The Impact of Inelastic Collisions with Hydrogen on NLTE Copper Abundances in Metal-Poor Stars

TL;DR

This study refines NLTE copper abundance measurements in metal-poor stars by incorporating quantum-mechanical collision data, leading to more accurate and consistent results, and provides insights into copper production in the early universe.

Contribution

It introduces an updated copper atomic model with quantum-mechanical collision data, improving NLTE abundance determinations and consistency between Cu I and Cu II lines in metal-poor stars.

Findings

NLTE copper abundances decrease with updated atomic data.

Consistent copper abundances from Cu I and Cu II lines confirm model reliability.

[Cu/Fe] ratios increase with metallicity between -2.0 and -1.0 dex.

Abstract

We investigate the non-local thermodynamic equilibrium (NLTE) analysis for \ion{Cu}{1} lines with the updated model atom that includes quantum-mechanical rate coefficients of Cu\,$+$\,H and Cu$^+$\,$+$\,H$^-$ inelastic collisions from the recent study of Belyaev et al. (2021). The influence of these data on NLTE abundance determinations has been performed for six metal-poor stars in a metallicity range of $-$2.59\,dex$\,\le$\,[Fe/H]\,$\le$\,$-$0.95\,dex. For \ion{Cu}{1} lines, the application of accurate atomic data leads to a decrease in the departure from LTE and lower copper abundances compared to that obtained with the Drawin's theoretical approximation. To verify our adopted copper atomic model, we also derived the LTE copper abundances of \ion{Cu}{2} lines for the sample stars. A consistent copper abundance from the \ion{Cu}{1} (NLTE) and \ion{Cu}{2} (LTE) lines has been obtained, which indicates the reliability of our copper atomic model. It is noted that the [Cu/Fe] ratios increase with increasing metallicity when $\sim$\,$-$2.0\,dex\,$<$\,[Fe/H]\,$<$\,$\sim$\,$-$1.0\,dex, favoring a secondary (metallicity-dependent) copper production.