Evidence that R Coronae Borealis Stars Evolve from a White Dwarf Merger rather than a Final Helium Shell Flash

Details Evidence that R Coronae Borealis Stars Evolve from a White Dwarf Merger rather than a Final Helium Shell Flash Evidence that R Coronae Borealis Stars Evolve from a White Dwarf Merger rather than a Final Helium Shell Flash

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...20916812c&link_type=abstract

2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #168.12; Bulletin of the American Astronomical Society,

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We have discovered, mainly using Gemini/GNIRS, that several hydrogen-deficient carbon (HdC) and R Coronae Borealis (RCB) stars, have 18O/16O ratios close to and sometimes exceeding unity, a value orders of magnitude greater than measured in other known stars (the Solar value is 1/500). This discovery is an important step in determining the evolutionary pathway of HdC and RCB stars in general, for which two models have been proposed: double degenerate (white dwarf (WD) merger), and the final helium-shell flash (FF). The FF model for producing RCB stars has been discredited recently due to a mismatch of abundances and timescales needed to produce the RCB stars. We have explored the idea that HdC and RCB stars originate in the merger of COand He-WDs in the light of the new observations. Understanding the RCB and HdC stars is a key test for any theory that aims to explain hydrogen deficiency in post-AGB stars. These new results on the 18O/16O ratio and our work on the FF star V605 Aql represent an opportunity for a huge breakthrough. Confirmation of the WD merger scenario, which is suggested, by both the models and these observations, will allow the use of RCB and HdC stars as probes for WD merger simulations. The ability to model the rates of these low-mass WD mergers will help us to understand the rates of more massive mergers that may make some type Ia supernovae.

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