He I vector magnetic field maps of a sunspot and its superpenumbral fine-structure

TL;DR

This study uses advanced spectropolarimetric inversions of He I triplet observations to map the chromospheric magnetic field in a sunspot and its superpenumbral canopy, revealing the magnetic structure and its relation to intensity features.

Contribution

It provides the first detailed magnetic field maps of a sunspot's chromosphere using high-resolution He I triplet data and compares these with potential field extrapolations.

Findings

Superpenumbral magnetic field is not finely structured.

Fibrils are distinguished by thermalization, not magnetic flux concentrations.

The magnetic field shows a non-potential component that could indicate solar activity potential.

Abstract

Advanced inversions of high-resolution spectropolarimetric observations of the He I triplet at 1083 nm are used to generate unique maps of the chromospheric magnetic field vector across a sunspot and its superpenumbral canopy. The observations were acquired by the Facility Infrared Spectropolarimeter (FIRS) at the Dunn Solar Telescope (DST) on 29 January 2012. Multiple atmospheric models are employed in the inversions, as superpenumbral Stokes profiles are dominated by atomic-level polarization while sunspot profiles are Zeeman-dominated but also exhibit signatures perhaps induced by symmetry breaking effects of the radiation field incident on the chromospheric material. We derive the equilibrium magnetic structure of a sunspot in the chromosphere, and further show that the superpenumbral magnetic field does not appear finely structured, unlike the observed intensity structure. This suggests fibrils are not concentrations of magnetic flux but rather distinguished by individualized thermalization. We also directly compare our inverted values with a current-free extrapolation of the chromospheric field. With improved measurements in the future, the average shear angle between the inferred magnetic field and the potential field may offer a means to quantify the non-potentiality of the chromospheric magnetic field to study the onset of explosive solar phenomena.