Simultaneous Spectropolarimetric Observations in the Hα and Ca ii 8662 Å Lines of an Active Region

Abstract

We present spectropolarimetric observations of an active region recorded simultaneously in the H α and the Ca ii 8662 Å lines. The sunspot exhibits multiple structures, including a light bridge and a region where the Ca ii 8662 Å line core is in emission. Correspondingly, the H α 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 nonlocal thermodynamic equilibrium multiline inversions of the Ca ii 8662 Å line and the weak field approximation (WFA) over the H α line. The field strength inferred from the H α line core is consistently smaller than that inferred from inversions at $\mathrm{log}{\tau }_{500}$ = −4.5. However, the study finds no correlation between the WFA over the core of the H α line and that inferred from inversions at $\mathrm{log}{\tau }_{500}$ = −4.5. In regions exhibiting emission features, the morphology of the magnetic field at $\mathrm{log}{\tau }_{500}$ = −4.5 resembles that at $\mathrm{log}{\tau }_{500}$ = −1, with slightly higher or comparable field strengths. The magnetic field morphology inferred from the core of the H α line is also similar to that inferred from the full spectral range of the H α line in the emission region. The field strength inferred in the light bridge at $\mathrm{log}{\tau }_{500}$ = −1 is smaller than the surrounding umbral regions and comparable at $\mathrm{log}{\tau }_{500}$ = −4.5. Similarly, the field strength inferred in the light bridge from the WFA over the H α line appears lower compared to the surrounding umbral regions.

Keywords

• Solar photosphere
• Solar chromosphere
• Solar magnetic fields