Application of the etla approach in the comoving frame to the study of winds in hot stars

Abstract

Among the various methods developed for studying the formation of line profiles in an expanding atmosphere, the one based on the direct solution of the coupled comoving-frame transfer and statistical equilibrium equations with multilevel, multi-ion model atoms in the equivalent-two-level-atom (ETLA) scheme (Mihalas and Kunasz, 1978), offers particular advantages over other methods. It handles correctly the transonic wind region and converges relatively easily. We have adapted a version of this code extensively used by one of us for Herbig AeBe stars (e.g. Catala and Kunasz, 1987), for application to hot stars. Appending a wind model to a photosphere calculated with the non-LTE TLUSTY code of Hubeny (1989), we have computed the CIV line profiles in a test case calculated by Pauldrach et al. (1990) with the entirely different technique, called “unified atmosphere-wind theory”. The effect of the turbulence across the winds appears to be important to reproduce observed profiles in hot stars.