Non-LTE analysis of the formation of EuII lines in the atmospheres of solar-type stars

A method to analyze the statistical equilibrium of the EuII ion based on a 36-level model atom has been developed. The formation of EuII lines without assuming local thermodynamic equilibrium (LTE) is considered for T-eff = 5 500-7000 K, log g = 4.0, and metallicities [A] from 0 to -1.5. Non-LTE effe cts in the level populations are primarily due to radiative pumping of exci ted states from the ground and low-lying levels, which leads to over-popula tion of upper relative to lower levels. As a result, the studied lambda 412 9 and lambda 6645 Angstrom lines are weaker than in the LTE case. However, due to the small energy differences between even low-lying EuII levels, col lisional coupling is strong, and deviations from LTE in EuII lines are mode st: for the Sun, non-LTE corrections to the abundance are only 0.04 dex. Th e non-LTE effects grow with an increase in the effective temperature and wi th a decrease in the metallicity, so that non-LTE abundance corrections can reach 0.12 dex for T-eff = 5500K, log g = 4.0, [A] = -1.5 and 0.1 dex for T-eff = 7000K, log g = 4.0, [A] = 0. The effect of inaccuracy in the atomic parameters for EuII on the non-LTE calculations is examined. Analysis of t he profiles of the solar EuII lambda 4129 and lambda 6645 Angstrom, lines i s used to empirically refine estimates of the efficiency of collisional pro cesses in forbidden transitions in establishing the distribution of EuII io ns over excited states. (C) 2000 MAIK "Nauka/Interperiodica".