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Galactic evolution of oxygen: 3D effects on near-UV OH lines

Jonay I. González Hernández
Instituto de Astrofísica de Canarias

Abstract
During the last decade, the interest in 3D hydrodynamical model atmospheres has grown among the scientific community dedicated to the analysis of stellar atmospheres, and in particular to the analysis of metal-poor stars. While 1D model atmospheres rely on the assumption of radiative equilibrium, 3D models represent the detailed interplay of hydrodynamics and radiation. A considerable effort has been made to compute such 3D models for metal-poor stars using the code CO5BOLD within the CIFIST (Cosmological Impact of the FIrst STars) team, an European Union funded research group.

Oxygen is the third most common element in the Universe. The measurement of oxygen lines in metal-poor unevolved stars, in particular near-UV OH lines, can provide invaluable information on the properties of the Early Galaxy.

Modelling of the line formation of OH lines is very important, especially in metal-poor stars, where 3D hydrodynamical models commonly predict cooler temperatures than plane-parallel hydrostatic models in the upper photosphere.

We have made use of a grid of 52 3D hydrodynamical model atmospheres for dwarf stars computed using the code CO5BOLD, extracted from the more extended CIFIST grid. We determine 3D-LTE abundance corrections in all the 52 3D models for several OH lines and FeI lines of different excitation potentials. We apply these 3D-LTE corrections to the individual O abundances, derived from OH lines, of a sample the metal-poor dwarf stars reported in Israelian et al.(1998, 2001) and Boesgaard et al.(1999), by interpolating the stellar parameters of the dwarfs in the grid of 3D-LTE corrections.

The new 3D-LTE Galactic [O/Fe] trend still keeps a similar trend as the 1D-LTE, i.e, increasing towards lower [Fe/H] values. We also applied 1D-NLTE corrections to 3D Fe I abundances and we still see an increasing [O/Fe] ratio towards lower metallicites. These results have been published in González Hernández et al.(2010).

2011 December 14, 13:30

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