RSAA Colloquia / Seminars / Feast-of-Facts: Tuesday, 23 August 2016, 11:00-12:00; Duffield Lecture Theatre

Anish Amarsi

"Three dimensional non-local thermodynamic equilibrium (3D non-LTE) spectral line formation in late-type stars"

As part of my PhD thesis I have performed some of the first ever non-LTE spectral line formation calculations, highlighting serious systematic errors in traditional 1D LTE analyses. In this talk I present results for two of the most important metals in astronomy: oxygen and iron. For the OI 777nm triplet, we found severe 3D non-LTE effects in solar-metallicity turn-off stars, where the abundance corrections can reach around -0.7 dex. In disagreement with several previous studies based on 1D non-LTE calculations, we found the effects become monotonically smaller towards lower metallicities. For FeI and FeII lines, we found the 3D non-LTE effects to grow towards lower metallicities, which has a large impact on the FeI excitation balance and FeI/FeII ionization balance in metal-poor stars. I discuss the implications of these results on spectroscopic stellar parameter determinations and on the [O/Fe] vs [Fe/H] relationship, one of the key tracers of the Galactic Chemical Evolution.