Abstract
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=5500–7000 K, logg=4.0, and metallicities [A] from 0 to −1.5. Non-LTE effects in the level populations are primarily due to radiative pumping of excited states from the ground and low-lying levels, which leads to over-population of upper relative to lower levels. As a result, the studied λ4129 and λ6645 Å lines are weaker than in the LTE case. However, due to the small energy differences between even low-lying EuII levels, collisional coupling is strong, and deviations from LTE in EuII lines are modest: for the Sun, non-LTE corrections to the abundance are only 0.04 dex. The non-LTE effects grow with an increase in the effective temperature and with a decrease in the metallicity, so that non-LTE abundance corrections can reach 0.12 dex for T eff=5500K, logg=4.0, [A]=−1.5 and 0.1 dex for T eff=7000K, logg=4.0, [A]=0. The effect of inaccuracy in the atomic parameters for EuII on the non-LTE calculations is examined. Analysis of the profiles of the solar EuII λ4129 and λ6645 Å lines is used to empirically refine estimates of the efficiency of collisional processes in forbidden transitions in establishing the distribution of EuII ions over excited states.
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Translated from Astronomicheski\(\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\smile}$}}{l} \) Zhurnal, Vol. 77, No. 8, 2000, pp. 630–640.
Original Russian Text Copyright © 2000 by Mashonkina.
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Mashonkina, L.I. Non-LTE analysis of the formation of EuII lines in the atmospheres of solar-type stars. Astron. Rep. 44, 558–568 (2000). https://doi.org/10.1134/1.1306356
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DOI: https://doi.org/10.1134/1.1306356