Polarized line formation with incomplete Paschen-Back effect and partial frequency redistribution

Abstract

Quantum interference between the hyperfine structure states is known to depolarize the cores of some of the lines in the linearly polarized spectrum of the Sun (the Second Solar Spectrum). The presence of external magnetic fields in the line forming regions modify these signatures through the Hanle, Zeeman, and incomplete/ complete Paschen-Back effects (PBE), depending on the strength of the magnetic field. In an earlier paper, Sowmya et al. (2014) derived the relevant collisionless partial frequency redistribution (PFR) matrix for scattering on a two-level atom with hyperfine structure splitting (HFS) and in the presence of arbitrary strength magnetic fields (including the PBE regime). In the present paper we solve the problem of polarized line transfer in a magnetized atmosphere, including this PFR matrix. For this purpose, we apply a scattering expansion method which is based on orders of scattering approach. We present the results on the combined effects of PBE and PFR on the polarized line profiles using the atomic parameters relevant to the Na I D2 line