3D non-LTE Mg abundance

However, previous studies of Mgi and Mgii lines in metal-poor benchmark stars have flagged problems with magnesium abundances inferred from one-dimensional (1D), hydrostatic models of stellar atmospheres, both with or without the local thermodynamic equilibrium (LTE) approximation.We here present 3D non-LTE calculations for magnesium in FG-type dwarfs, and provide corrections for 1D LTE abundances.

The 3D non-LTE corrections reduce the ionisation imbalances in the benchmark metal-poor stars HD84937 and HD140283 from -0.16dex and -0.27dex in 1D LTE, to just -0.02dex and -0.09dex respectively.We then applied our abundance corrections to 1D LTE literature results for stars in the thin disc, thick disc, alpha-rich halo, and alpha-poor halo. We find that the 3D non-LTE results show a richer substructure in [Mg/Fe]-[Fe/H] in the alpha-poor halo, revealing two subpopulations at the metal-rich end.