On OH line formation and oxygen abundances in metal-poor stars

Abstract

Abstract. The formation of the UV OH spectral lines has been investigated for a range of stellar parameters in the light of 3D hydrodynamical model atmospheres. The low atmospheric temperatures encountered at low metallicities compared with the radiative equilibrium values enforced in classical 1D hydrostatic model atmospheres have a profound impact on the OH line strengths. As a consequence, the derived O abundances using 3D models are found to be systematically lower by more than 0. 2 dex for all investigated stellar parameters. We note, however, that the 3D case may not necessarily be as metallicity-independent. The apparent lack of laboratory or theoretical rate coefficients at the relevant temperatures for the involved molecular reactions unfortunately prevents a quantitative discussion on the possible effects of non-equilibrium chemistry.

O/Fe in metal-poor main sequence and subgiant stars

“…10. Analogous effects on the OH lines were discussed by Asplund & García Pérez (2001). For a given effective temperature, the infrared and ultraviolet OH lines are similarly sensitive to the effects of granulation (Asplund & García Pérez 2001).…”

“…Asplund et al 1999Asplund et al , 2000a has been applied to study the line formation of the [O ] and Fe  lines. The procedure is the same as that adopted for our recent investigation of the OH line formation (Asplund & García Pérez 2001): a strictly differential comparison has been performed between 1D  and 3D model atmospheres with identical stellar parameters. For details of the convection simulations the reader is referred to Asplund & García Pérez (2001).…”

“…The procedure is the same as that adopted for our recent investigation of the OH line formation (Asplund & García Pérez 2001): a strictly differential comparison has been performed between 1D  and 3D model atmospheres with identical stellar parameters. For details of the convection simulations the reader is referred to Asplund & García Pérez (2001). The models employed here have a range of metallicities ([Fe/H] = 0.0 to −2.0 and correspond to solar-like stars (T eff 5800, log g = 4.4) and turn-off stars (T eff 6200, log g = 4.0).…”

“…Furthermore, LTE is far from guaranteed for either the OH UV lines (Hinkle & Lambert 1975;Asplund & García Pérez 2001) or the O  7774 Å lines (Kiselman 2001 and references therein).…”

Three-dimensional hydrodynamical simulations of red giant stars: semi-global models for interpreting interferometric observations

“…Asplund et al 1999;Asplund & García Pérez 2001;Asplund et al 2009;Caffau et al 2010;Behara et al 2010;Sbordone et al 2010) and red giants (e.g. Collet et al 2007Collet et al , 2009Wende et al 2009;Kučinskas et al 2009).…”