Non-LTE Analysis of the Formation of EuII Lines in the Atmospheres of Solar-type Stars

Details Non-LTE Analysis of the Formation of EuII Lines in the Atmospheres of Solar-type Stars Non-LTE Analysis of the Formation of EuII Lines in the Atmospheres of Solar-type Stars

Aug 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000arep...44..558m&link_type=abstract

Astronomy Reports, Volume 44, Issue 8, August 2000, pp.558-568

Astronomy and Astrophysics

Astronomy

7

Scientific paper

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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