STATISTICAL EQUILIBRIUM OF COPPER IN THE SOLAR ATMOSPHERE

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 Cu I and the ground state of Cu II. The 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 Cu I is the ultraviolet overionization. We find that NLTE leads to systematically depleted total absorption in the Cu I lines and, accordingly, positive abundance corrections. Inelastic collisions with neutral hydrogen atoms produce minor effects on the statistical equilibrium of Cu I in the solar atmosphere. For the solar Cu I 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 E sub(exc) [< or =, slant] 1.64 eV, give a 0.14 dex lower mean solar abundance compared to that from the six E sub(exc) > 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 Cu I is log epsilon sub([middot in circle]) (Cu) + 4.19 + or - 0.10, which is consistent within the error bars with the meteoritic value 4.25 + or - 0.05 of Lodders et al. The discrepancy between E sub(exc) = 1.39-1.64 eV and E sub(exc) > 3.7 eV lines can be removed when the calculated gf-values are adopted and a mean solar abundance of log epsilon sub([middot in circle])(Cu) = 4.24 + or - 0.08 is derived.