Non-LTE iron abundances in cool stars: The role of hydrogen collisions

TL;DR

This paper develops an empirical method to calibrate hydrogen collision cross-sections for iron in stellar atmospheres, improving non-LTE abundance determinations in cool stars.

Contribution

It introduces a new iron model atom incorporating hydrogen collisions for excitation, ionization, and charge transfer, which had not been quantum mechanically calculated before.

Findings

Hydrogen charge transfer collisions significantly affect non-LTE modeling.

The new model improves iron abundance accuracy in benchmark stars.

Application to the Sun, α Cen A, and HD140283 demonstrates the model's effectiveness.

Abstract

In the aim of determining accurate iron abundances in stars, this work is meant to empirically calibrate H-collision cross-sections with iron, where no quantum mechanical calculations have been published yet. Thus, a new iron model atom has been developed, which includes hydrogen collisions for excitation, ionization and charge transfer processes. We show that collisions with hydrogen leading to charge transfer are important for an accurate non-LTE modeling. We apply our calculations on several benchmark stars including the Sun, the metal-rich star {\alpha} Cen A and the metal-poor star HD140283.