Radiative transfer in the distorted and irradiated atmospheres of close binary components

Abstract

We studied the transfer of line radiation in the distorted and expanding atmospheres of close binary components. We assumed that the distortion of the atmosphere is caused by self rotation and tidal force exerted by the presence of the secondary component. The distortion is measured in terms of the ratio of angular velocities at the equator and pole (X), mass ratio of the two components (m2)/(m1), the ratio of centrifugal force to that of gravity at the equator of the primary (f) and ratio of the equatorial radius of the primary to the distance between the centres of gravity of the two components displaystyle (re)/(R). A seventh degree equation is obtained to describe the distorted surface in terms of the above mentioned parameters. We have used X=1 for uniform rotation throughout and used values f=0.1 and 0.5, (m2)/(m1)=1, and (re)/(R)=0.1, 0.3, and 0.5. The equation of line transfer is solved in the comoving frame of the expanding atmosphere of the primary using complete redistribution in the line. We used a linear law of velocity of expansion so that the density varies as r-3 where r is the radius of the star, satisfying the law of conservation of mass. We set va=0 and vb=10 mtu (mean thermal units) where va is the velocity at the surface of the primary with radius r=a(=5*E11) cm and vb is the velocity at the surface of the extended atmosphere with radius r=b(=1012) cm. We also computed lines in a static atmosphere with density changing as rho ~ r-1. We have considered a primary with an effective temperature T* and a point source of secondary with three different temperatures Tc equal to 2x 104 K, 3x 104 K, and 4x 104 K. The maximum change in line fluxes is noticed when the parameters (re)/(R) and f are changed, while the changes due to (m2)/(m1) are minimal. The expansion of the atmosphere produces P Cygni type line profiles. The incident radiation from the secondary increases the line fluxes and absorption in the centre of the line is replaced by emission.