Non-LTE abundances of zinc in different spectral type stars and the Galactic [Zn/Fe] trend based on quantum-mechanical data on inelastic processes in zinc-hydrogen collisions

TL;DR

This study develops a new non-LTE model for zinc in stars, using quantum-mechanical data, and analyzes zinc abundances across different stellar types and metallicities, revealing trends in the Galactic [Zn/Fe] ratio.

Contribution

It introduces the first non-LTE analysis of Zn I and Zn II lines in UV spectra of metal-poor stars using updated quantum-mechanical collision data.

Findings

Non-LTE corrections increase Zn I abundance by 0.17 dex.

[Zn/Fe] shows a dip at intermediate metallicities.

First non-LTE zinc abundances for seven B to F-type stars.

Abstract

We present a new model atom of Zn I-II based on the most up-to-date photoionisation cross-sections, electron-impact excitation rates, and rate coefficients for the Zn I + H I and Zn II + H- collisions. The latter were calculated using the multi-channel quantum asymptotic treatment based on the Born-Oppenheimer approach. Non-LTE analysis was performed for the first time for lines of Zn I and Zn II in the ultraviolet (UV) spectra of two very metal-poor reference stars, HD 84937 and HD 140283. We found consistent non-LTE abundance from the resonance Zn I 2138 A line, the subordinate lines, and the lines of Zn II. In both stars, non-LTE leads to 0.17 dex higher average abundance from Zn I, while, for Zn II lines, non-LTE corrections are minor and do not exceed 0.06 dex. Using lines of Zn I in the high-resolution spectra, we determined the non-LTE abundances for a sample of 80 stars in the -2.5 < [Fe/H] < 0.2 metallicity range. The [Zn/Fe] versus [Fe/H] diagram reveals a dip, with [Zn/Fe] = 0.3 in the most metal-poor stars, a close-to-solar value for [Fe/H] = -1.2, and increasing [Zn/Fe] up to 0.3 in the thick disk stars. The close-to-solar metallicity stars have subsolar [Zn/H] = -0.1, on average. Non-LTE abundances of zinc were derived for the first time for seven reference F to B-type stars. We provide a grid of the non-LTE abundance corrections.