English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The solar photospheric abundance of oxygen is still a matter of debate. Forabout ten years some determinations have favoured a low oxygen abundance whichis at variance with the value inferred by helioseismology. Among the oxygenabundance indicators, the forbidden line at 630nm has often been considered themost reliable even though it is blended with a NiI line. In Papers I and PaperII of this series we reported a discrepancy in the oxygen abundance derivedfrom the 630nm and the subordinate [OI] line at 636nm in dwarf stars, includingthe Sun. Here we analyse several, in part new, solar observations of the thecentre-to-limb variation of the spectral region including the blend at 630nm inorder to separate the individual contributions of oxygen and nickel. We analyseintensity spectra observed at different limb angles in comparison with lineformation computations performed on a CO5BOLD 3D hydrodynamical simulation ofthe solar atmosphere. The oxygen abundances obtained from the forbidden line atdifferent limb angles are inconsistent if the commonly adopted nickel abundanceof 6.25 is assumed in our local thermodynamic equilibrium computations. With aslightly lower nickel abundance, A(Ni)~6.1, we obtain consistent fitsindicating an oxygen abundance of A(O)=8.73+/-0.05. At this value thediscrepancy with the subordinate oxygen line remains. The derived value of theoxygen abundance supports the notion of a rather low oxygen abundance in thesolar hotosphere. However, it is disconcerting that the forbidden oxygen linesat 630 and 636nm give noticeably different results, and that the nickelabundance derived here from the 630nm blend is lower than expected from othernickel lines.

The photospheric solar oxygen project: III. Investigation of the centre-to-limb variation of the 630nm [OI]-NiI blend