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

Abstract

We present spectropolarimetric observations of an active region recorded simultaneously in the H$\alpha$ Ca II 8662 Å lines. The sunspot exhibits multiple structures, including a lightbridge and a region where Ca II 8662 Å 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 Å 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.

arXiv commentaccepted to be published in ApJ on 4th June, 2024, 14 pages, 7 figures

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