Solar carbon monoxide, thermal profiling, and the abundances of C, O, and their isotopes

A solar photospheric "thermal profiling'' analysis is presented, exploiting the infrared (2.3-4.6 mu m) rovibrational bands of carbon monoxide (CO) as observed with the McMath-Pierce Fourier transform spectrometer (FTS) at Kitt Peak, and from above the Earth's atmosphere by the Shuttle-borne ATMOS experiment. Visible continuum intensities and center-limb behavior constrained the temperature profile of the deep photosphere, while CO center-limb behavior defined the thermal structure at higher altitudes. The oxygen abundance was self-consistently determined from weak CO absorptions (for C/O equivalent to 0: 5). Our analysis was meant to complement recent studies based on three-dimensional (3D) convection models, which, among other things, have revised the historical solar oxygen (and carbon) abundance downward by a factor of nearly 2, although in fact our conclusions do not support such a revision. Based on various considerations, an epsilon(O) = 700 +/- 100 ppm (parts per million relative to hydrogen) is recommended; the large uncertainty reflects the model sensitivity of CO. New solar isotopic ratios also are reported: C-12/C-13 80 +/- 1, O-16/O-17 = 1700 +/- 220, and O-16/O-18 440 +/- 6-all significantly lower than terrestrial. CO synthesis experiments utilizing a stripped down version of the 3D model-which has large temperature fluctuations in the middle photosphere, possibly inconsistent with CO "movies'' from the Infrared Imaging Spectrometer (IRIS), and a steeper mean temperature gradient than matches visible continuum center-limb measurements-point to a lower oxygen abundance (similar to 500 ppm) and isotopic ratios closer to terrestrial. A low oxygen abundance from CO-and other molecules like OH-thus hinges on the reality of the theoretically predicted midphotospheric convective properties.