < +1°). We
then compare their observed reddening-corrected apparent magnitude
distribution with simulated photometry obtained from parametrized
models in order to set constraints on the anticentre stellar density
profile. By selecting A stars, we are appraising the properties of a
population only ~100 Myr old. We find that the stellar density profile
of young stars is well fit to an exponential with length-scale of (3020
+/- 120<SUB>statistical</SUB> +/- 180<SUB>systematic</SUB>) pc, which is
comparable to that obtained in earlier studies, out to a Galactocentric
radius of R<SUB>T</SUB> = (13.0 +/- 0.5<SUB>statistical</SUB> +/-
0.6<SUB>systematic</SUB>) kpc. At larger radii, the rate of decline
appears to increase with the scalelength dropping to (1200 +/-
300<SUB>statistical</SUB> +/- 70<SUB>systematic</SUB>) pc. This result
amounts to a refinement of the conclusions reached in previous studies
that the stellar density profile is abruptly truncated. The IPHAS A
star data are not compatible with models that propose a sudden change
in metallicity at R<SUB>G</SUB> = 10 kpc.
---------------------------------------------------------
Title: IPHAS and the symbiotic stars . II. New discoveries and a
sample of the most common mimics
Authors: Corradi, R. L. M.; Valentini, M.; Munari, U.; Drew, J. E.;
Rodríguez-Flores, E. R.; Viironen, K.; Greimel, R.; Santander-García,
M.; Sabin, L.; Mampaso, A.; Parker, Q.; DePew, K.; Sale, S. E.; Unruh,
Y. C.; Vink, J. S.; Rodríguez-Gil, P.; Barlow, M. J.; Lennon, D. J.;
Groot, P. J.; Giammanco, C.; Zijlstra, A. A.; Walton, N. A.
2010A&A...509A..41C Altcode: 2009arXiv0910.5930C
Context. Knowledge of the total population of symbiotic stars in
the Galaxy is important for understanding basic aspects of stellar
evolution in interacting binaries and the relevance of this class
of objects in the formation of supernovae of type Ia. <BR /> Aims:
In a previous paper, we presented the selection criteria needed to
search for symbiotic stars in IPHAS, the INT Hα survey of the Northern
Galactic plane. IPHAS gives us the opportunity to make a systematic,
complete search for symbiotic stars in a magnitude-limited volume. <BR
/> Methods: Follow-up spectroscopy at different telescopes worldwide
of a sample of sixty two symbiotic star candidates is presented. <BR
/> Results: Seven out of nineteen S-type candidates observed
spectroscopically are confirmed to be genuine symbiotic stars. The
spectral type of their red giant components, as well as reddening
and distance, were computed by modelling the spectra. Only one new
D-type symbiotic system, out of forty-three candidates observed,
was found. This was as expected (see discussion in our paper on the
selection criteria). The object shows evidence for a high density
outflow expanding at a speed ≥65 km s<SUP>-1</SUP>. Most of the
other candidates are lightly reddened classical T Tauri stars and
more highly reddened young stellar objects that may be either more
massive young stars of HAeBe type or classical Be stars. In addition,
a few notable objects have been found, such as three new Wolf-Rayet
stars and two relatively high-luminosity evolved massive stars. We also
found a helium-rich source, possibly a dense ejecta hiding a WR star,
which is surrounded by a large ionized nebula. <BR /> Conclusions:
These spectroscopic data allow us to refine the selection criteria for
symbiotic stars in the IPHAS survey and, more generally, to better
understand the behaviour of different Hα emitters in the IPHAS and
2MASS colour-colour diagrams. <P />Based on observations obtained at;
the 2.6 m Nordic Optical Telescope operated by NOTSA; the 2.5 m INT
and 4.2 m WHT telescopes of the Isaac Newton Group of Telescopes in
the Spanish Observatorio del Roque de Los Muchachos of the Instituto
de Astrofísica de Canarias; the 2.3 m ANU telescope at Siding Spring
Observatory, Australia; the Asiago 1.82 m telescope of the INAF
Astronomical Observatory of Padova, Italy; and the 2.1 m telescope
at San Pedro Martir, Mexico. Some of the INT spectra incorporated
into this paper were obtained as part of a CCI International Time
Programme awarded to the IPHAS collaboration. This publication makes
use of data products from the Two Micron All Sky Survey, which is
a joint project of the University of Massachusetts and the Infrared
Processing and Analysis Center/California Institute of Technology,
funded by the National Aeronautics and Space Administration and the
National Science Foundation. This research has also made use of the
SIMBAD database, operated at CDS, Strasbourg, France.
---------------------------------------------------------
Title: Modelling rotational and cyclical spectral solar irradiance
variations
Authors: Unruh, Yvonne
2010cosp...38...18U Altcode: 2010cosp.meet...18U
Solar irradiance changes are highly wavelength dependent: solar-cycle
variations in the UV can be on the order of tens of percent, while
changes in the visible are typically only of the order of one or two
permille. With the launch of a number of instruments to measure spectral
solar irradiance, we are now for a first time in a good position to
explore the changing solar irradiance over a large range of wavelengths
and to test our irradiance models as well as some of their underlying
assumptions. I will introduce some of the current modelling approaches
and present model-data comparisons, using the SATIRE irradiance
model and SORCE/SIM measurements as an example. I will conclude by
highlighting a number of outstanding questions regarding the modelling
of spectral irradiance and current approaches to address these.
---------------------------------------------------------
Title: Total and spectral irradiance comparisons between SIM and
the SATIRE model in the declining phase of cycle 23
Authors: Ball, Will; Unruh, Yvonne; Krivova, Natalie; Solanki, Sami
K.; Harder, Jerald
2010cosp...38..136B Altcode: 2010cosp.meet..136B
Climate models rely on accurate total and spectral solar irradiance
inputs, but until 2003 con-tinuous spectral irradiance information
across a large portion of the solar spectrum was lacking. Since the
launch of the Solar Radiation and Climate Experiment (SORCE), with the
Spectral Irradiance Monitor (SIM) observing the UV, visible and IR,
data have been accumulating and now cover a significant portion of
a cycle. For the first time this allows spectral models to be tested
over periods greater than a solar rotation. We present six years of
total and spectral irradiance reconstructions using the SATIRE model
that incorporates SOHO/MDI continuum and magnetogram images for the
period April 2004 to November 2009 in the declining phase of cycle 23
and through the recent unusual minimum. We compare these results with
the SIM instrument and so cover the spectral region 200 -1600 nm. While
detrended, short-term, variation is recreated well by the model, there
are discrepancies in longer-term trends between observations and the
model. This may become important when considering the radiative forcing
from the Sun used in climate research and so understanding why there is
such a significant disagreement is an important area of investigation.
---------------------------------------------------------
Title: Near-IR spectra of IPHAS extremely red Galactic AGB stars
Authors: Wright, N. J.; Barlow, M. J.; Greimel, R.; Drew, J. E.;
Matsuura, M.; Unruh, Y. C.; Zijlstra, A. A.
2009MNRAS.400.1413W Altcode: 2009arXiv0909.2642W; 2009MNRAS.tmp.1324W
We present a library of 139 near-IR spectra of cool asymptotic giant
branch stars that will be useful for comparison with theoretical
model atmosphere calculations and for modelling the integrated
emission from intermediate-age stellar populations. The source list
was selected from the `extremely red' region of the Isaac Newton
Telescope (INT) Photometric Hα Survey (IPHAS) colour-colour plane
that is overwhelmingly dominated by very late-type stars. The spectral
library also includes a large fraction of S-type and carbon stars. We
present a number of spectral classification sequences highlighting
the various molecular features identified and discuss a number of
rare features with uncertain identifications in the literature. With
its focus on particularly cool photospheres, this catalogue serves
as a companion to recent spectroscopic atlases of MK standards in the
near-IR. Finally, the relationship between IPHAS (r' - i') and (r' -
Hα) colours and spectroscopically determined properties is discussed
and a strong correlation between the (r' - Hα) colour and the C/O
abundance index for S-type and carbon stars is noted. This relation
has the potential to separate O-rich, S-type and carbon stars in the
Galaxy based on their photometry alone.
---------------------------------------------------------
Title: Doppler images and chromospheric variability of TWA 17
Authors: Skelly, M. B.; Unruh, Y. C.; Barnes, J. R.; Lawson, W. A.;
Donati, J. -F.; Collier Cameron, A.
2009MNRAS.399.1829S Altcode: 2009arXiv0907.2777S
We present Doppler imaging and a Balmer line analysis of the
weak-line T Tauri star TWA 17. Spectra were taken in 2006 with the
University College London Echelle Spectrograph on the Anglo-Australian
Telescope. Using least-squares deconvolution to improve the effective
signal-to-noise ratio, we produced a Doppler map of the surface spot
distribution. This shows similar features to maps of other rapidly
rotating T Tauri stars, i.e. a polar spot with more spots extending
out of it down to the equator. <P />In addition to the photospheric
variability, the chromospheric variability was studied using the Balmer
emission. The mean Hα profile has a narrow component consistent with
rotational broadening and a broad component extending out to 220 km
s<SUP>-1</SUP>. The variability in Hα suggests that the chromosphere
has at least one slingshot prominence 3R<SUB>*</SUB> above the surface.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Near-IR spectra of extremely red
AGB stars (Wright+, 2009)
Authors: Wright, N. J.; Barlow, M. J.; Greimel, R.; Drew, J. E.;
Matsuura, M.; Unruh, Y. C.; Zijlstra, A. A.
2009yCat..74001413W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The UV-Excess survey of the northern Galactic plane
Authors: Groot, Paul J.; Verbeek, Kars; Greimel, Robert; Irwin, Mike;
González-Solares, Eduardo; Gänsicke, Boris T.; de Groot, Eelco;
Drew, Janet; Augusteijn, Thomas; Aungwerojwit, Amornrat; Barlow,
Mike; Barros, Susana; van den Besselaar, Else J. M.; Casares, Jorge;
Corradi, Romano; Corral-Santana, Jesús M.; Deacon, Niall; van Ham,
Wilbert; Hu, Haili; Heber, Uli; Jonker, Peter G.; King, Rob; Knigge,
Christian; Mampaso, Antonio; Marsh, Tom R.; Morales-Rueda, Luisa;
Napiwotzki, Ralf; Naylor, Tim; Nelemans, Gijs; Oosting, Tim; Pyrzas,
Stylianos; Pretorius, Magaretha; Rodríguez-Gil, Pablo; Roelofs,
Gijs H. A.; Sale, Stuart; Schellart, Pim; Steeghs, Danny; Szyszka,
Cezary; Unruh, Yvonne; Walton, Nicholas A.; Weston, Simon; Witham,
Andrew; Woudt, Patrick; Zijlstra, Albert
2009MNRAS.399..323G Altcode: 2009arXiv0906.3498G; 2009MNRAS.tmp.1184G
The UV-Excess survey of the northern Galactic plane images a
10° × 185° wide band, centred on the Galactic equator using
the 2.5-m Isaac Newton Telescope in four bands (I5875) down to
~21-22 mag ( in I5875). The setup and data reduction procedures are
described. Simulations of the colours of main-sequence stars, giant,
supergiants, DA and DB white dwarfs and AM Canum Venaticorum stars are
made, including the effects of reddening. A first look at the data of
the survey (currently 30 per cent complete) is given.
---------------------------------------------------------
Title: Solar Surface Magnetism and Irradiance on Time Scales from
Days to the 11-Year Cycle
Authors: Domingo, V.; Ermolli, I.; Fox, P.; Fröhlich, C.; Haberreiter,
M.; Krivova, N.; Kopp, G.; Schmutz, W.; Solanki, S. K.; Spruit, H. C.;
Unruh, Y.; Vögler, A.
2009SSRv..145..337D Altcode:
The uninterrupted measurement of the total solar irradiance during the
last three solar cycles and an increasing amount of solar spectral
irradiance measurements as well as solar imaging observations
(magnetograms and photometric data) have stimulated the development
of models attributing irradiance variations to solar surface
magnetism. Here we review the current status of solar irradiance
measurements and modelling efforts based on solar photospheric
magnetic fields. Thereby we restrict ourselves to the study of solar
variations from days to the solar cycle. Phenomenological models
of the solar atmosphere in combination with imaging observations of
solar electromagnetic radiation and measurements of the photospheric
magnetic field have reached high enough quality to show that a large
fraction (at least, about 80%) of the solar irradiance variability
can be explained by the radiative effects of the magnetic activity
present in the photosphere. Also, significant progress has been made
with magnetohydrodynamic simulations of convection that allow us to
relate the radiance of the photospheric magnetic structures to the
observations.
---------------------------------------------------------
Title: An IPHAS-based search for accreting very low-mass objects
using VO tools
Authors: Valdivielso, L.; Martín, E. L.; Bouy, H.; Solano, E.; Drew,
J. E.; Greimel, R.; Gutiérrez, R.; Unruh, Y. C.; Vink, J. S.
2009mavo.proc..175V Altcode:
We prove that accreting very low-mass (VLM) stars and brown dwarfs (BDs)
can be identified in IPHAS, an Hα emission survey of the northern Milky
Way. Full exploitation of the IPHAS database and a future extension
of it in the southern hemisphere will be useful in identifying
VLM accreting objects near to and far from well-known star-forming
regions. We have used Virtual Observatory (VO) tools to cross-match
the IPHAS catalogue with the 2MASS catalogue. We defined photometric
criteria to identify Hα emission sources with near-infrared colours
similar to those of known young VLM stars and BDs. 4000 candidates were
identified that met our criteria over an area of 1600 square degrees.
---------------------------------------------------------
Title: New young planetary nebulae in IPHAS
Authors: Viironen, K.; Mampaso, A.; Corradi, R. L. M.; Rodríguez,
M.; Greimel, R.; Sabin, L.; Sale, S. E.; Unruh, Y.; Delgado-Inglada,
G.; Drew, J. E.; Giammanco, C.; Groot, P.; Parker, Q. A.; Sokoloski,
J.; Zijlstra, A.
2009A&A...502..113V Altcode: 2009arXiv0904.1937V
Aims: We search for very small-diameter galactic planetary nebulae
(PNe) representing the earliest phases of PN evolution. The IPHAS
catalogue of Hα-emitting stars provides a useful basis for this study
since all sources present in this catalogue must be of small angular
diameter. <BR />Methods: The PN candidates are selected based on their
location in two colour-colour diagrams: IPHAS (r' - Hα) vs. (r' - i'),
and 2MASS (J - H) vs. (H - K_s). Spectroscopic follow-up was carried
out on a sample of candidates to confirm their nature. <BR />Results:
We present a total of 83 PN candidates. We were able to obtain spectra
or find the classification from the literature for 35 candidates. Five
of these objects are likely to be new PNe, including one large bipolar
PN discovered serendipitously close to an emission-line star. PN
distances deduced from extinction-distance relations based on IPHAS
field-star photometry are presented for the first time. These yield
distance estimates for our objects in the range 2 kpc and 6 kpc. From
the data in hand, we conclude that four of the discovered objects are
probably young PNe.
---------------------------------------------------------
Title: An IPHAS-based search for accreting very low-mass objects
using VO tools
Authors: Valdivielso, L.; Martín, E. L.; Bouy, H.; Solano, E.; Drew,
J. E.; Greimel, R.; Gutiérrez, R.; Unruh, Y. C.; Vink, J. S.
2009A&A...497..973V Altcode: 2008arXiv0810.4042V
Context: The main goal of this paper is to prove that accreting very
low-mass stars and brown dwarfs can be identified in IPHAS, an Hα
emission survey of the northern Milky Way. Full exploitation of the
IPHAS database and a future extension of it in the southern hemisphere
will be useful in identifying very low-mass accreting objects near
to and far from well-known star-forming regions. <BR />Aims: We have
used Virtual Observatory tools to cross-match the IPHAS catalogue
with the 2MASS catalogue. We defined photometric criteria to identify
Hα emission sources with near-infrared colours similar to those of
known young very low-mass stars and brown dwarfs. 4000 candidates were
identified that met our criteria over an area of 1600 square degrees. We
present low-resolution optical spectra of 113 candidates. Spectral types
have been derived for the 33 candidates that have spectroscopically
confirmed Hα emission, negligible reddening and spectral class M. We
have also measured Hα emission and investigated the NaI doublet (818.3
nm, 819.5 nm) in these 33 objects. <BR />Methods: We confirm that 33
IPHAS candidates have strong Hα emission indicative of disc accretion
for their spectral type. Twenty-three of them have spectral class M4 or
later, of which ten have classes in the range M5.5-M7.0 and could thus
be very young brown dwarfs. Many objects also have a weak NaI doublet,
an indication of low surface gravity. <BR />Results: IPHAS provides a
very valuable database for identifying accreting very low-mass stars
and brown dwarfs. Virtual Observatory tools provide an efficient method
for identifying these objects over large areas of the sky. Based on our
success rate of 23 Hα emission objects with spectral type in the range
M4-M7 out of 113 candidates with spectroscopic follow-up, we estimate
that there could be hundreds of such objects in the full IPHAS survey.
---------------------------------------------------------
Title: Iphas A-Type Stars with Mid-Infrared Excesses in Spitzer
Surveys
Authors: Hales, Antonio S.; Barlow, Michael J.; Drew, Janet E.; Unruh,
Yvonne C.; Greimel, Robert; Irwin, Michael J.; González-Solares,
Eduardo
2009ApJ...695...75H Altcode: 2009arXiv0901.0909H
We have identified 17 A-type stars in the Galactic Plane that have
mid-infrared (mid-IR) excesses at 8 μm. From observed colors in the
(r' - Hα) - (r' - i') plane, we first identified 23,050 early A-type
main-sequence (MS) star candidates in the Isaac Newton Photometric
H-Alpha Survey (IPHAS) point source database that are located in
Spitzer Galactic Legacy Mid-Plane Survey Extraordinaire Galactic plane
fields. Imposing the requirement that they be detected in all seven
Two Micron All Sky Survey and Infrared Astronomical Satellite bands
led to a sample of 2692 candidate A-type stars with fully sampled 0.6
to 8 μm spectral energy distributions (SEDs). Optical classification
spectra of 18 of the IPHAS candidate A-type MS stars showed that all
but one could be well fitted using MS A-type templates, with the other
being an A-type supergiant. Out of the 2692 A-type candidates 17 (0.6%)
were found to have 8 μm excesses above the expected photospheric
values. Taking into account non-A-Type contamination estimates, the 8
μm excess fraction is adjusted to ~0.7%. The distances to these sources
range from 0.7 to 2.5 kpc. Only 10 out of the 17 excess stars had been
covered by Spitzer MIPSGAL survey fields, of which five had detectable
excesses at 24 μm. For sources with excesses detected in at least two
mid-IR wavelength bands, blackbody fits to the excess SEDs yielded
temperatures ranging from 270 to 650 K, and bolometric luminosity
ratios L <SUB>IR</SUB>/L <SUB>sstarf</SUB> from 2.2 × 10<SUP>-3</SUP>
- 1.9 × 10<SUP>-2</SUP>, with a mean value of 7.9 × 10<SUP>-3</SUP>
(these bolometric luminosities are lower limits as cold dust is not
detectable by this survey). Both the presence of mid-IR excesses and
the derived bolometric luminosity ratios are consistent with many of
these systems being in the planet-building transition phase between
the early protoplanetary disk phase and the later debris disk phase.
---------------------------------------------------------
Title: High spatial resolution empirical 3D extinction mapping
with IPHAS
Authors: Sale, S. E.; Drew, J. E.; Greimel, R.; Unruh, Y. C.; IPHAS
Consortium
2009IAUS..254P..67S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Towards Long-Term Solar Irradiance Modelling: Network Contrasts
from Magneto-Convection Simulations
Authors: Unruh, Y. C.; Solanki, S. K.; Schüssler, M.; Vögler, A.;
Garcia-Alvarez, D.
2009AIPC.1094..768U Altcode: 2009csss...15..768U
Solar irradiance changes on a wide range of time scales and is a key
driver of the Earth's climate where secular variability in particular is
relevant. This is, however, not well understood and our knowledge relies
on reconstructions based on sunspot numbers and similar proxies. <P
/>The prime candidate to produce secular variability is a change
in the surface coverage of small-scale magnetic elements. Direct
observational determination of the flux emitted by these magnetic
elements is difficult, especially as information covering a large
spectral range is needed. Here we present a theoretical approach
to this problem using intensity calculations from 3-D simulations
of solar magneto-convection and compare these with the intensity
calculations used in the successful semi-empirical S ATIRE models at
disk centre. Eventually, such a comparison should lead to the removal
of the last free parameter from S ATIRE-based irradiance reconstruction.
---------------------------------------------------------
Title: High spatial resolution Galactic 3D extinction mapping
with IPHAS
Authors: Sale, Stuart E.; Drew, J. E.; Unruh, Y. C.; Irwin, M. J.;
Knigge, C.; Phillipps, S.; Zijlstra, A. A.; Gänsicke, B. T.; Greimel,
R.; Groot, P. J.; Mampaso, A.; Morris, R. A. H.; Napiwotzki, R.;
Steeghs, D.; Walton, N. A.
2009MNRAS.392..497S Altcode: 2008arXiv0810.2547S
We present an algorithm (MEAD, for `Mapping Extinction Against
Distance') which will determine intrinsic (r' - i') colour, extinction,
and distance for early-A to K4 stars extracted from the IPHAS r'/i'/Hα
photometric data base. These data can be binned up to map extinction in
three dimensions across the northern Galactic plane. The large size of
the IPHAS data base (~200 million unique objects), the accuracy of the
digital photometry it contains and its faint limiting magnitude (r'
~ 20) allow extinction to be mapped with fine angular (~10 arcmin)
and distance (~ 0.1 kpc) resolution to distances of up to 10 kpc,
outside the solar circle. High reddening within the solar circle on
occasion brings this range down to ~2 kpc. The resolution achieved,
both in angle and depth, greatly exceeds that of previous empirical
3D extinction maps, enabling the structure of the Galactic Plane to be
studied in increased detail. MEAD accounts for the effect of the survey
magnitude limits, photometric errors, unresolved interstellar medium
(ISM) substructure and binarity. The impact of metallicity variations,
within the range typical of the Galactic disc is small. The accuracy and
reliability of MEAD are tested through the use of simulated photometry
created with Monte Carlo sampling techniques. The success of this
algorithm is demonstrated on a selection of fields and the results
are compared to the literature.
---------------------------------------------------------
Title: Extremely red stellar objects revealed by IPHAS
Authors: Wright, N. J.; Greimel, R.; Barlow, M. J.; Drew, J. E.; Cioni,
M. -R. L.; Zijlstra, A. A.; Corradi, R. L. M.; González-Solares,
E. A.; Groot, P.; Irwin, J.; Irwin, M. J.; Mampaso, A.; Morris,
R. A. H.; Steeghs, D.; Unruh, Y. C.; Walton, N.
2008MNRAS.390..929W Altcode: 2008MNRAS.tmp.1113W; 2008arXiv0808.2441W
We present photometric analysis and follow-up spectroscopy for
a population of extremely red stellar objects extracted from the
point-source catalogue of the Isaac Newton Telescope (INT) Photometric
Hα Survey (IPHAS) of the northern Galactic plane. The vast majority
of these objects have no previous identification. Analysis of optical,
near- and mid-infrared photometry reveals that they are mostly highly
reddened asymptotic giant branch stars, with significant levels of
circumstellar material. We show that the distribution of these objects
traces galactic extinction, their highly reddened colours being a
product of both interstellar and circumstellar reddening. This is
the first time that such a large sample of evolved low-mass stars
has been detected in the visual and allows optical counterparts to be
associated with sources from recent infrared surveys. <P />Follow-up
spectroscopy on some of the most interesting objects in the sample has
found significant numbers of S-type stars which can be clearly separated
from oxygen-rich objects in the IPHAS colour-colour diagram. We show
that this is due to the positions of different molecular bands relative
to the narrow-band Hα filter used for IPHAS observations. The IPHAS
(r' - Hα) colour offers a valuable diagnostic for identifying S-type
stars. A selection method for identifying S-type stars in the Galactic
plane is briefly discussed and we estimate that over a thousand new
objects of this type may be discovered, potentially doubling the number
of known objects in this short but important evolutionary phase.
---------------------------------------------------------
Title: IPHAS identification of IGR J19267+1325 as a Cataclysmic
Variable
Authors: Steeghs, D.; Knigge, C.; Drew, J.; Unruh, Y.; Greimel, R.
2008ATel.1653....1S Altcode:
We report on optical observations of the galactic plane containing
the X-ray source IGR J19267+1325=1RXS J192626.8+132153 (ATEL
#1649,#1323) using data from the INT Photometric H-Alpha Survey (IPHAS;
http://www.iphas.org ). The field containing the X-ray source was
observed in good observing conditions on August 22 2004 using the Isaac
Newton Telescope at La Palma Observatory and its Wide Field Camera.
---------------------------------------------------------
Title: Initial data release from the INT Photometric Hα Survey of
the Northern Galactic Plane (IPHAS)
Authors: González-Solares, E. A.; Walton, N. A.; Greimel, R.; Drew,
J. E.; Irwin, M. J.; Sale, S. E.; Andrews, K.; Aungwerojwit, A.;
Barlow, M. J.; van den Besselaar, E.; Corradi, R. L. M.; Gänsicke,
B. T.; Groot, P. J.; Hales, A. S.; Hopewell, E. C.; Hu, Haili; Irwin,
J.; Knigge, C.; Lagadec, E.; Leisy, P.; Lewis, J. R.; Mampaso, A.;
Matsuura, M.; Moont, B.; Morales-Rueda, L.; Morris, R. A. H.; Naylor,
T.; Parker, Q. A.; Prema, P.; Pyrzas, S.; Rixon, G. T.; Rodríguez-Gil,
P.; Roelofs, G.; Sabin, L.; Skillen, I.; Suso, J.; Tata, R.; Viironen,
K.; Vink, J. S.; Witham, A.; Wright, N. J.; Zijlstra, A. A.; Zurita,
A.; Drake, J.; Fabregat, J.; Lennon, D. J.; Lucas, P. W.; Martín,
E. L.; Phillipps, S.; Steeghs, D.; Unruh, Y. C.
2008MNRAS.388...89G Altcode: 2008MNRAS.tmp..707G; 2007arXiv0712.0384G
The INT/WFC Photometric Hα Survey of the Northern Galactic Plane
(IPHAS) is an imaging survey being carried out in Hα, r' and i'
filters, with the Wide Field Camera (WFC) on the 2.5-m Isaac Newton
Telescope (INT) to a depth of r' = 20 (10σ). The survey is aimed
at revealing the large scale organization of the Milky Way and
can be applied to identifying a range of stellar populations within
it. Mapping emission line objects enables a particular focus on objects
in the young and old stages of stellar evolution ranging from early
T-Tauri stars to late planetary nebulae. In this paper we present
the IPHAS Initial Data Release, primarily a photometric catalogue
of about 200 million unique objects, coupled with associated image
data covering about 1600 deg<SUP>2</SUP> in three passbands. We note
how access to the primary data products has been implemented through
use of standard virtual observatory publishing interfaces. Simple
traditional web access is provided to the main IPHAS photometric
catalogue, in addition to a number of common catalogues (such as
2MASS) which are of immediate relevance. Access through the AstroGrid
VO Desktop opens up the full range of analysis options, and allows
full integration with the wider range of data and services available
through the Virtual Observatory. The IDR represents the largest data
set published primarily through VO interfaces to date, and so stands
as an exemplar of the future of survey data mining. Examples of data
access are given, including a cross-matching of IPHAS photometry with
sources in the UKIDSS Galactic Plane Survey that validates the existing
calibration of the best data.
---------------------------------------------------------
Title: Spectral irradiance variations: comparison between observations
and the SATIRE model on solar rotation time scales
Authors: Unruh, Y. C.; Krivova, N. A.; Solanki, S. K.; Harder, J. W.;
Kopp, G.
2008A&A...486..311U Altcode: 2008arXiv0802.4178U
Aims: We test the reliability of the observed and calculated spectral
irradiance variations between 200 and 1600 nm over a time span of
three solar rotations in 2004. <BR />Methods: We compare our model
calculations to spectral irradiance observations taken with SORCE/SIM,
SoHO/VIRGO, and UARS/SUSIM. The calculations assume LTE and are based
on the SATIRE (Spectral And Total Irradiance REconstruction) model. We
analyse the variability as a function of wavelength and present time
series in a number of selected wavelength regions covering the UV to
the NIR. We also show the facular and spot contributions to the total
calculated variability. <BR />Results: In most wavelength regions,
the variability agrees well between all sets of observations and the
model calculations. The model does particularly well between 400 and
1300 nm, but fails below 220 nm, as well as for some of the strong NUV
lines. Our calculations clearly show the shift from faculae-dominated
variability in the NUV to spot-dominated variability above approximately
400 nm. We also discuss some of the remaining problems, such as the low
sensitivity of SUSIM and SORCE for wavelengths between approximately
310 and 350 nm, where currently the model calculations still provide
the best estimates of solar variability.
---------------------------------------------------------
Title: Magnetospheric accretion on the T Tauri star BP Tauri
Authors: Donati, J. -F.; Jardine, M. M.; Gregory, S. G.; Petit, P.;
Paletou, F.; Bouvier, J.; Dougados, C.; Ménard, F.; Collier Cameron,
A.; Harries, T. J.; Hussain, G. A. J.; Unruh, Y.; Morin, J.; Marsden,
S. C.; Manset, N.; Aurière, M.; Catala, C.; Alecian, E.
2008MNRAS.386.1234D Altcode: 2008MNRAS.tmp..461D; 2008arXiv0802.2052D
From observations collected with the ESPaDOnS and NARVAL
spectropolarimeters, we report the detection of Zeeman signatures
on the classical T Tauri star (cTTS) BP Tau. Circular polarization
signatures in photospheric lines and in narrow emission lines
tracing magnetospheric accretion are monitored throughout most of
the rotation cycle of BP Tau at two different epochs in 2006. We
observe that rotational modulation dominates the temporal variations
of both unpolarized and circularly polarized spectral proxies tracing
the photosphere and the footpoints of accretion funnels. <P />From
the complete data sets at each epoch, we reconstruct the large-scale
magnetic topology and the location of accretion spots at the surface
of BP Tau using tomographic imaging. We find that the field of BP Tau
involves a 1.2 kG dipole and 1.6 kG octupole, both slightly tilted with
respect to the rotation axis. Accretion spots coincide with the two main
magnetic poles at high latitudes and overlap with dark photospheric
spots; they cover about 2 per cent of the stellar surface. The strong
mainly axisymmetric poloidal field of BP Tau is very reminiscent
of magnetic topologies of fully convective dwarfs. It suggests that
magnetic fields of fully convective cTTSs such as BP Tau are likely not
fossil remants, but rather result from vigorous dynamo action operating
within the bulk of their convective zones. <P />Preliminary modelling
suggests that the magnetosphere of BP Tau extends to distances of at
least 4R<SUB>*</SUB> to ensure that accretion spots are located at high
latitudes, and is not blown open close to the surface by a putative
stellar wind. It apparently succeeds in coupling to the accretion
disc as far out as the corotation radius, and could possibly explain
the slow rotation of BP Tau. <P />Based on observations obtained
at the Canada-France-Hawaii Telescope (CFHT) and at the Télescope
Bernard Lyot (TBL). CFHT is operated by the National Research Council
of Canada, the Institut National des Sciences de l'Univers of the
Centre National de la Recherche Scientifique of France (INSU/CNRS)
and the University of Hawaii, while TBL is operated by CNRS/INSU. <P
/>E-mail: donati@ast.obs-mip.fr (J-FD); mmj@st-andrews.ac.uk
(MMJ); sg64@st-andrews.ac.uk (SGG); petit@ast.obs-mip.fr (PP);
fpaletou@ast.obs-mip.fr (FP); jerome.bouvier@obs.ujf-grenoble.fr
(JB); catherine.dougados@obs.ujf-grenoble.fr (CD);
francois.menard@obs.ujf-grenoble.fr (FM); acc4@st-andrews.ac.uk
(ACC); th@astro.ex.ac.uk (TJH); ghussain@eso.org (GAJH);
y.unruh@imperial.ac.uk (YU); jmorin@ast.obs-mip.fr (JM); scm@aao.gov.au
(SCM); manset@cfht.hawaii.edu (NM); auriere@ast.obs-mip.fr (MA);
claude.catala@obspm.fr (CC); evelyne.alecian@obspm.fr (EA)
---------------------------------------------------------
Title: Doppler images and chromospheric variability of TWA 6
Authors: Skelly, M. B.; Unruh, Y. C.; Collier Cameron, A.; Barnes,
J. R.; Donati, J. -F.; Lawson, W. A.; Carter, B. D.
2008MNRAS.385..708S Altcode: 2008MNRAS.tmp..221S; 2008arXiv0801.0541S
We present Doppler imaging and Balmer line analysis of the weak-line
T Tauri star TWA 6. Using these data we have made one of the first
attempts to measure differential rotation in a T Tauri star, and the
first detection of a slingshot prominence in such a star. We also
show the most direct evidence to date of the existence of solar-type
plages in a star other than the Sun. <P />Observations were made
over six nights: 2006 February 11-13 and 2006 February 18-20, when
spectra were taken with the UCL Echelle Spectrograph on the 3.9-m
Anglo-Australian Telescope. Using least-squares deconvolution to
improve the effective signal-to-noise ratio we produced two Doppler
maps. These show similar features to maps of other rapidly rotating T
Tauri stars, i.e. a polar spot with more spots extending out of it down
to equator. Comparison of the two maps was carried out to measure the
differential rotation. Cross-correlation and parameter fitting indicates
that TWA 6 does not have detectable differential rotation. <P />The
Balmer emission of the star was studied. The mean Hα profile has a
narrow component consistent with rotational broadening and a broad
component extending out to +/-250kms<SUP>-1</SUP>. The variability
in Hα suggests that the chromosphere has active regions that are
cospatial with the spots in the photosphere, similar to the `plages'
observed on the Sun. In addition the star has at least one slingshot
prominence 3R<SUB>*</SUB> above the surface - the first such detection
in a T Tauri star.
---------------------------------------------------------
Title: Five WC9 stars discovered in the AAO/UKST Hα survey
Authors: Hopewell, E. C.; Barlow, M. J.; Drew, J. E.; Unruh, Y. C.;
Parker, Q. A.; Pierce, M. J.; Crowther, P. A.; Knigge, C.; Phillipps,
S.; Zijlstra, A. A.
2005MNRAS.363..857H Altcode: 2005MNRAS.tmp..842H; 2005astro.ph..8187H
We report the discovery of five massive Wolf-Rayet (WR) stars resulting
from a programme of follow-up spectroscopy of candidate emission-line
stars in the Anglo-Australian Observatory United Kingdom Schmidt
Telescope (AAO/UKST) Southern Galactic Plane Hα survey. The 6195-6775
Åspectra of the stars are presented and discussed. A WC9 class is
assigned to all five stars through comparison of their spectra with
those of known late-type WC stars, bringing the known total number of
Galactic WC9 stars to 44. Whilst three of the five WC9 stars exhibit
near-infrared (NIR) excesses characteristic of hot dust emission (as
seen in the great majority of known WC9 stars), we find that two of
the stars show no discernible evidence of such excesses. This increases
the number of known WC9 stars without NIR excesses to seven. Reddenings
and distances for all five stars are estimated.
---------------------------------------------------------
Title: The INT Photometric Hα Survey of the Northern Galactic Plane
(IPHAS)
Authors: Drew, Janet E.; Greimel, R.; Irwin, M. J.; Aungwerojwit,
A.; Barlow, M. J.; Corradi, R. L. M.; Drake, J. J.; Gänsicke,
B. T.; Groot, P.; Hales, A.; Hopewell, E. C.; Irwin, J.; Knigge, C.;
Leisy, P.; Lennon, D. J.; Mampaso, A.; Masheder, M. R. W.; Matsuura,
M.; Morales-Rueda, L.; Morris, R. A. H.; Parker, Q. A.; Phillipps,
S.; Rodriguez-Gil, P.; Roelofs, G.; Skillen, I.; Sokoloski, J. L.;
Steeghs, D.; Unruh, Y. C.; Viironen, K.; Vink, J. S.; Walton, N. A.;
Witham, A.; Wright, N.; Zijlstra, A. A.; Zurita, A.
2005MNRAS.362..753D Altcode: 2005MNRAS.tmp..738D; 2005astro.ph..6726D
The Isaac Newton Telescope (INT) Photometric Hα Survey of the Northern
Galactic Plane (IPHAS) is a 1800-deg<SUP>2</SUP> CCD survey of the
northern Milky Way spanning the latitude range -5° < b < +
5° and reaching down to r'~= 20 (10σ). Representative observations
and an assessment of point-source data from IPHAS, now underway, are
presented. The data obtained are Wide Field Camera images in the Hα
narrow-band, and Sloan r' and i' broad-band filters. We simulate IPHAS
(r'-Hα,r'-i') point-source colours using a spectrophotometric library
of stellar spectra and available filter transmission profiles: this
defines the expected colour properties of (i) solar metallicity stars,
without Hα emission, and (ii) emission-line stars. Comparisons with
observations of fields in Aquila show that the simulations of normal
star colours reproduce the observations well for all spectral types
earlier than M. A further comparison between colours synthesized
from long-slit flux-calibrated spectra and IPHAS photometry for six
objects in a Taurus field confirms the reliability of the pipeline
calibration. Spectroscopic follow-up of a field in Cepheus shows that
sources lying above the main stellar locus in the (r'- Hα,r'-i') plane
are confirmed to be emission-line objects with very few failures. In
this same field, examples of Hα deficit objects (a white dwarf and
a carbon star) are shown to be readily distinguished by their IPHAS
colours. The role IPHAS can play in studies of spatially resolved
northern Galactic nebulae is discussed briefly and illustrated by a
continuum-subtracted mosaic image of Shajn 147 (a supernova remnant,
3° in diameter). The final catalogue of IPHAS point sources will
contain photometry on about 80 million objects. Used on its own, or
in combination with near-infrared photometric catalogues, IPHAS is a
major resource for the study of stellar populations making up the disc
of the Milky Way. The eventual yield of new northern emission-line
objects from IPHAS is likely to be an order of magnitude increase on
the number already known.
---------------------------------------------------------
Title: Probing the circumstellar structures of T Tauri stars and
their relationship to those of Herbig stars
Authors: Vink, Jorick S.; Drew, Janet E.; Harries, Tim J.; Oudmaijer,
René D.; Unruh, Yvonne
2005MNRAS.359.1049V Altcode: 2005MNRAS.tmp..371V; 2005astro.ph..2535V
We present Hα spectropolarimetry observations of a sample of 10 bright
T Tauri stars, supplemented with new Herbig Ae/Be star data. A change in
the linear polarization across Hα is detected in most of the T Tauri
(9/10) and Herbig Ae (9/11) objects, which we interpret in terms of
a compact source of line photons that is scattered off a rotating
accretion disc. We find consistency between the position angle (PA)
of the polarization and those of imaged disc PAs from infrared and
millimetre imaging and interferometry studies, probing much larger
scales. For the Herbig Ae stars AB Aur, MWC 480 and CQ Tau, we find
the polarization PA to be perpendicular to the imaged disc, which is
expected for single scattering. On the other hand, the polarization
PA aligns with the outer disc PA for the T Tauri stars DR Tau and SU
Aur and FU Ori, conforming to the case of multiple scattering. This
difference can be explained if the inner discs of Herbig Ae stars
are optically thin, whilst those around our T Tauri stars and FU
Ori are optically thick. Furthermore, we develop a novel technique
that combines known inclination angles and our recent Monte Carlo
models to constrain the inner rim sizes of SU Aur, GW Ori, AB Aur
and CQ Tau. Finally, we consider the connection of the inner disc
structure with the orientation of the magnetic field in the foreground
interstellar medium: for FU Ori and DR Tau, we infer an alignment of
the stellar axis and the larger magnetic field direction.
---------------------------------------------------------
Title: IPHAS: Surveying the North Galactic Plane in Hα
Authors: Drew, J. E.; Lennon, D. J., Greimel, R.; Zijlstra, A.;
Irwin, J.; Aungwerowijt, A.; Barlow, M. J.; Corradi, R.; Evans,
C. J.; Gaensicke, B.; Groot, P.; Hales, A.; Hopewell, E.; Irwin,
M. J.; Jaigirdar, M.; Knigge, C.; Leisy, P.; Mampaso, A.; Matsuura,
M.; Morales Rueda, L.; Morris, R.; Parker, Q. A.; Phillipps, S.;
Rodríguez Gil, P.; Roelofs, G.; Skillen, I.; Steeghs, D.; Unruh,
Y. C.; Viironen, K.; Vink, J.; Walton, N. A.; Witham, A.; Wright,
N.; Zurita, A.
2005INGN....9....3D Altcode:
H-alpha emission is ubiquitous in our Galaxy. It traces ionised gas of
assorted nebulae such as HII regions, planetary nebulae, Wolf-Rayet
nebulae, and supernova remnants. It is a strong signature of active
stars, interacting binaries, very massive stars (especially supergiants,
Luminous Blue Variables and Wolf-Rayet stars), Be stars, post-AGB stars,
pre-main-sequence stars and so on. These objects represent important
evolutionary phases which are generally short lived, and are hence
few in number and difficult to find. Their discovery is therefore well
worth the effort of a concerted programme and in August 2003 a major
new survey project was started using the Wide Field Camera (WFC)
on the Isaac Newton Telescope (INT) to do just that. It is called
the INT Photometric H-alpha Survey of the Northern Galactic Plane,
or IPHAS for short.
---------------------------------------------------------
Title: IPHAS: The INT/WFC Photometric H-alpha Survey of the Northern
Galactic Plane
Authors: Walton, N. A.; Drew, J.; Barlow, M. J.; Corradi, R.; Drake,
J.; Gaensicke, B.; Greimel, R.; Groot, P.; Irwin, M. J.; Knigge,
C.; Leisy, P.; Lennon, D. J.; Mampaso, A.; Masheder, M.; Morris,
R.; Parker, Q. A.; Phillipps, S.; Pretorius, M.; Rodriguez-Gil,
P.; Skillen, I.; Sokoloski, J.; Steegs, D.; Unruh, Y.; Witham, A.;
Zijlstra, A.; Zurita, A.; IPHAS Collaboration
2004AAS...20511303W Altcode: 2004BAAS...36.1541W
H-alpha emission both traces diffuse ionised nebulae and is commonly
prominent in the spectra of pre- and post-main-sequence stars and
interacting binaries. Since these are mostly relatively short-lived
phases of evolution, they represent a minority of objects in a mature
galaxy like our own at any one time. In the case of interacting
binaries, they are simply hard to find. This scarcity, in turn, has
acted as a brake on our understanding of these crucial evolutionary
stages that, in youth, help shape the growth of planetary systems,
and in old age, determine stellar end states along with the recycling
of energy and chemically enriched matter back into the galactic
environment. <P />IPHAS is our H-alpha survey of the Northern Galactic
Plane being carried out with the 2.5-m Isaac Newton telescope's Wide
Field Camera. Some ∼1800 deg<SUP>2</SUP> of the northern Galactic
plane, over latitudes 5 < b < 5, is being imaged in H-alpha,
r', i' to a depth of r' ∼20 mag. <P />Here we report on the first
120 nights of observations. We comment on the advanced reduction
pipeline employed to generate object catalogues. Early results are
noted, including the discovery of a number of new, hitherto rare,
quadropolar planetary nebulae. The IPHAS objects have been mined to
select candidate samples for followup spectroscopic studies. Extreme
emission line objects are selected from the (r' - H-alpha) v (r' - i')
colour-colour plot. First detections of low mass young stars in the
massive OB association Cyg OB2 are presented. <P />We note how this data
set will be a valuable resource for the emerging Virtual Observatory,
and will be especially powerful when compared with matching multi-colour
IR and optical surveys (e.g. 2MASS and SDSS).
---------------------------------------------------------
Title: Discovery of a WO star in the Scutum-Crux arm of the inner
Galaxy
Authors: Drew, Janet E.; Barlow, M. J.; Unruh, Y. C.; Parker, Q. A.;
Wesson, R.; Pierce, M. J.; Masheder, M. R. W.; Phillipps, S.
2004MNRAS.351..206D Altcode: 2004astro.ph..3482D
We report the discovery of only the fourth massive WO star to be found
in the Milky Way, and only the seventh identified within the Local
Group. This has resulted from the first observations made in a programme
of follow-up spectroscopy of candidate emission-line stars from the
AAO/UKST Southern Galactic Plane Hα Survey. The optical spectrum of
this star, to become WR 93b in the Catalogue of Galactic Wolf-Rayet
stars, is presented and described. WR 93b is classified as WO3 and is
shown to be highly reddened [E(B-V) = 2.1 +/- 0.1]. A recombination-line
analysis of the emission lines yields the abundance ratios C/He = 0.95
and O/He = 0.13 (by number). Comparisons at near-infrared wavelengths of
reddening-corrected photometry between WR 93b and both of Sand 2 (WO3,
D= 49 kpc) and Sand 5 (WO2, D= 1.75 kpc) yield a consistent distance
to WR 93b of 3.4 kpc. Positioned at Galactic coordinates , the star is
most likely located in the Scutum-Crux arm of the inner Milky Way. We
note that none of the four Galactic WO stars lies significantly beyond
the solar circle (with two well inside). <P />Estimation of the wind
terminal velocity in WR 93b at 5750 km s<SUP>-1</SUP> makes this star
the current wind-speed record holder among all non-degenerate stars.
---------------------------------------------------------
Title: Multisite observations of SU Aurigae
Authors: Unruh, Y. C.; Donati, J. -F.; Oliveira, J. M.; Collier
Cameron, A.; Catala, C.; Henrichs, H. F.; Johns-Krull, C. M.; Foing,
B.; Hao, J.; Cao, H.; Landstreet, J. D.; Stempels, H. C.; de Jong,
J. A.; Telting, J.; Walton, N.; Ehrenfreund, P.; Hatzes, A. P.;
Neff, J. E.; Böhm, T.; Simon, T.; Kaper, L.; Strassmeier, K. G.;
Granzer, Th.
2004MNRAS.348.1301U Altcode: 2004astro.ph..1081U
We present results from the 1996 Multi-Site Continuous Spectroscopy
(MUSICOS) campaign on the T Tauri star SU Aurigae. We find a 2.7-d
periodicity in the HeI (587.6 nm) line, and somewhat longer, less
well-pronounced periodicities in the Balmer lines and in Na D. Our
observations support the suggestion that the wind and infall signatures
are out of phase on SU Aur. We present Doppler images of SU Aur that
have been obtained from least-squares deconvolved profiles. Images taken
about one rotation apart show only limited overlap, in particular at low
latitudes. This is due in part to limitations in signal-to-noise ratio,
and in part to line-profile deformations that arise from short-lived
and/or non-surface features. The agreement at high latitudes is better
and suggests that at least some longer-lived features are present. The
analysis of Stokes V profiles yields a marginal magnetic field detection
during one of the phases.
---------------------------------------------------------
Title: Spot sizes on Sun-like stars
Authors: Solanki, S. K.; Unruh, Y. C.
2004MNRAS.348..307S Altcode: 2003astro.ph.11310S
The total area coverage by starspots is of interest for a variety
of reasons, but direct techniques only provide estimates of this
important quantity. Sunspot areas exhibit a lognormal size distribution
irrespective of the phase of the activity cycle, implying that most
sunspots are small. Here we explore the consequences if starspot areas
were similarly distributed. The solar data allow for an increase in
the fraction of larger sunspots with increasing activity. Taking
this difference between the size distribution at sunspot maximum
and minimum, we extrapolate to higher activity levels, assuming
different dependences of the parameters of the lognormal distribution
on total spot coverage. We find that, even for very heavily spotted
(hypothetical) stars, a large fraction of the spots are smaller than
the current resolution limit of Doppler images and hence might be
missed on traditional Doppler maps.
---------------------------------------------------------
Title: Specific Causes of Solar Cycle Irradiance Variability
Authors: Unruh, Y. C.
2004cosp...35.4362U Altcode: 2004cosp.meet.4362U
The total solar irradiance has varied by about 0.1% between solar
cycle minimum and maximum during the last couple of cycles. These
variations are highly wavelength dependent with changes of an order of
magnitude larger in the UV than in the visible. I discuss some of the
proposed causes of total and spectral solar irradiance variability,
and in particular the contribution of magnetic surface features.
---------------------------------------------------------
Title: Resolved polarization changes across Hα in the classical
T Tauri star RY Tauri
Authors: Vink, Jorick S.; Drew, J. E.; Harries, T. J.; Oudmaijer,
R. D.; Unruh, Y. C.
2003A&A...406..703V Altcode: 2003astro.ph..6095V
We present linear Hα spectropolarimetry of the classical T Tauri
star RY Tau. A change in the polarization percentage and position
angle across Hα is detected, which suggests that line photons are
scattered in a rotating disc. We derive the position angle from the
slope of the loop in the (Q,U) diagram and find it to be 146 +/- 3
degree. This is perpendicular to the position angle of the disc of 48
+/- 5 degree as deduced from millimeter imaging by Koerner & Sargent
(\cite{Koerner1995}). This finding is consistent, as scattering off the
imaged millimeter disc is expected to yield a polarization signature in
a direction that is rotated by 90 degree from this disc. The observed
spectropolarimetric behaviour of RY Tau is reminiscent of that seen
in a large group of Herbig Ae stars, suggesting a common circumstellar
origin of the polarized photons.
---------------------------------------------------------
Title: Reconstruction of solar irradiance variations in cycle 23:
Is solar surface magnetism the cause?
Authors: Krivova, N. A.; Solanki, S. K.; Fligge, M.; Unruh, Y. C.
2003A&A...399L...1K Altcode:
A model of solar irradiance variations is presented which is based
on the assumption that solar surface magnetism is responsible for all
total irradiance changes on time scales of days to years. A time series
of daily magnetograms and empirical models of the thermal structure
of magnetic features (sunspots, faculae) are combined to reconstruct
total (and spectral) irradiance from 1996 to 2002. Comparisons with
observational data reveal an excellent correspondence, although the
model only contains a single free parameter. This provides strong
support for the hypothesis that solar irradiance variations are caused
by changes in the amount and distribution of magnetic flux at the
solar surface.
---------------------------------------------------------
Title: Solar Variability and Climate Change; Poster Summary
Authors: Unruh, Y.
2002EGSGA..27.6708U Altcode:
I will give a brief overview of the posters presented in session ST20
and link them into the context of the talks presented. This will be
complemented by my necessarily incomplete and personal selection of
some poster highlights.
---------------------------------------------------------
Title: Irradiance Medels based on Magnetic Activity
Authors: Solanki, S.; Krivova, N.; Unruh, Y.
2002cosp...34E1357S Altcode: 2002cosp.meetE1357S
An introduction is given to the modelling of irradiance variations
based on solar surface magnetism. We describe how a time series of daily
magnetograms and empirical models of the thermal structure of magnetic
features (sunspots, magnetic elements) are combined to reconstruct total
and spectral irradiance on a time scale of weeks to years. Comparisons
with observational data reveal an excellent correspondence. On a
longer time scale of decades to centuries we first need to know how
the Sun's magnetic field evolved. Hence reconstructions of the Sun's
total magnetic flux are briefly introduced, before we present longer
term reconstructions of the total and spectral irradiance since the
Maunder minimum.
---------------------------------------------------------
Title: The influence of an inclined rotation axis on solar irradiance
variations
Authors: Knaack, R.; Fligge, M.; Solanki, S. K.; Unruh, Y. C.
2001A&A...376.1080K Altcode:
Compared with Sun-like stars, the irradiance variations of the
Sun over the solar cycle appear to be relatively small for its
average activity level (Lockwood et al. \cite{Lockwood:etal:1992};
Radick et al. \cite{Radick:etal:1998}). It has been proposed that
the special position of Earth-based observers in the ecliptic plane
may give the impression of a subdued solar photometric variability
(Schatten \cite{Schatten:1993}). The aim of the present paper is to
examine the influence on irradiance variations of a solar rotation
axis inclined towards the observer. A three-component model is
used to calculate relative flux variations of a given active-region
distribution on the surface of the Sun as a function of inclination
and wavelength. Wavelength-dependent intensity spectra are used to
describe the contributions of the undisturbed photosphere, sunspots and
faculae. The spectra result from models that have successfully been
used to reproduce a host of solar data and thus represent realistic
estimates of the radiative output from these solar features. We find
that an inclined rotation axis increases the total solar irradiance
variations maximally by 40%. The most probable value is approximately
6%. This is much less than that suggested by former studies, which
were based on simple contrast functions. In the averaged Strömgren
filters we estimate a most probable increase of the solar variability
of 30%. In addition, we estimate the dependence of the flux in the
chromospheric Ca II H&K lines on inclination. We find that the
average chromospheric activity level depends only slightly on the
inclination angle. The chromospheric variability of Sun-like stars,
however, is significantly affected. Nonetheless, our results indicate
that a different average inclination of stellar rotation axes relative
to the observer cannot explain the discrepancy between the brightness
variations of the Sun and Sun-like stars.
---------------------------------------------------------
Title: Diagnostics from Spectral Irradiance Measurements
Authors: Unruh, Y. C.; Solanki, S. K.
2001AGUSM..SP32B01U Altcode:
Solar irradiance varies in tune with solar activity. The irradiance
changes show a strong wavelength dependence, being an order of magnitude
larger in the UV than in the visible. The spectral dependence of the
irradiance variations can be used to differentiate between mechanisms
that may be responsible for the irradiance changes. I review some of
the mechanisms that have been invoked in the past to explain the solar
irradiance variations and compare their predicted spectral irradiance
changes with solar irradiance measurements. The comparisons imply
that surface magnetic features alone are sufficient to explain solar
irradiance data.
---------------------------------------------------------
Title: Stellar Irradiance Variations Caused by Magnetic Activity:
The Influence of an Inclined Rotation Axis
Authors: Knaack, R.; Fligge, M.; Solanki, S. K.; Unruh, Y. C.
2001ASPC..248..227K Altcode: 2001mfah.conf..227K
No abstract at ADS
---------------------------------------------------------
Title: Are the Sun's Brightness Variations Really Tamer than Those of
Other Comparable Solar-type Stars? (CD-ROM Directory: contribs/unruh1)
Authors: Unruh, Y. C.; Knaack, R.; Fligge, M.; Solanki, S. K.
2001ASPC..223..748U Altcode: 2001csss...11..748U
No abstract at ADS
---------------------------------------------------------
Title: Doppler Images of LW Hydrae (CD-ROM Directory: contribs/unruh2)
Authors: Unruh, Y. C.; Gatti, A. A.; Drew, J. E.; Roberts, G.; van Wyk,
F.; Marang, F.; Kilkenny, D.
2001ASPC..223.1320U Altcode: 2001csss...11.1320U
No abstract at ADS
---------------------------------------------------------
Title: Variations of the Solar Spectral Irradiance
Authors: Solanki, S. K.; Fligge, M.; Unruh, Y. C.
2001IAUS..203...66S Altcode:
Not just the total solar irradiance is known to vary, but also the
solar spectrum. Observations and models of solar spectral irradiance
variations are presented.
---------------------------------------------------------
Title: Preliminary MUSICOS 96 results on Balmer line variability on
the T Tauri star SU aurigae
Authors: Oliveira, J. M.; Unruh, Y. C.; Foing, B. H.; MUSICOS 1996
Collaboration
2001AdSpR..26.1747O Altcode:
The study of young stellar objects is essential for the further
understanding of the early evolutionary stages of the Sun and
similar low-mass stars. In this context, T Tauri stars supply valuable
information on their pre-main sequence evolution. SU Aur is a classical
T Tauri star that shows little veiling and few emission lines. The
Balmer line profiles are extremely variable, even on short time
scales. We present results from the analysis of the variability of
these spectral lines, based on a data set obtained during the world-wide
multi-site spectroscopic MUSICOS 1996 campaign. We attempt to describe
the interaction of the stellar magnetosphere and the accretion disk,
and search for the signatures of mass inflow and ejection.
---------------------------------------------------------
Title: Spectral Line Variability in the Circumstellar Environment
of the Classical T Tauri Star SU Aurigae (CD-ROM Directory:
contribs/oliveira)
Authors: Oliveira, J. M.; Foing, B. H.; Unruh, Y. C.
2001ASPC..223..539O Altcode: 2001csss...11..539O
No abstract at ADS
---------------------------------------------------------
Title: Modelling solar irradiance variations: Comparison with
observations, including line-ratio variations
Authors: Unruh, Y. C.; Solanki, S. K.; Fligge, M.
2000SSRv...94..145U Altcode:
Solar irradiance variations show a strong temporal and spectral
dependence. The progression of the Sun through its activity cycle as
well as solar rotation are mirrored in the irradiance variations. The
spectral dependence is such that the variations are several magnitudes
larger in the EUV than in the visible or infrared. We present a simple
3-component model that is based on the assumption that changes in
the solar flux are exclusively due to changes in spot and facular
coverage. We compare our model to observations of the spectral solar
irradiance variations. Despite its simplicity, we find that the
agreement between our model and the observations is surprisingly
good. We also explore the reliability and the limitations of our
approach by comparing observations of the solar facular contrast and
of the changes in spectral line depths with our calculations.
---------------------------------------------------------
Title: Modelling Short-Term Spectral Irradiance Variations
Authors: Fligge, M.; Solanki, S. K.; Unruh, Y. C.
2000SSRv...94..139F Altcode:
On time-scales of the solar rotation most of the solar irradiance
variations are caused by the changing distribution of solar surface
magnetic features. We model these short-term irradiance variations
using calculations of sunspot and facular contrasts as a function of
wavelength and limb angle on the Sun. The position of active regions on
the solar disc is derived from the MDI magnetograms. The reconstructed
irradiance variations are compared with total and spectral irradiance
measurements obtained by the VIRGO experiment on SOHO.
---------------------------------------------------------
Title: Magnetospheric accretion and winds on the T Tauri star SU
Aurigae. Multi-spectral line variability and cross-correlation
analysis
Authors: Oliveira, J. M.; Foing, B. H.; van Loon, J. Th.; Unruh, Y. C.
2000A&A...362..615O Altcode: 2000astro.ph..9087O
SU Aurigae is a T Tauri star that was well monitored during the MUSICOS
96 multi-site campaign. We present the results of the spectroscopic
analysis of the circumstellar environment of this star, particularly
of the Hα , Hβ , Na I D and He I D3 line profiles. The signatures of
modulated outflows and mass accretion events are analysed, as well as
transient spectral features. We compute the cross-correlation function
(CCF) of several pairs of (velocity bins in) spectral lines to better
investigate the profiles' temporal variability. We found increasing
time lags between the variability of He I D3, Na I D and Hβ . We
propose this may be understood in terms of azimuthal distortion of the
magnetic field lines due to the different rotation rates of the star
and the disk. We find the slightly blueshifted absorption features in
Hα , Hβ \ and Na I D to be anti-correlated with the accretion flow
signatures. We propose that the transient absorption features in the
blue wings of Hα , Hβ \ and Na I D (signatures of mass outflows),
and flare brightenings are related to the disruption of distorted
magnetospheric field lines. Based on observations obtained during the
MUSICOS~96 campaign in which were involved: Isaac Newton Telescope
(INT, La Palma), Observatoire de Haute Provence (OHP, France), McDonald
Observatory (MDO, USA), Beijing Astronomical Observatory (BAO, Xinglong,
China) and Canada-France-Hawaii Telescope (CFHT, Hawaii).
---------------------------------------------------------
Title: Modelling irradiance variations from the surface distribution
of the solar magnetic field
Authors: Fligge, M.; Solanki, S. K.; Unruh, Y. C.
2000A&A...353..380F Altcode:
An important question in solar physics is to what extent solar surface
magnetism affects the solar irradiance. Previous attempts to answer this
question have employed proxies of the magnetic field to reconstruct the
irradiance and compare it with observations. Here we present the first
model calculations of solar irradiance variations based on variations
of the surface distribution of the solar magnetic field. The irradiance
reconstruction makes use of sunspot and facular contrasts calculated
as a function of wavelength and limb angle on the Sun. The position
and size of magnetic features on the solar disk are extracted from
full-disk magnetograms obtained by the Michelson Doppler Interferometer
(MDI) onboard the SOHO spacecraft. The reconstructed spectral irradiance
variations are compared with total and spectral contrast measurements
obtained by the VIRGO instrument onboard SOHO. Our reconstructions are
able to reproduce variations on the time-scale of the solar rotation
with much greater accuracy than previous models based on disk-integrated
magnetic proxies.
---------------------------------------------------------
Title: The influence of an inclined rotation axis on solar irradiance
variations
Authors: Knaack, R.; Fligge, M.; Solanki, S. K.; Unruh, Y. C.
2000ssls.work...45K Altcode:
The irradiance variations of the Sun over the solar cycle are relatively
small compared with sun-like stars (Radick et al., 1998). It has been
proposed that a random distribution of stellar rotation axes relative to
the ecliptic plane could explain their larger variability (Schatten,
1993). We examine the influence on total irradiance variations of
the inclination of the solar rotation axis relative to an observer. A
three-component model is used to calculate the relative flux variations
of a given distribution of active regions on the surface of the Sun as
a function of the inclination. One component is the quiet Sun, another
is a sunspot component and the third describes the faculae. We find
that the inclination effect increases the total irradiance variations
of the Sun maximally by 40%. The most probable value is approximately
5%. This is much less than former studies (Schatten, 1993, Radick et
al., 1998) suggested.
---------------------------------------------------------
Title: Solar Surface Magnetism and the Increase of Solar Irradiance
between Activity Minimum and Maximum
Authors: Fligge, M.; Solanki, Sami K.; Meunier, Nadege; Unruh,
Yvonne C.
2000ESASP.463..117F Altcode: 2000sctc.proc..117F
No abstract at ADS
---------------------------------------------------------
Title: Modelling Solar Irradiance Variations: Comparison with
Observations, Including Line-Ratio Variations
Authors: Unruh, Y. C.; Solanki, S. K.; Fligge, M.
2000svc..book..145U Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Modelling Short-Term Spectral Irradiance Variations
Authors: Fligge, M.; Solanki, S. K.; Unruh, Y. C.
2000svc..book..139F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Spectral Line Variability in the Circumstellar Environment
of the Classic al T Tauri Star SU Aurigae
Authors: Oliveira, J. M.; Foing, B. H.; Unruh, Y. C.
1999astro.ph.12199O Altcode:
SU Aurigae is a classical T Tauri star of spectral type G2. This star
was one of the scientific targets of the MUSICOS 96 multi-site campaign
that provided a wealth of high resolution cross-dispersed spectral data
with a good continuous time coverage. We present the results of the
analysis of the complex circumstellar environment of this star, with
particular regard to magnetospheric models, in which the accretion from
the disk is channelled onto the star along magnetic field lines. The
signatures of modulated outflows and mass accretion events are present
in the spectra, as well as transient spectral features. We computed
auto-correlation and cross-correlation functions to better investigate
the source of the profiles' variability. The comparison of the profiles
of different spectral lines allows us to study the footprints of events
effectively observed at different distances from the stellar surface.
---------------------------------------------------------
Title: Coronal emission and dynamo saturation
Authors: Jardine, M.; Unruh, Y. C.
1999A&A...346..883J Altcode:
We show that the observed saturation of X-ray emission with increasing
rotation rate in solar-type stars does not necessarily imply saturation
of the underlying dynamo. This effect can be caused by the centrifugal
stripping of the corona. As the stellar rotation rate is increased,
centrifugal forces cause a rise in the pressure and density in the outer
parts of the largest magnetic loops. This may explain the observed
formation of large prominences close to the co-rotation radius where
centrifugal forces begin to dominate over gravity. In order for these
massive prominences to be contained against centrifugal ejection, the
coronal magnetic field must be highly stressed and must be evolving
on a timescale of a few days as determined by the observed prominence
lifetime. We postulate that the co-rotation radius marks the position
at which the corona becomes distorted by centrifugal forces. As the
stellar rotation rate is increased, the co-rotation radius moves closer
to the surface, reducing the extent of the “undisturbed” corona. We
take as illustrative examples two simple field topologies and show
that if the X-ray emission comes only from this undisturbed volume,
then a saturation of the X-ray emission with increasing rotation rate
occurs naturally. This effect may mimic true dynamo saturation or
disguise its onset.
---------------------------------------------------------
Title: Short-term spectroscopic variability in the pre-main sequence
Herbig AE star AB Aurigae during the MUSICOS 96 campaign
Authors: Catala, C.; Donati, J. F.; Böhm, T.; Landstreet, J.;
Henrichs, H. F.; Unruh, Y.; Hao, J.; Collier Cameron, A.; Johns-Krull,
C. M.; Kaper, L.; Simon, T.; Foing, B. H.; Cao, H.; Ehrenfreund, P.;
Hatzes, A. P.; Huang, L.; de Jong, J. A.; Kennelly, E. J.; ten Kulve,
E.; Mulliss, C. L.; Neff, J. E.; Oliveira, J. M.; Schrijvers, C.;
Stempels, H. C.; Telting, J. H.; Walton, N.; Yang, D.
1999A&A...345..884C Altcode:
We present results of the spectroscopic monitoring of AB Aur obtained
during the MUSICOS 96 campaign. The analysis is mainly focussed on the
He I D3 line, on the Hα line, and on a set of photospheric lines. The
star was monitored irregularly for more than 200 hours. We confirm
the high level of variability of spectral lines in AB Aur. We find
that the photospheric lines have a profile differing significantly
from a classical rotational profile. The dominant features of this
abnormal photospheric profile are a blue component, in absorption, whose
velocity is modulated with a 34hr period, and a red component, stable
in velocity but of variable intensity, with a possible periodicity
near 43 hrs. The He I D3 line exhibits two well-defined components:
a blue component, always in emission with a velocity modulated with a
45hr period, and a red component of variable intensity, alternatively
in emission and in absorption, occurring at a fixed velocity, with a
variable intensity possibly modulated with a 45 hr period. The Hα line,
showing a P Cygni profile, also exhibits pseudo-periodic variations
of its blue absorption component, but its variability appears more
complicated than that of the other lines studied here. We suggest
that the blue component of the photospheric lines is modulated by the
star's rotation, with a period of 34 hrs, due to a highly inhomogeneous
photosphere, involving significant radial flows. Our model also involves
downflows onto the stellar pole to account for the red components of the
photospheric lines and of the He I D3 line. We propose two different
interpretations of the behavior of the blue component of the He I D3
line. In the first one, this component is formed in a wind originating
from the star's equatorial regions. In this interpretation, the rotation
period of the equatorial regions of the star is 45 hrs, implying a 25%
surface differential rotation, with the pole rotating faster than the
equator. The second interpretation involves a wind originating from
a region of a circumstellar disk, at a distance of 1.6 stellar radii
from the star's center, with a rotation period of 45 hrs. We are not
able to decide which one of these two interpretations is more likely,
on the basis of the data presented here. Based on observations obtained
during the MUSICOS 96 MUlti-SIte COntinuous Spectroscopic campaign,
collected at the Canada-France Hawaii, the McDonald 2.1m, the La
Palma 2.5m Isaak Newton, the Observatoire de Haute-Provence 1.93m,
the Xinglong 2.16m, and the Ritter Observatory 1m telescopes
---------------------------------------------------------
Title: Optical and ultraviolet observations of a strong flare in
the young, single K2 dwarf LQ Hya
Authors: Montes, D.; Saar, S. H.; Collier Cameron, A.; Unruh, Y. C.
1999MNRAS.305...45M Altcode: 1998astro.ph.11452M
We present high-resolution optical echelle spectra and IUE observations
during a strong flare on 1993 December 22 in the very active, young,
rapidly rotating, single K2 dwarf LQ Hya. The initial impulsive
phase of the flare, which started sometime between 2:42 ut and 4:07
ut, was characterized by strong optical continuum enhancement and
blueshifted emission lines with broad wings. The optical chromospheric
lines reached their maximum intensity at ~ 5:31 ut, by which time the
blueshift vanished and the optical continuum enhancement had sharply
decreased. Thereafter, the line emission slowly decreased and the lines
redshift in a gradual phase that lasted at least two more hours. The
Mg II lines behaved similarly. Quiescent C IV flux levels were not
recovered until 21 h later, though a data gap and a possible second
flare make the interpretation uncertain. In addition to the typically
flare-enhanced emission lines (e.g., H alpha and H beta), we observe
He I D_3 going into emission, plus excess emission (after subtraction
of the quiescent spectrum) in other He I and several strong neutral
metal lines (e.g., Mg I b). Flare enhancement of the far-ultraviolet
continuum generally agrees with an Si I recombination model. We
estimate the total flare energy, and discuss the broad components,
asymmetries and Doppler shifts seen in some of the emission lines.
---------------------------------------------------------
Title: The spectral dependence of facular contrast and solar
irradiance variations
Authors: Unruh, Y. C.; Solanki, S. K.; Fligge, M.
1999A&A...345..635U Altcode:
We present model calculations of facular and sunspot contrasts as a
function of wavelength and limb angle on the Sun. These are the first
such calculations; they assume LTE and are based on opacity distribution
functions (ODFs). The calculated facular contrasts as a function of
limb angle fit into the general picture of contrast measurements,
and the behaviour of the contrast with wavelength at a given limb
angle is in excellent agreement with the measurements. The calculated
intensity spectra are used to construct the solar flux spectrum for
different levels of solar activity. It is assumed that the irradiance
or flux variations are due to changes in the sunspot and facular
filling factors. The model atmosphere used to calculate the facular
intensities has been tuned so that the calculated irradiance variations
match the observed total and spectral irradiance variations during
the last solar cycles. The model calculations have also been used
to estimate the relative importance of continuum and spectral-line
variations in producing irradiance variations. The results suggest
that the continuum variations only contribute negligibly to the total
irradiance variations on solar-cycle time scales.
---------------------------------------------------------
Title: Latitude distributions and lifetimes of star-spots on G dwarfs
in the alpha Persei cluster
Authors: Barnes, J. R.; Collier Cameron, A.; Unruh, Y. C.; Donati,
J. F.; Hussain, G. A. J.
1998MNRAS.299..904B Altcode:
We present a set of maximum-entropy reconstructions of the star-spot
distributions on two rapidly rotating G dwarfs in the alpha Persei
cluster, from spectra taken at the William Herschel Telescope on
three nights in 1996 October and November. Since these stars are too
faint for conventional Doppler imaging, which makes use of only one
or a few lines, we take the large number of photospheric metal lines
available in an echelle spectrum, and deconvolve them into a single,
high signal-to-noise ratio profile. We show that this technique results
in a typical multiplex gain of 22.5 in signal-to-noise ratio for a
given spectrum, the equivalent of using a single line obtained on
a 63-m telescope. The image reconstructions demonstrate that both
these stars have cool high-latitude regions or polar crowns, and
low-latitude features, in contradiction to the suggestion that only
high-latitude spots should be present. Cross-correlation between image
reconstructions of He 699, 31 days apart, reveals a lack of correlation
between detailed small-scale structures. This places an upper limit
for the lifetime of the observed features at less than one month. The
Hα profiles are also found to exhibit absorption features indicating
the presence of prominence clouds, at or below the corotation radius.
---------------------------------------------------------
Title: A model of solar total and spectral irradiance variations
Authors: Fligge, M.; Solanki, S. K.; Unruh, Y. C.; Froehlich, C.;
Wehrli, Ch.
1998A&A...335..709F Altcode:
We model solar spectral irradiance variations under the assumption
that they are produced by sunspots and faculae alone. The model is
based on three components, i.e. quiet Sun, assumed to be temporally
invariant, sunspots and faculae whose temporal variations are mimicked
using time series of sunspot areas and Mg II core-to-wing ratios. The
detailed flux spectrum for each component is employed. The results
are compared to spectral irradiance measurements at 402 nm, 500 nm
and 862 nm obtained between February 22 and December 31, 1996 by
the three-channel sunphotometers (SPM) which are part of the VIRGO
package onboard SOHO. Our model shows a good correlation with the
measured variations of the three colour channels and of the total
irradiance. Since it also successfully reproduces changes in the UV
spectral irradiance, irradiance variations and observed variations
of the faculae-to-spots filling factor ratio since 1978, our model
supports earlier suggestions that a large part of the solar irradiance
variations is caused by magnetic fields at the solar surface. Finally,
we use the model to test whether the difference between the magnitude
of solar and stellar brightness variations reported by Lockwood et
al. (1992) is due to the particular filters they use for their stellar
observations. Our results suggest that this effect can explain only
a small part of the discrepancy.
---------------------------------------------------------
Title: Surface inhomogeneities and line variability on DF Tau
Authors: Unruh, Y. C.; Collier Cameron, A.; Guenther, E.
1998MNRAS.295..781U Altcode:
We have mapped surface inhomogeneities on the classical T Tauri star DF
Tau, using the Lii doublet at 670.8 nm, the Cai lines at 612.2 nm and
643.9 nm and a calcium and iron blend at 646.3 nm. We find compelling
evidence that there are hotspots with temperatures of more than 5000
K. Two of the hotspots produce line-profile deformations that can
be traced as they move through the cross-correlated profiles. When
one of the hotspots crosses the stellar disc, redshifted absorption
components appear in the Na D lines. As these redshifted absorption
features are usually tracers for mass-infall we interpret this hotspot
as an accretion shock close to the stellar surface. Parts of the surface
of DF Tau are covered with a hot chromosphere that is visible in the
Caii infrared triplet lines and the narrow component of Hei. We find
no correlation between the veiling and the lines that originate from
the hot chromosphere, suggesting that the veiling and the chromospheric
emission are produced in physically distinct regions.
---------------------------------------------------------
Title: Prominences on Rapidly-Rotating Solar-Type Stars
Authors: Jardine, M.; Barnes, J.; Unruh, Y.; Collier Cameron, A.
1998ASPC..150..235J Altcode: 1998npsp.conf..235J; 1998IAUCo.167..235J
No abstract at ADS
---------------------------------------------------------
Title: MUSICOS Observations of SU AUR
Authors: Unruh, Yvonne C.; Donati, J. -F.; Balona, L.; Bohm, T.;
Cao, H.; Catala, C.; Collier Cameron, A.; Ehrenfreund, P.; Foing,
B.; Granzer, T.; Hao, J.; Hatzes, A.; Henrichs, H.; Johns-Krull,
C.; de Jong, J.; Kennelly, T.; Landstreet, J.; Morrison, N.; Mullis,
C.; Neff, J.; Oliveira, J.; Schrijvers, C.; Simon, T.; Stempels, E.;
Strassmeier, K. G.; Telting, J.; Walton, N.
1998ASPC..154.2064U Altcode: 1998csss...10.2064U
We present first results of the high-resolution observations of SU Aur
obtained through the MUSICOS network in 1996 Nov. The data set is unique
in that it gives us complete phase coverage for almost two rotation
periods of SU Aur. This is particularly valuable for T Tauri stars as
they can vary dramatically on the time scale of one rotation period.
---------------------------------------------------------
Title: A model of the wavelength dependence of solar irradiance
variations
Authors: Solanki, S. K.; Unruh, Y. C.
1998A&A...329..747S Altcode:
The variation of the solar irradiance over the solar cycle has a strong
wavelength dependence, being larger at shorter wavelengths. Here
we present simple models of the spectral dependence of irradiance
variations between solar activity maximum and minimum. We find that the
observations (which concentrate on the UV) cannot be reproduced by a
change in effective temperature of the Sun (or of parts of its surface)
alone. We can, however, reproduce the data with either a 2-component or
a 3-component model, of which one component is the quiet Sun, another
is a facular component, and the third (in the case of the 3-component
model) represents the temperature stratification of sunspots. The
facular component is found to be very close to the facular models F
or P of Fontenla et al. (1993). The success of these models supports
the assumption underlying many studies of total solar irradiance
variations that these are caused mainly by magnetic fields at the solar
surface. Our investigation also allows an improved estimate of the
relative contribution of the various layers in the solar photosphere and
of the different wavelength regions to the total irradiance variations.
---------------------------------------------------------
Title: The Wavelength Dependence of Solar Irradiance Variations
Authors: Unruh, Yvonne C.; Solanki, Sami K.
1998ASPC..154..700U Altcode: 1998csss...10..700U
The observed irradiance variations over a solar cycle show a strong
wavelength dependence; the variations are strongest in the UV and
very weak in the visible. Here we present a simple model of the
spectral dependence of the solar irradiance. We can exclude models that
postulate a change in the effective temperature of the Sun or of parts
of the Sun. However, we find that the observed irradiance variations
can be matched with a model that includes the different temperature
stratification of the quiet photosphere, the faculae and the sunspots.
---------------------------------------------------------
Title: MUSICOS Observations of SU Aurigae
Authors: Unruh, Y. C.; Donati, J. -F.; et al.
1998cvsw.conf..355U Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Strong Flare on the K Dwarf LQ Hya
Authors: Montes, D.; Saar, S. H.; Collier Cameron, A.; Unruh, Y. C.
1998ASPC..154.1508M Altcode: 1998csss...10.1508M
We present high resolution optical echelle spectra and IUE SWP
observations during a strong flare on 1993 December 22 in the very
active, young, rapidly rotating, single K2 dwarf LQ Hya. The temporal
evolution of the flare consists of an initial impulsive phase,
characterized by strong continuum enhancement, which started between
02:42 UT (quiescent spectrum) and 04:36 UT (first spectrum with a strong
increase in the chromospheric lines). The chromospheric lines reached
their maximum intensity ~55 min later, by which time the continuum
enhancement had sharply decreased. Thereafter, the line emission slowly
decreased in a gradual phase that lasted at least until the end of
the observation (07:29 UT). IUE data indicate that quiescent C iv flux
levels were not recovered after ~4 UT on the following day. We describe
the variation of the continuum enhancement, the optical and the UV lines
during the flare. In addition to the emission lines that show strong
flare enhancement (e.g., Hα and Hβ), we observe He i D<SUB>3</SUB>
going into emission. After subtraction of the quiescent spectrum,
we also observe excess emission in He i lines at 4921.9, 5015.7, and
6678.1AA, and in other metal lines such as the Na i D<SUB>1</SUB> and
D<SUB>2</SUB>, the Mg i b triplet and several Fe i and Fe ii lines. We
estimate the energy release during the flare, and analyze the broad
components and asymmetries seen in some of the emission lines.
---------------------------------------------------------
Title: Balmer Line Profiles Variations in SU Aurigae from the MUSICOS
96 Multi-site Campaign
Authors: Oliveira, J. M.; Unruh, Y. C.; Foing, B. H.; MUSICOS 96
Collaboration
1998Ap&SS.261..143O Altcode: 1999Ap&SS.261..143O
No abstract at ADS
---------------------------------------------------------
Title: Modelling Spectral Irradiance Variations obtained by VIRGO
Authors: Fligge, M.; Solanki, S. K.; Unruh, Y.; Frohlich, C.;
Wehrli, Ch.
1998ASPC..140..311F Altcode: 1998ssp..conf..311F
No abstract at ADS
---------------------------------------------------------
Title: Wavelength Dependence of Solar Irradiance Variability from
VIRGO Onboard SOHO
Authors: Wehrli, C.; Fröhlich, C.; Anklin, M.; Fligge, M.; SOlanki,
S. K.; Unruh, Y.
1997ESASP.415..497W Altcode: 1997cpsh.conf..497W
No abstract at ADS
---------------------------------------------------------
Title: Does chromospheric emission mimic polar starspots in Doppler
images?
Authors: Unruh, Y. C.; Collier Cameron, A.
1997MNRAS.290L..37U Altcode:
We have used time-series spectra of the sodium doublet at 589.0 and
589.6nm in AB Doradus to investigate the effects of a chromospheric
temperature rise on Doppler images derived from strong lines whose
cores are formed in the upper photosphere and lower chromosphere. On
solar-type stars, the NaD lines probe a range of heights and tend
to be much more sensitive to the chromospheric temperature structure
than the weaker photospheric lines that are commonly used for Doppler
imaging. Contrary to suggestions that polar spots may be an artefact
arising from chromospheric emission reversals, we find that the images
obtained from the NaD lines show less high-latitude structure, and give
more reliable light-curve predictions, than images derived previously
from fits to several weaker photospheric lines.
---------------------------------------------------------
Title: Doppler imaging of AB Doradus using the Lii 6708 line
Authors: Hussain, G. A. J.; Unruh, Y. C.; Collier Cameron, A.
1997MNRAS.288..343H Altcode:
We present maximum entropy reconstructions of the stellar surface
of the K0 dwarf AB Doradus using observations obtained in 1993
November. Doppler images are produced using the Lii 6708-Angstroms line
and compared to images produced using Cai and Fei lines. An Li abundance
of log N(Li) = 2.9 +/- 0.3 is measured using local thermodynamic
equilibrium (LTE) profile synthesis. By assessing how enhanced spot
Li abundances affect fits between synthetic reconstructions and the
observed data, we conclude that the presence of starspots is unlikely to
lead to an overestimation of the photospheric Li abundance. Moreover,
Li abundances in starspots do not appear to be enhanced with respect
to the photospheric level. The equivalent width measurements for
the Lii 6708-Angstroms line are strengthened by the presence of
starspots. This effect is probably due to their lower effective
temperatures. Because the spots were widely distributed in longitude
at the time of observation, the extent to which the Lii line equivalent
width is modulated as the star rotates is diluted.
---------------------------------------------------------
Title: Magnetic loops on rapidly rotating stars.
Authors: Unruh, Y. C.; Jardine, M.
1997A&A...321..177U Altcode:
We present models for the thermal and mechanical equilibria of slender
magnetic loops on rapidly-rotating stars. These loops are embedded
within an arcade located on the stellar equator. The loop properties
are governed principally by the specified base pressure and conductive
flux. While rapid rotation is important in determining the pressure
structure within the loop, its main effect on the loop shape is through
its influence on the base values of magnetic field strength, pressure,
and conductive flux. We have compared our models with observations of
the temperatures and X-ray fluxes of stars with a range of rotation
rates. By using the observed variation of the differential emission
measure with rotation rate {OMEGA} and allowing the base magnetic
field strength to scale as B {prop.to}{OMEGA}^q^ (q=0.5,0.75,1.0)
we can explain the variation of the temperature and X-ray flux of the
slower rotators. For the most rapid rotators, however (approximately
{OMEGA}/{OMEGA}<SUB>sun</SUB>_>10) it appears that a single value of
q for all rotation rates cannot explain the observations and some other
mechanism is needed to explain the saturation in the X-ray flux. We
have also investigated the effect of using a heating function that is
proportional to the density and one that falls off exponentially with
height. With the parameters that we can calculate from these models
it is not possible to discriminate between these two types of heating.
---------------------------------------------------------
Title: Reliability tests for Doppler imaging
Authors: Unruh, Y. C.
1996IAUS..176...35U Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Evolution of Surface Structures on Ab-Doradus
Authors: Unruh, Y. C.; Collier Cameron, A.; Cutispoto, G.
1995MNRAS.277.1145U Altcode:
We present the third set of a long-term series of Doppler images of
the starspot distribution on AB Doradus, a rapidly rotating active
K0 dwarf. The images were obtained from simultaneous spectroscopic
and photometric observations taken on the Anglo-Australian Telescope
and the European Southern Observatory in 1993 November. Our images
show two active latitudes, a low-latitude band producing most of the
photometric modulation, and a high-latitude band centred at 60°. The
spot distribution at low latitudes is very stable and persists over 5
stellar rotations. It is also remarkably similar to the distribution
found in 1992 December. The high-latitude structure is more variable
and seems to change on the order of a few rotation periods. In
agreement with measurements from 1992 January, we find no indication
for differential rotation on AB Doradus.
---------------------------------------------------------
Title: The sensitivity of Doppler imaging to line profile models
Authors: Unruh, Y. C.; Collier Cameron, A.
1995MNRAS.273....1U Altcode:
In recent years there have been a number of successful reconstructions
of the surfaces of fast rotating stars using Doppler imaging. As a
large proportion of the imaged stars show large high-latitude spots,
some doubt remains as to whether these high-latitude spots might be
artefacts. In this paper we investigate how sensitive Doppler imaging
is to the exact shape of the mapping line profile and its variation as
a function of limb angle. We find that Doppler imaging is surprisingly
robust against errors in the limb dependence of the profile, but that
errors in the shape of the profile, and in particular the neglect of
blends at considerable distances from the mapping line, will lead to
spurious banding in the reconstructed images.
---------------------------------------------------------
Title: Surface structures on young solar-type stars.
Authors: Collier Cameron, A.; Unruh, Y. C.
1995mscs.conf..201C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Surface structure on DF Tau
Authors: Unruh, Y. C.; Collier-Cameron, A.; Guenther, E.
1995IAUS..176P..93U Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Doppler images of AB Doradus in 1992 January.
Authors: Collier Cameron, A.; Unruh, Y. C.
1994MNRAS.269..814C Altcode:
We present a set of maximum entropy reconstructions of the starspot
distribution on the surface of the rapidly rotating KO dwarf AB
Doradus. The images were obtained from three independent data
sets secured on three consecutive nights of observation at the
Anglo-Australian Telescope in 1992 January. We discuss the effects of
several potential types of systematic error in Doppler imaging, and
methods of eliminating them. Independent reconstructions are presented
in the three photo spheric lines: Ca I 643.9 nm, Fe I 666.3 nm and Ca
I 671.8 nm. All the images indicate a bimodal latitude distribution of
spot area coverage, with a broad low-latitude band and a circumpolar
`crown'. The gross azimuthal structures in the polar crown and the
low-latitude band show no evidence of longitude shifts over the
duration of the observing run. On the time-scale of a single stellar
rotation the star's surface layers thus appear to be in a state of
nearly solid-body rotation. Key words: techniques: image processing -
stars: activity - stars: atmospheres - stars: individual: AB Dor -
stars: magnetic fields - stars: rotation.
---------------------------------------------------------
Title: Doppler imaging of late-type stars
Authors: Unruh, Y. C.
1994PhDT........12U Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Sensitivity of Doppler Imaging to Errors in the Line
Profile Shape
Authors: Unruh, Yvonne C.; Collier Cameron, Andrew
1994ASPC...64..667U Altcode: 1994csss....8..667U
No abstract at ADS
---------------------------------------------------------
Title: Doppler imaging of late-type stars
Authors: Unruh, Yvonne Christine
1994PhDT........15U Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Photospheric inhomogeneities on cool stars
Authors: Collier Cameron, A.; Jeffery, C. S.; Unruh, Y. C.
1992sccw.conf...81C Altcode:
No abstract at ADS