Polarized Line Formation in Arbitrary Strength Magnetic Fields: the case of a two-level atom with hyperfine structure splitting

TL;DR

This paper develops a comprehensive model for polarized line formation in magnetized atmospheres, accounting for quantum interference, partial frequency redistribution, and hyperfine structure effects, with applications to solar spectral lines.

Contribution

It introduces a novel solution to polarized line transfer considering hyperfine structure, PFR, and arbitrary magnetic fields using the scattering expansion method.

Findings

Paschen-Back effect significantly alters polarized line profiles.

Hyperfine structure influences the polarization signatures in spectral lines.

The model successfully reproduces observed features in Li I and Na I D2 lines.

Abstract

Quantum interference effects together with partial frequency redistribution (PFR) in line scattering produce subtle signatures in the so called Second Solar Spectrum (the linearly polarized spectrum of the Sun). These signatures are modified in the presence of arbitrary strength magnetic fields via the Hanle, Zeeman, and Paschen-Back effects. In the present paper we solve the problem of polarized line formation in a magnetized atmosphere taking into account scattering in a two-level atom with hyperfine structure splitting together with PFR. To this end we incorporate the collisionless PFR matrix derived in Sowmya et al. (2014) in the polarized transfer equation. We apply the scattering expansion method to solve this transfer equation. We study the combined effects of PFR and Paschen-Back effect on polarized line profiles formed in an isothermal one-dimensional planar atmosphere. For this purpose, we consider the cases of D$_2$ lines of Li\,{\sc i} and Na\,{\sc i}.