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

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The gravity-brightening effect and stellar atmospheres

I. Results for models with 3700 K [FORMULA] [FORMULA] [FORMULA] 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 [FORMULA] [FORMULA] [FORMULA]. The value [FORMULA] =0.32 proposed by Lucy was confirmed only for [FORMULA] K. [FORMULA] depends upon [FORMULA] (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

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© European Southern Observatory (ESO) 1997

Online publication: April 20, 1998
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