Is the sun lighter than the earth? Isotopic co in the photosphere, viewed through the lens of three-dimensional spectrum synthesis

Thomas R. Ayres, J. R. Lyons, H. G. Ludwig, E. Caffau, S. Wedemeyer-Böhm

Research output: Contribution to journalArticle

17 Scopus citations

Abstract

We consider the formation of solar infrared (2-6 μm) rovibrational bands of carbon monoxide (CO) in CO5BOLD 3D convection models, with the aim of refining abundances of the heavy isotopes of carbon (13C) and oxygen (18O, 17O), 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 2312C/13C), suggesting an isotopically "heavy" Sun contrary to accepted fractionation processes that were thought to have operated in the primitive solar nebula. The new 3D ratios for 13C and 18O are R 23 = 91.4 ± 1.3 (R = 89.2) and R 68 = 511 ± 10 (R = 499), where the uncertainties are 1σ and "optimistic." We also obtained R 67 = 2738 ± 118 (R = 2632), but we caution that the observed 12C 17O 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 2σ error flags, and go in the direction favoring recent theories for the oxygen isotope composition of Ca-Al inclusions in primitive meteorites. While not a major focus of this work, we derive an oxygen abundance, εO ∼ 603 ± 9 ppm (relative to hydrogen; log ε ∼ 8.78 on the H = 12 scale). The fact that the Sun is likely lighter than the Earth, isotopically speaking, removes the necessity of invoking exotic fractionation processes during the early construction of the inner solar system.

Original languageEnglish (US)
Article number46
JournalAstrophysical Journal
Volume765
Issue number1
DOIs
StatePublished - Mar 1 2013
Externally publishedYes

Keywords

  • Sun: abundances
  • Sun: infrared
  • Sun: photosphere
  • line: formation
  • molecular processes

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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