Tests of stellar model atmospheres by optical interferometry

Wittkowski, M.; Aufdenberg, J. P.; Driebe, T.; Roccatagliata, V.; Szeifert, T.; Wolff, B.

doi:10.1051/0004-6361:20066032

Cited by 30 publications

(29 citation statements)

References 44 publications

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“…This result is consistent with the similar observations of the RSG VY CMa by Wittkowski et al (2012) and the results shown by Lançon et al (2007). The satisfactory fit to stellar spectra, together with an unsatisfactory fit to interferometric visibilities, illustrates the importance of interferometric observations in addition to spectral observations to fully constrain and test stellar model atmospheres, as noted previously by, e.g., Wittkowski et al (2006) and Paladini et al (2011). In a future work, it may be possible to extend PHOENIX model atmospheres farther out, for instance by attaching a slow wind to the atmosphere, or by considering NLTE in the molecular lines or 3D structures.…”

Section: Atmospheric Structuresupporting

confidence: 92%

The atmospheric structure and fundamental parameters of the red supergiants AH Scorpii, UY Scuti, and KW Sagittarii

Arroyo-Torres

Wittkowski²,

Marcaide

et al. 2013

A&A

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Aims. We present the atmospheric structure and the fundamental properties of the red supergiants (RSGs) AH Sco, UY Sct, and KW Sgr based on VLTI/AMBER observations. Methods. We carried out spectro-interferometric observations of AH Sco, UY Sct, and KW Sgr in the near-infrared K band (1.92-2.47 μm) with the VLTI/AMBER instrument with spatial and spectral resolutions of 3 milliarcsec and 1500, respectively, and compared the data to a new grid of hydrostatic PHOENIX model atmospheres.Results. In our visibility data, we observe molecular layers of water and CO in extended atmospheres. For a uniform disk modeling, we observe size increases at the water band centered at 1.9 μm of 10% to 25% and at the CO bandheads at 2.3-2.5 μm of 20%-35% with respect to the near-continuum bandpass at around 2.20 μm. Our near-infrared spectra of AH Sco, UY Sct, and KW Sgr are well reproduced by the PHOENIX model atmospheres. The continuum visibility values are consistent with a limb-darkened disk as predicted by the PHOENIX models. However, the model visibilities do not predict the large observed extensions of the molecular layers. Comparing the continuum visibility values to PHOENIX models, we estimate the Rosseland-mean photospheric angular diameters of AH Sco, UY Sct, and KW Sgr to be 5.81 ± 0.15 mas, 5.48 ± 0.10 mas, and 3.91 ± 0.25 mas, respectively. Together with the distance and the spectro-photometry, we calculate radii of 1411 ± 124 R for AH Sco, 1708 ± 192 R for UY Sct, and 1009 ± 142 R for KW Sgr and effective temperatures of 3682 ± 190 K for AH Sco, 3365 ± 134 K for UY Sct, and 3720 ± 183 K for KW Sgr. Conclusions. AH Sco, UY Sct, and KW Sgr exhibit extended atmospheric layers of H 2 O and CO. The PHOENIX atmosphere models predict the spectra and the continuum visibility values, but cannot reproduce the large extensions of the molecular layers. This indicates that the opacities of the molecular bands are included, but that the model atmospheres are too compact compared to the observations. The observed extended layers may be levitated by processes such as pulsation or convection, which are not included in the hydrostatic atmospheric models. The location of the targets in the HR-diagram is confirmed to be close to, and possibly slightly to the right of, the Hayashi limit of recent evolutionary tracks corresponding to masses between about 20 M and 40 M .

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Section: Atmospheric Structuresupporting

confidence: 92%

The atmospheric structure and fundamental parameters of the red supergiants AH Scorpii, UY Scuti, and KW Sagittarii

Arroyo-Torres

Wittkowski²,

Marcaide

et al. 2013

A&A

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“…demonstrated that model stellar atmospheres computed with this code predict temperature structures consistent with planeparallel ATLAS9 and ATLAS12 models as well as spherically symmetric PHOENIX ) and MARCS (Gustafsson et al 2008) models. Furthermore, showed that spherical model atmospheres predict intensity distributions that fit interferometric observations of red giant stars (Wittkowski et al 2004(Wittkowski et al , 2006a with center-to-limb intensity profiles from model atmospheres, and they determined stellar parameters consistent with results using ATLAS9 and PHOENIX models.…”

Section: A3mentioning

confidence: 55%

“…The angular diameter of α Cet was determined by Wittkowski et al (2006a) from long-baseline interferometry, using the same instrumentation as for α Tau, and taking into account limb darkening. The same authors also determined F bol from integrated absolute flux measurements.…”

Section: α Cetmentioning

confidence: 99%

Comparative modelling of the spectra of cool giants

Lebzelter¹,

Heiter²,

Abia³

et al. 2012

A&A

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Context. Our ability to extract information from the spectra of stars depends on reliable models of stellar atmospheres and appropriate techniques for spectral synthesis. Various model codes and strategies for the analysis of stellar spectra are available today. Aims. We aim to compare the results of deriving stellar parameters using different atmosphere models and different analysis strategies. The focus is set on high-resolution spectroscopy of cool giant stars. Methods. Spectra representing four cool giant stars were made available to various groups and individuals working in the area of spectral synthesis, asking them to derive stellar parameters from the data provided. The results were discussed at a workshop in Vienna in 2010. Most of the major codes currently used in the astronomical community for analyses of stellar spectra were included in this experiment.Results. We present the results from the different groups, as well as an additional experiment comparing the synthetic spectra produced by various codes for a given set of stellar parameters. Similarities and differences of the results are discussed. Conclusions.Several valid approaches to analyze a given spectrum of a star result in quite a wide range of solutions. The main causes for the differences in parameters derived by different groups seem to lie in the physical input data and in the details of the analysis method. This clearly shows how far from a definitive abundance analysis we still are.Key words. stars: atmospheres -stars: late-type -stars: abundances -stars: fundamental parameters Based on observations obtained at the Bernard Lyot Telescope (TBL, Pic du Midi, France) of the Midi-Pyrénées Observatory, which is operated by the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France.Tables 6-11 are only available in electronic form at http://www.aanda.orgThe spectra of stars 1 to 4 used in the experiment presented here are only availalbe at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via

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“…We prefer the values by Kervella et al (2008) because van Belle & von Braun (2009) derived a significant extinction for the K7V component (A V = 0.23 ± 0.01 mag, while A V = 0 for the K5V component as expected for this nearby system), and their angular diameter for the K7V component is larger than that of the K5V component (although they are equal within the uncertainties). Limb darkening was taken into account using individual atmospheric models in the cases of ψ Phe, α Cet, and γ Sge (Wittkowski et al 2004(Wittkowski et al , 2006a, for which spherical PHOENIX models (Hauschildt & Baron 1999, version 13) were computed. In the case of Procyon, α Cen B, and HD 122563, 3D-RHD simulations were applied by Chiavassa et al (2012), Bigot et al (2006), and Creevey et al (2012), respectively.…”

Section: Angular Diametersmentioning

confidence: 99%

GaiaFGK benchmark stars: Effective temperatures and surface gravities

Heiter

Jofré

Gustafsson

et al. 2015

A&A

287

414

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Context. In the era of large Galactic stellar surveys, carefully calibrating and validating the data sets has become an important and integral part of the data analysis. Moreover, new generations of stellar atmosphere models and spectral line formation computations need to be subjected to benchmark tests to assess any progress in predicting stellar properties. Aims. We focus on cool stars and aim at establishing a sample of 34 Gaia FGK benchmark stars with a range of different metallicities. The goal was to determine the effective temperature and the surface gravity independently of spectroscopy and atmospheric models as far as possible. Most of the selected stars have been subjected to frequent spectroscopic investigations in the past, and almost all of them have previously been used as reference, calibration, or test objects. Methods. Fundamental determinations of T eff and log g were obtained in a systematic way from a compilation of angular diameter measurements and bolometric fluxes and from a homogeneous mass determination based on stellar evolution models. The derived parameters were compared to recent spectroscopic and photometric determinations and to gravity estimates based on seismic data. Results. Most of the adopted diameter measurements have formal uncertainties around 1%, which translate into uncertainties in effective temperature of 0.5%. The measurements of bolometric flux seem to be accurate to 5% or better, which contributes about 1% or less to the uncertainties in effective temperature. The comparisons of parameter determinations with the literature in general show good agreements with a few exceptions, most notably for the coolest stars and for metal-poor stars. Conclusions. The sample consists of 29 FGK-type stars and 5 M giants. Among the FGK stars, 21 have reliable parameters suitable for testing, validation, or calibration purposes. For four stars, future adjustments of the fundamental T eff are required, and for five stars the log g determination needs to be improved. Future extensions of the sample of Gaia FGK benchmark stars are required to fill gaps in parameter space, and we include a list of suggested candidates.

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Tests of stellar model atmospheres by optical interferometry

Cited by 30 publications

References 44 publications

The atmospheric structure and fundamental parameters of the red supergiants AH Scorpii, UY Scuti, and KW Sagittarii

The atmospheric structure and fundamental parameters of the red supergiants AH Scorpii, UY Scuti, and KW Sagittarii

Comparative modelling of the spectra of cool giants

GaiaFGK benchmark stars: Effective temperatures and surface gravities

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