Solar carbon monoxide: Poster child for 3D effects

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

Research output: Contribution to journalConference articlepeer-review

1 Scopus citations


Photospheric infrared (2-6 μm) rovibrational bands of carbon monoxide (CO) provide a tough test for 3D convection models such as those calculated using CO5BOLD. The molecular formation is highly temperature-sensitive, and thus responds in an exaggerated way to thermal fluctuations in the dynamic atmosphere. CO, itself, is an important tracer of the oxygen abundance, a still controversial issue in solar physics; as well as the heavy isotopes of carbon (13C) and oxygen (18O, 17O), which, relative to terrestrial values, are fingerprints of fractionation processes that operated in the primitive solar nebula. We show how 3D models impact the CO line formation, and add in a second constraint involving the near-UV Ca II line wings, which also are highly temperature sensitive, but in the opposite sense to the molecules. We find that our reference CO5BOLD snapshots appear to be slightly too cool on average in the outer layers of the photosphere where the CO absorptions and Ca II wing emissions arise. We show, further, that previous 1D modeling was systematically biased toward higher oxygen abundances and lower isotopic ratios (e.g., R2312C/13C), suggesting an isotopically "heavy" Sun contrary to direct capture measurements of solar wind light ions by the Genesis Discovery Mission. New 3D ratios for the oxygen isotopes are much closer to those reported by Genesis, and the associated oxygen abundance from CO now is consistent with the recent Caffau et al. study of atomic oxygen. Some lingering discrepancies perhaps can be explained by magnetic bright points. Solar CO demonstrates graphically the wide gulf that can occur between a 3D analysis and 1D.

Original languageEnglish (US)
Pages (from-to)85-95
Number of pages11
JournalMemorie della Societa Astronomica Italiana - Journal of the Italian Astronomical Society
StatePublished - 2013
Externally publishedYes
Event3rd Workshop on COnservative COde for the COmputation of COmpressible COnvection in a BOx of L Dimensions, CO5BOLD 2012 - Heidelberg, Germany
Duration: Oct 1 2012Oct 3 2012


  • Line: formation
  • Molecular processes
  • Sun: abundances
  • Sun: infrared
  • Sun: photosphere

ASJC Scopus subject areas

  • Electrical and Electronic Engineering
  • Radiology Nuclear Medicine and imaging
  • Astronomy and Astrophysics
  • Instrumentation
  • Atomic and Molecular Physics, and Optics


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