Rigorous treatment of the radiative transfer problem in stellar winds - Significance of the velocity law and the chromosphere in the H-alpha profile

Abstract

We have computed H-alpha line profiles with the aim of contributing to the diagnosis of the atmospheric structure in Be-type stars. We consider an expanding atmosphere with a chromospheric temperature distribution. The simultaneous solution of the statistical equilibrium equations was carried out for a hydrogen atomic model considering six energy levels plus continuum. After computing 90 models with different effective temperatures, and velocity and temperature laws, we conclude that the morphological characteristics of the H-alpha profile (P Cygni, double-peaked, or single-peaked emission) are strongly determined by the structure of the wind in the atmospheric layers close to the central star (the base of the wind and the immediate subphotospheric regions) rather than in the cool envelope. Our models indicate that the cool envelope only contributes to the global intensity of the H-alpha emission profile. These results provide an alternative interpretation of the Be phenomenon, in terms of the source function behavior.