The Galactic chemical evolution of oxygen inferred from 3D non-LTE spectral line formation calculations

Abstract

We revisit the Galactic chemical evolution of oxygen, addressing the systematic errors inherent in classical determinations of the oxygen abundance that arise from the use of one dimensional hydrostatic (1D) model atmospheres and from the assumption of local thermodynamic equilibrium (LTE). We perform detailed 3D non-LTE radiative transfer calculations for atomic oxygen lines across a grid of 3D hydrodynamic stag- ger model atmospheres for dwarfs and subgiants. We apply our grid of predicted line strengths of the [OI] 630 nm and OI 777 nm lines using accurate stellar parameters from the literature. We infer a steep decay in [O/Fe] for [Fe/H] $\gtrsim$ -1.0, a plateau [O/Fe] $\approx$ 0.5 down to [Fe/H] $\approx$ -2.5 and an increasing trend for [Fe/H] $\lesssim$ -2.5. Our 3D non-LTE calculations yield overall concordant results from the two oxygen abundance diagnostics.