Solar Forbidden Oxygen, Revisited

Abstract

Recent large reductions in the solar oxygen abundance, based on synthesis of photospheric O I, OH, and CO absorptions with 3D convection models, have provoked consternation in the helioseismology community: the previous excellent agreement between measured p-mode oscillation frequencies and predictions based on the recommended O of a decade ago (680 parts per million [ppm] relative to hydrogen) unravels at the new low value (460 ppm). In an attempt to reconcile these conflicting results, the formation of pivotal [O I] λ6300, which is blended with a weak Ni I line, has been reconsidered, exploiting an alternative 3D model (albeit only a single temporal snapshot). And while there are several areas of agreement with the earlier [O I] studies of Allende Prieto, Asplund, and others, there is one crucial point of disagreement: the O derived here is significantly larger, 650 ± 65 ppm (although at the expense of a ~30% weaker Ni I line than expected from the recommended nickel abundance). One innovation is a more robust treatment of the solar wavelengths: the balance between the components of the [O I] + Ni I blend is sensitive to velocity errors of only a few hundred m s−1. A second improvement is enforcement of a "continuum calibration" to ensure a self-consistent 3D temperature scale. Because of the renewed agreement between the linchpin tracer [O I] and seismic oxygen, the proposed downward slump of the solar metallicity and the perceived "oxygen crisis" now can be said to rest on less secure footings.

Keywords

Affiliated Institutions

• University of Colorado Boulder US

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