Tese de Doutorado #087: Sílvia Alencar

We initially investigate some processes that affect the stellar atmosphere, such as the gravity-brightening and limb-darkening, and the influence of the reflection effect on them. We study the gravity-brightening exponents using the Uppsala Model Atmospheres. In non-illuminated convective atmospheres the exponent value (beta=0.32) proposed by Lucy was confirmed only for T_eff close to 6500 K. The exponent depends upon T_eff, being rather insensitive to variations of the mixing-length parameter, the stellar mass and the use of grey or non-grey atmospheres. We demonstrate the influence of the mutual illumination in a close binary on the gravity-brightening exponent. The external illumination increases the value of beta, the larger the amount of incident flux the larger the value of the exponent. This effect is caused by the “quenching” of convection as the external illumination heats the surface layers of the illuminated star, bringing it closer to radiative equilibrium, where beta is close to unity.