The Solar Oxygen Abundance, and the Rare Isotopes of C and O, Derived from Infrared Spectra of Carbon Monoxide


A detailed abundance analysis is presented for solar oxygen based on the ensuremathΔV=1 fundamental (4.6åisebox-0.5ex~ensuremathμm) and ensuremathΔV=2 (2.3i̊sebox-0.5ex~ensuremathμm) first- overtone rovibrational bands of carbon monoxide observed above the Earth’s atmosphere at very high spectral resolution and high signal-to-noise by the Shuttle-borne ATMOS Fourier transform spectrometer (FTS). Additional observations to define the reference photospheric thermal structure were taken of the CO fundamental bands in an atmospheric window at 2145rs̊ebox-0.5ex~cm-1 (4.6rae̊box-0.5ex~ensuremathμm) using the 1raib̊ox-0.5ex~m FTS of the McMath-Pierce telescope at Kitt Peak and a fast tip/tilt image stabilization system. The latter allowed measurements at the extreme limb where the highly slanted rays probe into the outer layers of the photosphere. High spatial resolution ``movies’’ of weak CO lines at disk center taken under excellent seeing conditions with the Infrared Imaging Spectrometer (IRIS), also on the McMath-Pierce telescope, further constrained thermal and velocity fluctuations in the layers in which the abundance-sensitive CO lines form. This work is meant to complement a series of recent studies which have revised the previously recommended solar oxygen abundance downward by nearly a factor of two; although in fact our conclusions do not support such a revision. The oxygen abundance recovered in the present work is 700ensuremath±70raiso̊x-0.5ex~ppm (parts per million relative to hydrogen) compared with the proposed downward revision to 460ensuremath±60raisex̊-0.5ex~ppm, and the recommended value of 650ensuremath±100raiseb̊-0.5ex~ppm of a decade ago. In our analysis, a fixed C/O ratio of 0.5, derived in independent work, was assumed; so the associated carbon abundance is 350raisebo-̊0.5ex~ppm. New accurate values for the solar abundance ratios of the rare isotopes of C and O also are reported: 12C/13C= 70, 16O/17O= 400, and 16O/18O= 2000. All three ratios are lower than terrestrial or meteoritic values (indicating higher isotopic abundances). We find no evidence in the ATMOS3 spectra for measurable 14C16O lines.

AGU Spring Meeting Abstracts