Chromospheric polarimetry through multi-line observations of the 850 nm spectral region

TL;DR

This study explores multi-line spectropolarimetric observations around 850 nm, demonstrating that nearby spectral lines enhance sensitivity to solar atmospheric parameters, improving chromospheric magnetic field measurements.

Contribution

It introduces the use of additional spectral lines near Ca II 8542 A to improve chromospheric and photospheric sensitivity in solar polarimetry.

Findings

Nearby spectral lines increase sensitivity to atmospheric parameters.

Photospheric lines improve magnetic field vector detection.

Chromospheric lines enhance atmospheric parameter sensitivity.

Abstract

Future solar missions and ground-based telescopes aim to understand the magnetism of the solar chromosphere. We performed a supporting study in Quintero Noda et al. (2016) focused on the infrared Ca II 8542 A line and we concluded that is one of the best candidates because it is sensitive to a large range of atmospheric heights, from the photosphere to the middle chromosphere. However, we believe that it is worth to try improving the results produced by this line observing additional spectral lines. In that regard, we examined the neighbour solar spectrum looking for spectral lines that could increase the sensitivity to the atmospheric parameters. Interestingly, we discovered several photospheric lines that greatly improve the photospheric sensitivity to the magnetic field vector. Moreover, they are located close to a second chromospheric line that also belongs to the Ca II infrared triplet, i.e. the Ca II 8498 A line, and enhances the sensitivity to the atmospheric parameters at chromospheric layers. We conclude that the lines in the vicinity of the Ca II 8542 A line not only increase its sensitivity to the atmospheric parameters at all layers, but also they constitute an excellent spectral window for chromospheric polarimetry.