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

Abstract

We investigate the non-local thermodynamic equilibrium (non-LTE, hereafter NLTE) analysis for Cu i 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. 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 ≤ [Fe/H] ≤ −0.95 dex. For Cu i 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 Drawin’s theoretical approximation. To verify our adopted copper atomic model, we also derived the LTE copper abundances of Cu ii lines for the sample stars. A consistent copper abundance from the Cu i (NLTE) and Cu ii (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 ∼−2.0 dex < [Fe/H] < ∼−1.0 dex, favoring a secondary (metallicity-dependent) copper production.