The influence of convection on OH UV line formation in the atmosphere of the metal-poor red giant HD 122563.

International audienceWe utilized high-resolution spectra of the metal-poor red giant star HD 122563 and classical 1D hydrostatic ATLAS9 model atmosphere to derive the 1D LTE oxygen abundance from OH UV lines. The obtained average 1D LTE oxygen abundance is xtmean {ensuremath {A(O)_{1D LTE}} = 6.41 ± 0.16. We also used 3D hydrodynamical COBOLD and 1D hydrostatic LHD model atmospheres to correct the 1D LTE abundances for convection-related effects and to determine average 3D LTE abundance, xtmean {ensuremath {A(O)_{3D LTE}} = 6.23 ± 0.13. We found that while the oxygen abundances determined using 1D hydrostatic model atmospheres showed trends both with the line strength and excitation potential, these trends essentially disappeared in the 3D LTE case. The average 3D LTE oxygen abundance obtained from the OH UV lines agrees reasonably well with the oxygen abundances obtained in the earlier analyses from the OH IR lines and the 630.0 nm [O I] line, while the remaining small discrepancies may possibly be attributed to NLTE effects