J-state interference signatures in the Second Solar Spectrum: Modeling the Cr I triplet at 5204-5208 A

TL;DR

This study demonstrates that including J-state interference and partial frequency redistribution in modeling the Cr I triplet's polarization is essential for accurately reproducing observed solar spectrum features, revealing the triplet's sensitivity to photospheric temperature structures.

Contribution

It introduces a comprehensive modeling approach that incorporates J-state interference and partial frequency redistribution effects for the first time in analyzing the Cr I triplet in the Second Solar Spectrum.

Findings

J-state interference significantly affects polarization signatures.

Partial frequency redistribution improves model-data agreement.

Temperature adjustments are needed for accurate wing polarization modeling.

Abstract

The scattering polarization in the solar spectrum is traditionally modeled with each spectral line treated separately, but this is generally inadequate for multiplets where J-state interference plays a significant role. Through simultaneous observations of all the 3 lines of a Cr I triplet, combined with realistic radiative transfer modeling of the data, we show that it is necessary to include J-state interference consistently when modeling lines with partially interacting fine structure components. Polarized line formation theory that includes J-state interference effects together with partial frequency redistribution for a two-term atom is used to model the observations. Collisional frequency redistribution is also accounted for. We show that the resonance polarization in the Cr I triplet is strongly affected by the partial frequency redistribution effects in the line core and near wing peaks. The Cr I triplet is quite sensitive to the temperature structure of the photospheric layers. Our complete frequency redistribution calculations in semi-empirical models of the solar atmosphere cannot reproduce the observed near wing polarization or the cross-over of the Stokes Q/I line polarization about the continuum polarization level that is due to the J-state interference. When however partial frequency redistribution is included, a good fit to these features can be achieved. Further, to obtain a good fit to the far wings, a small temperature enhancement of the FALF model in the photospheric layers is necessary.