We consider the formation of solar infrared ( 2–6 \mu m ) rovibrational bands of carbon monoxide ( CO ) in CO5BOLD 3D convection models , with the aim to refine abundances of the heavy isotopes of carbon ( ^ { 13 } C ) and oxygen ( ^ { 18 } O , ^ { 17 } O ) , to compare with direct capture measurements of solar wind light ions by the Genesis Discovery Mission .
We find that previous , mainly 1D , analyses were systematically biased toward lower isotopic ratios ( e.g. , R _ { 23 } \equiv ^ { 12 } C/ ^ { 13 } C ) , suggesting an isotopically “ heavy ” Sun contrary to accepted fractionation processes thought to have operated in the primitive solar nebula .
The new 3D ratios for ^ { 13 } C and ^ { 18 } O are : R _ { 23 } = 91.4 { \pm } 1.3 ( R _ { \oplus } = 89.2 ) ; and R _ { 68 } = 511 { \pm } 10 ( R _ { \oplus } = 499 ) , where the uncertainties are 1 \sigma and “ optimistic. ” We also obtained R _ { 67 } = 2738 { \pm } 118 ( R _ { \oplus } = 2632 ) , but we caution that the observed ^ { 12 } C ^ { 17 } O features are extremely weak .
The new solar ratios for the oxygen isotopes fall between the terrestrial values and those reported by Genesis ( R _ { 68 } = 530 , R _ { 67 } = 2798 ) , although including both within 2 \sigma error flags , and go in the direction favoring recent theories for the oxygen isotope composition of Ca–Al inclusions ( CAI ) in primitive meteorites .
While not a major focus of this work , we derive an oxygen abundance , \epsilon _ { O } \sim 603 { \pm } 9 ppm ( relative to hydrogen ; \log { \epsilon } \sim 8.78 on the { H } = 12 scale ) .
That the Sun likely is lighter than the Earth , isotopically speaking , removes the necessity to invoke exotic fractionation processes during the early construction of the inner solar system .