Journal Article

Ionization balance of Ti in the photospheres of the Sun and four late-type stars

Maria Bergemann

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 413, issue 3, pages 2184-2198
Published in print May 2011 | ISSN: 0035-8711
Published online May 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.18295.x
Ionization balance of Ti in the photospheres of the Sun and four late-type stars

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In this paper we investigate statistical equilibrium of Ti in the atmospheres of late-type stars. The Ti i/Ti ii level populations are computed with available experimental atomic data, except for photoionization and collision-induced transition rates, for which we have to rely on theoretical approximations. For the Sun, the non-local thermodynamic equilibrium (NLTE) line formation with adjusted H i inelastic collision rates and mafags-os model atmosphere solve the long-standing discrepancy between Ti i and Ti ii lines. The NLTE abundances determined from both ionization stages agree within 0.01 dex with each other and with the Ti abundance in C i meteorites. The Ti NLTE model does not perform similarly well for the metal-poor stars, overestimating NLTE effects in the atmospheres of dwarfs, but underestimating overionization for giants. Investigating different sources of errors, we find that only [Ti/Fe] ratios based on Ti ii and Fe ii lines can be safely used in studies of Galactic chemical evolution. To avoid spurious abundance trends with metallicity and dwarf/giant discrepancies, it is strongly recommended to disregard Ti i lines in abundance analyses, as well as in determination of surface gravities.

Keywords: line: formation; line: profiles; radiative transfer; Sun: abundances; stars: abundances

Journal Article.  10995 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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