Collisional effects on the formation of the second solar spectrum of the Sr {\sc ii} $\lambda$4078 line

TL;DR

This study investigates how isotropic collisions with hydrogen atoms influence the polarization of the Sr II λ4078 line in the solar spectrum, highlighting the importance of including metastable levels in models for accurate predictions.

Contribution

It demonstrates that considering isotropic collisions and the metastable level 4d of Sr II is crucial for accurate modeling of the line's polarization.

Findings

Isotropic collisions significantly affect polarization in certain hydrogen density ranges.

Neglecting the metastable level 4d can cause up to 25% errors in polarization estimates.

Proper atomic modeling improves understanding of the second solar spectrum.

Abstract

This work aims to provide key elements to gain better understanding of the formation of the second solar spectrum of the Sr II $\lambda$4078 line. We show that in a certain range of hydrogen density, the effect of isotropic collisions between Sr II ions with hydrogen atoms is important in determining the polarization of the Sr II $\lambda$4078 line. The use of an atomic model that neglects the metastable level 4d of Sr II can induce errors of up to 25 \% in the value of the scattering polarization of the solar Sr II $\lambda$4078 line.