PI: Geoffrey Clayton, Louisiana State University, email@example.com
Address: Dept. of Physics & Astronomy, Nicholson Hall, Baton Rouge, LA, 70803, USA
CoI: Tom Geballe, Gemini Observatory
CoI: Douglas Welch, McMaster University
CoI: Patrick Tisserand, Australian National University
Title: Using 16O/18O to Determine the Evolutionary History of the R Coronae Borealis Stars
Abstract: All of the Galactic hydrogen-deficient carbon (HdC) and R Coronae Borealis (RCB) stars for which oxygen isotopic ratios can be measured, show 16O/18O < 5, values that are orders of magnitude lower than measured in other stars (the Solar value is 500). This suggests that most if not all HdC and RCB stars are highly enriched in 18O. This is an important clue to determining the evolutionary pathways of HdC and RCB stars, for which two models have been proposed: the double degenerate (white dwarf (WD) merger), and the final helium-shell flash (FF). No overproduction of 18O is expected in the FF scenario. However, some RCB stars also show characteristics, such as 13C and Lithium, seen in FF stars. Therefore, we are conducting a survey of all the RCB stars in the LMC and SMC for the characteristics of a WD merger or a FF. Most of the stars have been surveyed for 13C already, and we are also planning to survey them for Lithium. But no RCB star in the Magellanic Clouds has been observed for 18O. The Magellanic Clouds provide an unbiased, relatively complete sample of RCB stars which are at a known distance so their bolometric luminosities can be used in our stellar evolution models. This proposal is to use Gemini/Flamingos-2 to survey all of the Magellanic Cloud stars, which are cool enough to show CO bands, for the presence of 18O near 2.3 micron. This survey, combined with our stellar evolution models, will reveal the true fraction of RCB stars formed by each of the proposed scenarios.
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