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Fe I/Fe II ionization equilibrium in cool stars: NLTE versus LTE

Published online by Cambridge University Press:  09 March 2010

Lyudmila Mashonkina ,
Thomas Gehren ,
Jianrong Shi ,
Andreas Korn  and
Frank Grupp
Lyudmila Mashonkina
Affiliation:
Institute of Astronomy, Russian Academy of Science, Pyatnitskaya 48, 119017 Moscow, Russia email: lima@inasan.ru Universitäts-Sternwarte München, Scheinerstr. 1, 81679 München, Germany email: lyuda@usm.lmu.de, gehren@usm.lmu.de, fug@usm.lmu.de
Thomas Gehren
Affiliation:
Universitäts-Sternwarte München, Scheinerstr. 1, 81679 München, Germany email: lyuda@usm.lmu.de, gehren@usm.lmu.de, fug@usm.lmu.de
Jianrong Shi
Affiliation:
National Astronomical Observatories, Chinese Academy of Sciences, A20 Datun Road, Chaoyang District, Beijing 100012, PR China email: sjr@bao.ac.cn
Andreas Korn
Affiliation:
Department of Physics and Astronomy, Uppsala University, Box 515, 75120 Uppsala, Sweden email: andreas.korn@fysast.uu.se
Frank Grupp
Affiliation:
Universitäts-Sternwarte München, Scheinerstr. 1, 81679 München, Germany email: lyuda@usm.lmu.de, gehren@usm.lmu.de, fug@usm.lmu.de
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Abstract

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Non-local thermodynamic equilibrium (NLTE) line formation for neutral and singly-ionized iron is considered through a range of stellar parameters characteristic of cool stars. A comprehensive model atom for Fe I and Fe II is presented. Our NLTE calculations support the earlier conclusions that the statistical equilibrium (SE) of Fe I shows an underpopulation of Fe I terms. However, the inclusion of the predicted high-excitation levels of Fe I in our model atom leads to a substantial decrease in the departures from LTE. As a test and first application of the Fe I/II model atom, iron abundances are determined for the Sun and four selected stars with well determined stellar parameters and high-quality observed spectra. Within the error bars, lines of Fe I and Fe II give consistent abundances for the Sun and two metal-poor stars when inelastic collisions with hydrogen atoms are taken into account in the SE calculations. For the close-to-solar metallicity stars Procyon and β Vir, the difference (Fe II - Fe I) is about 0.1 dex independent of the line formation model, either NLTE or LTE. We evaluate the influence of departures from LTE on Fe abundance and surface gravity determination for cool stars.

Keywords

atomic dataline: formationstars: atmospheres
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 5 , Symposium S265: Chemical Abundances in the Universe: Connecting First Stars to Planets , August 2009 , pp. 197 - 200
Copyright
Copyright © International Astronomical Union 2010

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