PI: Kenneth Hinkle, NOAO, email@example.com
Address: NGSC, P.O. Box 26732, Tucson, AZ 85726, USA
CoI: David Lambert, University of Texas
CoI: Verne Smith, NOAO
CoI: Thomas Lebzelter, University of Vienna
Title: The HdC stars as recently merged white dwarf binaries
Abstract: The hydrogen-deficient carbon star HD 137613 has been reported by Clayton et al. (2005) to have the extraordinary isotopic ratio ^16O/^18O ~ 0.8. The solar system ratio is ~500 and carbon stars typically have yet larger ratios. The explanation proposed for the ^16O/^18O value observed in HD 137613 is that the HdC stars are recently merged white dwarf binaries. The observed supergiant HdC star is a transient post-merger phase. If so, we have the rare opportunity to see helium-burning shell products in a low gravity stellar environment. To test this model we propose to measure the CNO elemental abundances for HD 137613 as well as the other four hydrogen- deficient carbon stars. Comparison of the measure abundances with models will lead to considerable insight into stellar mergers and nucleosynthesis.
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