On the collisional sensitivity of polarized Mg II solar lines

TL;DR

This paper calculates collisional rates for Mg II lines with hydrogen and assesses their impact on solar polarization diagnostics, revealing sensitivity at hydrogen densities above 10^14 cm^-3.

Contribution

It provides comprehensive collisional data for Mg II with hydrogen and analyzes their effects on line polarization in solar conditions.

Findings

Polarization of some Mg II lines is sensitive to collisions at high hydrogen densities.

Collisional rates significantly influence the interpretation of Mg II spectral lines in solar diagnostics.

The study offers essential data for improving solar magnetic field measurements.

Abstract

Neutral and singly ionized states of the Magnesium (Mg) are the origin of several spectral lines that are useful for solar diagnostic purposes. An important element in modeling such solar lines is collisional data of the Mg with different perturbers abundant in the Sun, specially with neutral hydrogen. This work aims at providing complete depolarization and polarization and population transfer data for Mg II due to collisions with hydrogen atoms. For this purpose, a general formalism is employed to calculate the needed rates of MgII due to collisions with hydrogen atoms. The resulting collisional rates are then employed to investigate the impact of collisions on the polarization of 25 Mg II lines relevant to solar applications by solving the governing statistical equilibrium equations within multi-level and multi-term atomic models. We find that the polarization of some Mg II lines starts to be sensitive to collisions for hydrogen density $n_H \!\gtrsim\!$ 10$^{14}$ cm$^{-3}$.