A solar photospheric “ thermal profiling ” analysis is presented , exploiting the infrared ( 2.3–4.6 µm ) 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 \equiv 0.5 ) .
Our analysis was meant to complement recent studies based on 3-D convection models which , among other things , have revised the historical solar oxygen ( and carbon ) abundance downward by a factor of nearly two ; although in fact our conclusions do not support such a revision .
Based on various considerations , an \epsilon _ { ~ { } O } = 700 { \pm } 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 : ^ { 12 } C/ ^ { 13 } C= 80 { \pm } 1 , ^ { 16 } O/ ^ { 17 } O= 1700 { \pm } 220 , and ^ { 16 } O/ ^ { 18 } O= 440 { \pm } 6 ; all significantly lower than terrestrial .
CO synthesis experiments utilizing a stripped down version of the 3-D 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 ( \sim 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 mid-photospheric convective properties .