On the solar nickel and oxygen abundances

TL;DR

This study refines the solar nickel abundance using advanced 3D models and assesses its impact on the derived solar oxygen abundance, suggesting a downward revision and convergence around log epsilon_O = 8.7.

Contribution

It provides a new, more accurate measurement of the solar nickel abundance using 3D hydrodynamic models, affecting the inferred solar oxygen content.

Findings

Revised solar nickel abundance: log epsilon_Ni = 6.17.

Downward revision of solar oxygen abundance to log epsilon_O ≈ 8.7.

Convergence of oxygen abundance measurements around log epsilon_O = 8.7.

Abstract

Determinations of the solar oxygen content relying on the neutral forbidden transition at 630 nm depend upon the nickel abundance, due to a Ni I blend. Here we rederive the solar nickel abundance, using the same ab initio 3D hydrodynamic model of the solar photosphere employed in the recent revision of the abundances of C, N, O and other elements. Using 17 weak, unblended lines of Ni I together with the most accurate atomic and observational data available we find log epsilon_Ni = 6.17 +/- 0.02 (statistical) +/- 0.05 (systematic), a downwards shift of 0.06 to 0.08 dex relative to previous 1D-based abundances. We investigate the implications of the new nickel abundance for studies of the solar oxygen abundance based on the [O I] 630 nm line in the quiet Sun. Furthermore, we demonstrate that the oxygen abundance implied by the recent sunspot spectropolarimetric study of Centeno & Socas-Navarro needs to be revised downwards from log epsilon_O = 8.86 +/- 0.07 to 8.71 +/- 0.10. This revision is based on the new nickel abundance, application of the best available gf-value for the 630 nm forbidden oxygen line, and a more transparent treatment of CO formation. Determinations of the solar oxygen content relying on forbidden lines now appear to converge around log epsilon_O = 8.7.