The role of quantum interference and partial redistribution in the solar Ba II D2 4554 A line

TL;DR

This paper investigates the polarization profiles of the Ba II D2 line at 4554 Å, emphasizing the importance of quantum interference, isotope contributions, and partial frequency redistribution in accurately modeling observed solar polarization.

Contribution

It introduces radiative transfer modeling with partial frequency redistribution to accurately reproduce the line's polarization profiles, highlighting the limitations of complete redistribution models.

Findings

PRD is essential for modeling the line's wing polarization.

Theoretical profiles vary significantly with limb distance and atmospheric model.

Complete redistribution cannot reproduce observed polarization profiles.

Abstract

The Ba II D2 line at 4554 A is a good example, where the F-state interference effects due to the odd isotopes produce polarization profiles, which are very different from those of the even isotopes that do not exhibit F-state interference. It is therefore necessary to account for the contributions from the different isotopes to understand the observed linear polarization profiles of this line. In this paper we present radiative transfer modeling with partial frequency redistribution (PRD), which is shown to be essential to model this line. This is because complete frequency redistribution (CRD) cannot reproduce the observed wing polarization. We present the observed and computed Q/I profiles at different limb distances. The theoretical profiles strongly depend on limb distance (\mu) and the model atmosphere which fits the limb observations fails at other \mu\ positions.