Non-LTE effects on titanium in late-type stars

by Mr Jack Mallinson (Stockholm University)

Friday 8 Mar 2024, 10:30 → 11:30 Europe/Stockholm

FC61 (AlbaNova Main Building)

Iron peak elements are vital tracers of Galactic chemical evolution due to their formation in both Type Ia and core-collapse supernovae, and are analysed in large scale surveys such as GALAH and WEAVE. While iron is arguably the most important of them, titanium is also a powerful indicator in Galactic formation history. Its unique behaviour as both an iron peak and alpha element leads it to be one of the most useful elements in stellar spectroscopy and separating Galactic stellar populations. However, despite this interest and the multitude of its lines across all wavelengths, investigations often limit themselves to just its ionised form: Ti II. This is due to the historical inability to correctly model titanium in older, metal-poor stars because of the common assumption of local thermodynamic equilibrium (LTE) that leads to a large ionisation imbalance, |Ti I - Ti II| > 0. By investigating over 70,000 GALAH stars in non-LTE, we determine, for the first time, a large set of accurate non-LTE titanium abundances across a range of stellar parameters. This results in a departure coefficient grid to allow any survey to easily apply non-LTE corrections at little extra computational cost.

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