Astron. Astrophys. 326, 257-262 (1997)

The gravity-brightening effect and stellar atmospheres

I. Results for models with 3700 K 7000 K

S.H.P. Alencar and L.P.R. Vaz

Departamento de Física-ICEx-UFMG, Caixa Postal 702, 30.161-970 Belo Horizonte MG, Brazil

Received 8 August 1996 / Accepted 18 March 1997

Abstract

The gravity-brightening exponent () is studied using the UMA (Uppsala Model Atmosphere) code in non-illuminated convective grey (in the sense of "continuum only" opacity) and non-grey (line blanketed) atmospheres, for . The value =0.32 proposed by Lucy was confirmed only for K. depends upon (an analytical expression is given), being rather insensitive to variations of the mixing length parameter, of the stellar mass and to the use of grey or non-grey atmospheres. A comparison with empirical determinations and a preliminary test of the use of the proposed values in eclipsing binary light curve analysis are presented. A dependence of on external illumination ("reflection effect") for convective models is evidenced for the first time, the larger the amount of incident flux the larger the exponent.

Key words: atmospheres stars: binaries: close stars: binaries: eclipsing stars: fundamental parameters stars: general

Send offprint requests to: L.P.R. Vaz

Contents

• 1. Introduction
  • 1.1. Basic works on the gravity-brightening effect
  • 1.2. Empirical determinations and modern works
• 2. The atmosphere model
  • 2.1. The method
  • 2.2. Convective grey (continuum only) atmospheres
  • 2.3. Convective non-grey (line blanketed) atmospheres
• 3. Discussion
  • 3.1. Comparison with empirical determinations
  • 3.2. One first observational test
• 4. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1997

Online publication: April 20, 1998
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