Resonance line polarization in spherical atmospheres: Partial redistribution effects studied with the Domke-Hubeny redistribution matrix

Abstract

The problem of resonance line polarization including collisional redistribution is studied using simple theoretical models. The medium is assumed to be a static finite spherical shell atmosphere. The purpose of this paper is to understand the behavior of line polarization when elastic and inelastic collisions cause frequency redistribution upon scattering. All the redistribution mechanisms that are astrophysically relevant are considered in a simple two-level atom picture. The dependence of resonance line polarization on physical parameters of the two-level atom formulation and on the collisional parameters is shown in detail. The Domke-Hubeny generalized collisional redistribution matrix for polarized radiation is employed in most of the examples shown in this paper. It is shown that different types of collisions that affect photon redistribution in both resonance and subordinate lines can be distinguished through the characteristic changes they produce in the intensity and linear polarization profiles. The simple asymptotic expressions of partial redistribution theory are shown to be useful in the interpretation of model intensity and polarization profiles.