Computer Science – Sound
Scientific paper
Jan 2012
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21914408a&link_type=abstract
American Astronomical Society, AAS Meeting #219, #144.08
Computer Science
Sound
Scientific paper
For years, controversy has raged over what seemingly should be a well-established property of our Sun, the solar oxygen abundance. Spectroscopic estimates early last decade based on advanced 3D time-dependent photospheric convection simulations, suggested that the true oxygen abundance was almost 40% lower than the value (680 ppm relative to hydrogen) recommended only a few years prior. The unexpectedly low value sparked what has come to be called the ``Solar Oxygen Crisis,'' because the previous higher abundance was almost exactly what was required by helioseismology to reproduce the interior sound speed profile, well-characterized from surface p-mode measurements. Although in most other parts of Astronomy, agreement to within a factor of two is cause for celebration, in this case -- despite intense efforts on both sides -- there did not seem to be an easy way to reconcile the disparate results from the inside and outside of the Sun. In this study, I examine the surface spectroscopy side of the issue, bringing to bear additional diagnostics, such as center-to-limb behavior, on the one hand to validate the thermal properties of the 3D convection models, and on the other to provide additional leverage on the abundance issue. The main conclusion is that existing 3D models can reproduce the key continuum center-limb effect in the visible, showing that the mean thermal gradient in the deep atmosphere is accurate, but the same models misunderestimate intensities in the inner wings of the H and K resonance lines of ionized calcium, a signature of too-low temperatures in the middle photosphere (where key oxygen bearing CO and OH reside). Implications for a unified description of the oxygen abundance from atomic and molecular species are discussed. This work supported by NSF.
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