Simultaneous spectropolarimetric observations in the H$\alpha$ and Ca II 8662 {\AA} lines of an active region

TL;DR

This study presents simultaneous spectropolarimetric observations of an active solar region in Hα and Ca II 8662 Å lines, analyzing magnetic field stratification and morphology through inversions and approximations.

Contribution

It provides a detailed comparison of magnetic field inferences from Hα and Ca II lines, highlighting differences and similarities in magnetic field strength and morphology in active region structures.

Findings

Hα line core magnetic field strength is smaller than that from Ca II inversions.

No correlation between WFA over Hα core and inversion results at log τ = -4.5.

Magnetic field morphology in emission regions resembles that at different optical depths.

Abstract

We present spectropolarimetric observations of an active region recorded simultaneously in the H$\alpha$ Ca II 8662 {\AA} lines. The sunspot exhibits multiple structures, including a lightbridge and a region where Ca II 8662 {\AA} line core is in emission. Correspondingly, the H$\alpha$ line core image displays brightening in the emission region, with the spectral profiles showing elevated line cores. The stratification of the line-of-sight magnetic field is inferred through non-LTE multiline inversions of the Ca II 8662 {\AA} line and the weak field approximation over the H$\alpha$ line. The field strength inferred from the H$\alpha$ line core is consistently smaller than that inferred from inversions at $\log \tau_{500}$ = $-$4.5. However, the study finds no correlation between the WFA over the core of the H$\alpha$ line and that inferred from inversions at $\log \tau_{500}$ = $-$4.5. In regions exhibiting emission features, the morphology of the magnetic field at $\log \tau_{500}$ = $-$4.5 resembles that at $\log \tau_{500}$ = $-$1, with slightly higher or comparable field strengths. The magnetic field morphology inferred from the core of the H$\alpha$ line is also similar to that inferred from the full spectral range of the H$\alpha$ line in the emission region. The field strength inferred in the lightbridge at $\log \tau_{500}$ = $-$1 is smaller than the surrounding umbral regions and comparable at $\log \tau_{500}$ = $-$4.5. Similarly, the field strength inferred in the lightbridge from the WFA over the H$\alpha$ line appears lower compared to the surrounding umbral regions.