Thomas R. Ayres (Center for Astrophysics and Space Astronomy of the University of Colorado, Boulder, U.S.A.)

C/O isotopes in the Sun & the solar oxygen abundance
When Oct 12, 2012 from 10:30 AM to 12:00 PM
What
  • Special Seminar
Where SH, Lecture hall
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Recent results from NASA's Genesis Discovery Mission, whose objective was to directly capture CNO ions from the solar wind, suggest that the Sun is isotopically `lighter' than the Earth.  This is in line with theoretical understanding of fractionation processes in the primitive solar nebula, but contrary to a series of solar photospheric measurements -- based mainly on isotopic variants of the CO molecule, notably an early study by  Hall, Noyes, & Ayres (1972) -- that suggested that the Sun might be as `heavy' or heavier than the Earth. Now, 40 years later, a whole new series of tools have been brought to the problem, including (most importantly) ab initio solar 3D convection models, as well as broad band measurements of the infrared CO bands (2-6 microns) from the highly precise ATMOS FTS spectrometer in orbit (on Space Shuttle, in the 1990's).  I show how the new CO spectra and new  3D models join to trim some isotopic weight off the Sun, and tip the spectroscopic view toward that of Genesis, although not completely the whole way.  The story is a cautionary tale concerning the limitations of historical 1D spectrum synthesis, which produces especially bad results for the particular case of the molecules with their ultra-sensitivity to atmospheric thermal properties; but also a glimpse of what can be accomplished with high-precision "forensic" spectroscopy of the solar plasma.