Non-LTE Calculations of the Mg I 12.32 $\mu$m Line in a Flaring Atmosphere

TL;DR

This paper models the behavior of the Mg I 12.32 μm line during solar flares, revealing complex changes in intensity, formation height, and polarization that impact magnetic field measurements.

Contribution

It provides the first non-LTE calculations of the Mg I 12.32 μm line response during flares, highlighting effects on line profiles and magnetic diagnostics.

Findings

Line intensity dims initially then increases during flare

Line formation height and width increase with flare heating

Flare heating affects Zeeman splitting and Stokes V profiles

Abstract

The infrared Mg I lines near 12 microns are a pair of emission lines which are magnetically sensitive and have been used to measure solar magnetic fields. Here we calculate the response of the Mg I 12.32 $\mu$m line during a flare and find that in our modeling this line has a complicated behavior. At the beginning of the flare heating, this line shows an intensity dimming at the line center. The intensity then increases when heating continues, with increasing contributions from the heated layers in the chromosphere. The line formation height and the line width also increase as a result. As for the polarized line profiles, we find that flare heating tends to decrease the Zeeman splitting width and attenuates the Stokes $V$ lobe intensity. The wider features in the Stokes $V$ profiles are more pronounced during flare heating, which should be considered when performing magnetic field inversions.