Inference of chromospheric magnetic fields in a sunspot derived from spectropolarimetry of Ca II 8542 A

TL;DR

This study uses spectropolarimetric data of the Ca II 8542 A line to infer the chromospheric magnetic field in a sunspot, revealing spatial variations and magnetic field components.

Contribution

It applies the center-of-gravity and weak field approximation methods to chromospheric spectropolarimetric data for magnetic field inference, which is a novel approach for this spectral line.

Findings

LOS magnetic field strength reaches up to 800 G in the umbra

Magnetic field decreases towards the sunspot edges

Horizontal and vertical magnetic components are derived

Abstract

We analyze spectropolarimetric observations of the chromospheric Ca II 8542 A line taken by the Interferometric Bidimensional Spectrometer (IBIS) at the Dunn Solar Telescope. The data were observed on 2012 January 29 for the NOAA active region 11408. Adopting the center-of-gravity (COG) approach we obtain the line-of-sight (LOS) field strength for the chromospheric IBIS data of Ca II 8542 A line. The LOS strength of the magnetic field is determined in the target active region inside a field of view 45 x 95 arcsec. The LOS field values were found to be increase up to 800 G inside the umbral region and decrease systematically toward the edges of a sunspot. Under the weak field approximation (WFA), the horizontal, vertical magnetic field components and azimuthal field vector are obtained.