Spectropolarimetric capabilities of Ca II 8542 A line

TL;DR

This paper evaluates the diagnostic capabilities of the Ca II 8542 Å line for studying the solar chromosphere's magnetic fields, using response functions and 3D MHD simulations to assess its sensitivity and polarization signals.

Contribution

It provides a detailed analysis of the Ca II 8542 Å line's sensitivity to physical parameters and magnetic fields, aiding future observational studies of the solar chromosphere.

Findings

The line is sensitive to layers between log τ=[0,-5.5].

Simulated signals reveal the 3D magnetic field geometry.

The line can infer magnetic field structures in the chromosphere.

Abstract

The next generation of space and ground-based solar missions aim to study the magnetic properties of the solar chromosphere using the infrared Ca II lines and the He I 10830 {\AA} line. The former seem to be the best candidates to study the stratification of magnetic fields in the solar chromosphere and their relation to the other thermodynamical properties underlying the chromospheric plasma. The purpose of this work is to provide a detailed analysis of the diagnostic capabilities of the Ca II 8542 {\AA} line, anticipating forthcoming observational facilities. We study the sensitivity of the Ca II 8542 {\AA} line to perturbations applied to the physical parameters of reference semi-empirical 1D model atmospheres using response functions and we make use of 3D MHD simulations to examine the expected polarization signals for moderate magnetic field strengths. Our results indicate that the Ca II 8542 {\AA} line is mostly sensitive to the layers enclosed between $\log$ $\tau=[0,-5.5]$, under the physical conditions that are present in our model atmospheres. In addition, the simulated magnetic flux tube generates strong longitudinal signals in its centre and moderate transversal signals, due to the vertical expansion of magnetic field lines, in its edge. Thus, observing the Ca II 8542 {\AA} line we will be able to infer the 3D geometry of moderate magnetic field regions.