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Astron. Astrophys. 326, 257-262


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The gravity-brightening effect and stellar atmospheres

I. Results for models with 3700 K < Teff < 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 ( FORMULA ) 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 3700 K < Teff < 7000 K. The value FORMULA =0.32 proposed by Lucy was confirmed only for Teff ~ 6500 K. FORMULA depends upon Teff (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 FORMULA values in eclipsing binary light curve analysis are presented. A dependence of FORMULA on external illumination (''reflection effect'') for convective models is evidenced for the first time, the larger the amount of incident flux the larger the FORMULA exponent.

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

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


© European Southern Observatory (ESO) 1997

Online publication: September 9, 1997
Last change: April 20, 1998
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