Atmospheres of components of the close binary stars

Abstract

For theoretical modeling of binary systems, one has to consider realistic models which takes into account the radiative transfer, hydrodynamics, and the effect of irradiation from the secondary component on the atmosphere of primary component. Since the problem is complex, we studied in the thesis idealized models which will help us in understanding the important physical processes in close binaries. As a first step to understand the reflection effect we have developed a method of obtaining radiation field from the spherical surface irradiated by an external (i) point source (ii) extended source of radiation in close binary systems. The method has been extended in the case of atmospheres distorted due to self rotation of the component and tidal effects due to the presence of its companion. In all the cases we used two-level atom approximation with complete redistribution in calculating the spectral lines formed in the atmosphere of the primary star. The effects of irradiation from the secondary component on the atmosphere of the primary is calculated depending upon the geometrical shape of the illuminated surface, proximity of the secondary component to the primary and ratio of the luminosities of the primary and the secondary. We calculated the line profiles with various parameters like density and velocity variations. We notice that the expansion of the medium produces P Cygni type profiles and the irradiation enhances the emission in the lines although the equivalent widths reduce considerably. In the case of rotationally distorted star without tidal forces we find the radiation to be diluted. Close binary systems with tidal distortion produce emission profiles filling the self absorption from the primary component.