3D non-LTE line formation in the solar photosphere and the solar oxygen abundance

TL;DR

This study investigates the formation of oxygen spectral lines in the solar photosphere using 3D hydrodynamic models, revealing that non-LTE effects influence abundance measurements but do not fully resolve existing discrepancies.

Contribution

It introduces a 3D non-LTE modeling approach for oxygen lines in the solar photosphere, highlighting limitations of 1D models and implications for solar oxygen abundance estimates.

Findings

3D models reduce but do not eliminate abundance discrepancies.

Non-LTE effects are significant for the 777 nm triplet.

Solar oxygen abundance may be below 8.8 in logarithmic scale.

Abstract

We study the formation of O I and OH spectral lines in three-dimensional hydrodynamic models of the solar photosphere. The line source function of the O I 777 nm triplet is allowed to depart from local thermodynamic equilibrium (LTE), within the two-level-atom approximation. Comparison with results from 1D models show that the 3D models alleviate, but do not remove, the discrepancy between the oxygen abundances reported from non-LTE work on the 777 nm triplet and from the [O I] 630 nm and OH lines. Results for the latter two could imply that the solar oxygen abundance is below 8.8 (lg(H) = 12). If this is confirmed, the discrepancy between theory and observation for the 777 nm triplet lines might fall within the range of errors in equivalent width measurements and f-values. The line source function of the 777 nm triplet in the 1.5D approximation is shown to differ insignificantly from the full 3D non-LTE result.