The impact of non-LTE effects and granulation inhomogeneities on the derived iron and oxygen abundances in metal-poor halo stars

This paper presents the results of a detailed theoretical investigation of the impact of non-LTE effects and of granulation inhomogeneities on the derived iron and oxygen abundances in the metal-poor halo subgiant HD140283. Our analysis is based on both the ‘classical’ one-dimensional (1D) stellar atmosphere models and on the new generation of three-dimensional (3D) hydrodynamical models. The non-LTE calculations presented here have been carried out without inelastic collisions with neutral hydrogen atoms. We find that if non-LTE effects are taken into account when synthetizing the Fe i spectrum in both type of models, then the derived iron abundance turns out to be very similar in both cases. The emergent spectral line profiles in both models are very much weaker in non-LTE than in LTE because the UV overionization mechanism produces a very strong Consejo Superior de Investigaciones Cient́ıficas; Spain