Polarized radiation from hot plasmas and applications to AM herculis binaries. II. Effect of collisions and thomson scattering

The absorption coefficients in the ordinary and extraordinary modes are calculated, for radiation emitted by magnetoactive plasmas with temperatures in the range 0.1--5 keV. The equations of radiative transfer for a homogeneous plasma, with large Faraday rotation, are solved, and simple analytic expressions for the Stokes parameters Q and V are derived in terms of the optical depths in the ordinary and extraordinary modes. The results are applied to homogeneous plasma slabs which represent a simple model for the accretion columns of the AM Herculis binaries. It is shown that the inclusion of the effects of collisions and Thomson scattering reduces the amount of fractional polarized radiation, bringing better agreement with observations. For small viewing angles with the magnetic field the circular polarization does not approach 100% as in the collisionless case, but instead approaches 0% or a value less than 100% depending on the geometry. This may provide a qualitative explanation for the standstills observed in some AM Her binaries