Astron. Astrophys. 364, 137-156 (2000)

ISO-SWS calibration and the accurate modelling of cool-star atmospheres

I. Method ^*

L. Decin ^{**  1}, C. Waelkens ¹, K. Eriksson ², B. Gustafsson ², B. Plez ³, A.J. Sauval ⁴, W. Van Assche ^{***  5} and B. Vandenbussche <sup>1

1</sup> Instituut voor Sterrenkunde, KULeuven, Celestijnenlaan 200B, 3001 Leuven, Belgium
² Astronomiska Observatoriet, Box 515, 75120 Uppsala, Sweden
³ GRAAL - CC72, Université de Montpellier II, 34095 Montpellier Cedex 5, France
⁴ Observatoire Royal de Belgique, Avenue Circulaire 3, 1180 Bruxelles, Belgium
⁵ Instituut voor Wiskunde, KULeuven, Celestijnenlaan 200B, 3001 Leuven, Belgium

Received 29 November 1999 / Accepted 3 August 2000

Abstract

A detailed spectroscopic study of the ISO-SWS data of the red giant Tau is presented, which enables not only the accurate determination of the stellar parameters of Tau, but also serves as a critical review of the ISO-SWS calibration.

This study is situated in a broader context of an iterative process in which both accurate observations of stellar templates and cool star atmosphere models are involved to improve the ISO-SWS calibration process as well as the theoretical modelling of stellar atmospheres. Therefore a sample of cool stars, covering the whole A0 - M8 spectral classification, has been observed in order to disentangle calibration problems and problems in generating the theoretical models and corresponding synthetic spectrum.

By using stellar parameters found in the literature large discrepancies were seen between the ISO-SWS data and the generated synthetic spectrum of Tau. A study of the influence of various stellar parameters on the theoretical models and synthetic spectra, in conjunction with the Kolmogorov-Smirnov test to evaluate objectively the goodness-of-fit, enables us to pin down the stellar parameters with a high accuracy:  K, g, M , z  dex, , , (C)  dex, (N)  dex, (O)  dex and mas. These atmospheric parameters were then compared with the results provided by other authors using other methods and/or spectra.

Key words: stars: atmospheres stars: fundamental parameters stars: individual: Alpha Tau stars: late-type infrared: stars

* Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA.
** Scientific researcher of the Fund for Scientific Research, Flanders
*** Research Director of the Fund for Scientific Research, Flanders

Send offprint requests to: L. Decin

Correspondence to: Leen.Decin@ster.kuleuven.ac.be

SIMBAD Objects

Contents

• 1. Introduction
• 2. Observations and data reduction
• 3. Literature study: Tau
• 4. Influence of stellar parameters on synthetic spectra
  • 4.1. Models
  • 4.2. Effect of changing the effective temperature
  • 4.3. Effect of changing the gravity and the mass
  • 4.4. Effect of changing the metallicity
  • 4.5. Effect of changing the microturbulent velocity
  • 4.6. Effect of changing the isotopic ratio
  • 4.7. Effect of changing (C), (N) or (O)
• 5. Method of analysis
• 6. Discussion
• 7. Conclusions
• Acknowledgements
• Appendices
  • A: Comments on the different stellar parameters of Tau
  • B: The approximate absorption coefficient
• References

© European Southern Observatory (ESO) 2000

Online publication: December 15, 2000
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