The [ITAL]Forbidden[/ITAL] Abundance of Oxygen in the Sun

TLDR

The solar photospheric 6300 Å line, attributed to forbidden neutral oxygen, is widely used to determine oxygen abundances in late‑type stars. We analyze this line with a three‑dimensional, time‑dependent hydrodynamical solar atmosphere model that reproduces observed granulation and absorption lines. Our analysis shows the line is blended with Ni I, and using accurate atomic data we derive a solar oxygen abundance of log O = 8.69 ± 0.05 dex, at the lower end of previous estimates but consistent with local interstellar medium values, highlighting the impact of the Ni I blend on stellar oxygen determinations.

Abstract

We reexamine closely the solar photospheric line at 6300 Å, which is attributed to a forbidden line of neutral oxygen and is widely used in analyses of other late-type stars. We use a three-dimensional time-dependent hydrodynamical model solar atmosphere that has been tested successfully against observed granulation patterns and an array of absorption lines. We show that the solar line is a blend with a Ni I line, as previously suggested but oftentimes neglected. Thanks to accurate atomic data on the [O I] and Ni I lines, we are able to derive an accurate oxygen abundance for the Sun: log (O) = 8.69 ± 0.05 dex, a value at the lower end of the distribution of previously published abundances but in good agreement with estimates for the local interstellar medium and hot stars in the solar neighborhood. We conclude by discussing the implication of the Ni I blend on oxygen abundances derived from [O I] λ6300 in disk and halo stars.