STATISTICAL EQUILIBRIUM OF COPPER IN THE SOLAR ATMOSPHERE

Abstract

Non-local thermodynamic equilibrium (NLTE) line formation for neutral copper in the one-dimensional solar atmospheres is presented for the atomic model, including 96 terms of Cui and the ground state of Cuii .T he accurate oscillator strengths for all the line transitions in model atom and photoionization cross sections were calculated using the R-matrix method in the Russell–Saunders coupling scheme. The main NLTE mechanism for Cui is the ultraviolet overionization. We find that NLTE leads to systematically depleted total absorption in the Cui lines and, accordingly, positive abundance corrections. Inelastic collisions with neutral hydrogen atoms produce minor effects on the statistical equilibrium of Cui in the solar atmosphere. For the solar Cui lines, the departures from LTE are found to be small, the mean NLTE abundance correction of ∼0.01 dex. It was found that the six low-excitation lines, with excitation energy of the lower level Eexc 1.64 eV, give a 0.14 dex lower mean solar abundance compared to that from the six Eexc > 3.7 eV lines, when applying experimental gf -values of Kock & Richter. Without the two strong resonance transitions, the solar mean NLTE abundance from 10 lines of Cui is log e� (Cu) = 4.19 ± 0.10, which is consistent within the error bars with the meteoritic value 4.25 ± 0.05 of Lodders et al. The discrepancy between Eexc = 1.39–1.64 eV and Eexc > 3.7 eV lines can be removed when the calculated gf -values are adopted and a mean solar abundance of log e� (Cu) = 4.24 ± 0.08 is derived.