Effects of high radial velocities on line transfer in extended atmospheres

Abstract

The equation of radiative transfer in a comoving frame has been solved for rapidly expanding gaseous medium in spherically symmetric extended stellar atmospheres. A non-LTE two-level atom with Voigt profile function is assumed. The comoving terms in the radiative transfer are discretized in the framework of the discrete space theory of Grant. These terms are simply reduced to a tri-diagonal matrix. The boundary conditions for the frequency derivative can be introduced through the elements of the first and last rows of this matrix. This seems to be quite stable for arbitrary velocities in the medium. Maximum velocities up to 60 units of mean thermal velocities have been considered.