Line formation in solar granulation: IV. [O I], OI and OH lines and the photospheric O abundance

TL;DR

This study determines the solar photospheric oxygen abundance using multiple spectral lines and advanced 3D models, finding a lower value consistent with interstellar measurements, but raising questions about solar interior models.

Contribution

It provides a consistent 3D non-LTE analysis of various oxygen lines, leading to a revised lower solar oxygen abundance with implications for solar composition models.

Findings

Derived solar oxygen abundance of log O = 8.66 ± 0.05

Consistent oxygen abundance across different diagnostics

Revised abundances impact solar interior models and helioseismology

Abstract

The solar photospheric oxygen abundance has been determined from [OI], OI, OH vibration-rotation and OH pure rotation lines by means of a realistic time-dependent, 3D, hydrodynamical model of the solar atmosphere. In the case of the OI lines, 3D non-LTE calculations have been performed, revealing significant departures from LTE as a result of photon losses in the lines. We derive a solar oxygen abundance of log O = 8.66 +/- 0.05. All oxygen diagnostics yield highly consistent abundances, in sharp contrast with the results of classical 1D model atmospheres. This low value is in good agreement with measurements of the local interstellar medium and nearby B stars. This low abundance is also supported by the excellent correspondence between lines of very different line formation sensitivities, and between the observed and predicted line shapes and center-to-limb variations. Together with the corresponding down-ward revisions of the solar carbon, nitrogen and neon abundances, the resulting significant decrease in solar metal mass fraction to Z = 0.0126 can, however, potentially spoil the impressive agreement between predicted and observed sound speed in the solar interior determined from helioseismology.