Radiative transfer in the dusty, irradiated expanding atmospheres of close binary components

Abstract

We studied the formation of lines in the irradiated expanding dusty atmospheres of the components of close binary systems. We considered a two-level atom approximation in Non-LTE situation with complete redistribution. The thickness of the atmosphere is set to be equal to twice that of the stellar radius. Maximum expansion velocities is set to be as large as 50 mean thermal units. The isotropically scattering dust is distributed uniformly in the atmosphere. We have computed the lines using a total optical depths 104 at the line centre. The irradiation from the secondary is one, five and ten times the self radiation. The line fluxes in the line of sight are calculated by using the total source function which is the sum of the source functions due to self radiation and that due to irradiation from the secondary. The line profiles formed in dusty atmosphere are compared with those formed in dust free atmosphere. The profiles are presented for different velocities of expansion, different separations between the components and several dust optical depths. P Cygni type profiles are produced in the expanding atmosphere and the irradiation from the secondary enhances the emission in the lines. The major effect of dust on the formation of lines in the expanding atmospheres of the component of close binary is to scatter photons into the line core, among others.