Titanium abundances in late-type stars I. 1D non-local thermodynamic equilibrium modelling in benchmark dwarfs and giants
| Autor: | Mallinson, J. W. E., Lind, K., Amarsi, A. M., Barklem, P. S., Grumer, J., Belyaev, A. K., Youakim, K. |
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| Rok vydání: | 2022 |
| Předmět: | |
| Zdroj: | A&A 668, A103 (2022) |
| Druh dokumentu: | Working Paper |
| DOI: | 10.1051/0004-6361/202244788 |
| Popis: | The titanium abundances of late-type stars are important tracers of Galactic formation history. However, abundances inferred from Ti I and Ti II lines can be in stark disagreement in very metal-poor giants. Departures from local thermodynamic equilibrium (LTE) have a large impact on the minority neutral species and thus influences the ionisation imbalance, but satisfactory non-LTE modelling for both dwarfs and giants has not been achieved in previous literature. The reliability of titanium abundances is reassessed in benchmark dwarfs and giants using a new non-LTE model and one-dimensional (1D) model atmospheres. A comprehensive model atom was compiled with a more extended level structure and newly published data for inelastic collisions between Ti I and neutral hydrogen. In 1D LTE, the Ti I and Ti II lines agree to within $0.06$ dex for the Sun, Arcturus, and the very metal-poor stars HD84937 and HD140283. For the very metal-poor giant HD122563, the Ti I lines give an abundance that is $0.47$ dex lower than that from Ti II. The 1D non-LTE corrections can reach $+0.4$ dex for individual Ti I lines and $+0.1$ dex for individual Ti II lines, and reduce the overall ionisation imbalance to $-0.17$ dex for HD122563. However, it also increases the imbalance for the very metal-poor dwarf and sub-giant to around $0.2$ dex. Using 1D non-LTE reduces the ionisation imbalance in very metal-poor giants but breaks the balance of other very metal-poor stars, consistent with the conclusions in earlier literature. To make further progress, consistent 3D non-LTE models are needed. Comment: 9 pages plus appendix, 6 figures; accepted for publication in Astronomy & Astrophysics |
| Databáze: | arXiv |
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