Depths of formation of magnetically sensitive absorption lines

TL;DR

This paper investigates how magnetic fields influence the formation depths of absorption lines in the solar atmosphere, revealing that magnetic strength affects line formation height and polarization profiles.

Contribution

It introduces a detailed analysis of depression contribution functions for magnetically sensitive lines, showing their dependence on magnetic field strength and line asymmetry.

Findings

Steep line profile sections form higher in strong magnetic fields.

Polarization profiles form several kilometers above unpolarized lines.

Average line formation depth is nearly independent of magnetic field strength.

Abstract

Characteristics of the depression contribution functions are studied for the Stokes line profiles formed in a magnetic field. The form of the depression functions depends mainly on the strength of splitting and the Zeeman component intensity, and is of a complicated character with a distinctly pronounces asymmetry. The depths of formation of magnetically sensitive lines are found by means of these contribution functions. The calculations reveal that the steep section of the line profile is formed higher than the profile center when a strong longitudinal magnetic field is present. The Stokes profiles that describe the polarization characteristics are formed only several kilometers higher than the Stokes profile that specifies the general depression of the unpolarized and polarized radiation. The averaged depth of formation of the whole line profile is practically independent of the magnetic field strength. The depths of formation of 17 photospheric lines usually used in magnetospectroscopic observations are calculated for the models of the quiet photosphere, a flux tube, and the sunspot umbra.