Collisional redistribution effects on line polarization in spherical atmospheres

Abstract

The polarization of resonance and subordinate lines formed in spherically symmetric media is studied. The effect of collisions is shown by taking a combination of partial redistribution mechanisms represented by the functions R_II-A(x,x'') and R_III-A(x,x''), which are well-known redistribution functions that describe interaction of line photons with a two-level model atom. A large number of models are presented, which clearly show the effect of collisions on line polarization, when basic model parameters of a two-level atom are varied one at a time. Thus the grid of models generated serves to establish upper and lower limits on the impact of collisions on line polarization. Some results employing a more accurate treatment of collisional redistribution are also shown. The purpose of this paper is to understand the quantitative behaviour of line polarization when collisional redistribution plays an important role in the transfer of line radiation.