NOAO >   Observing Info >   Approved Programs >   2009B-0302

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Proposal Information for 2009B-0302


PI: Geoffrey Clayton, Louisiana State University, gclayton@fenway.phys.lsu.edu
Address: Physics Department, Nicholson Hall, Baton Rouge, LA 70803, United States

CoI: Tom Geballe, Gemini Observatory
CoI: Joel Tohline, Louisiana State University
CoI: Falk Herwig, University of Victoria
CoI: Chris Fryer, LANL

Title: A Study of the 18O/16O Ratio of R Coronae Borealis Stars in the in Magellanic Clouds

Abstract: We have found that at least seven Galactic hydrogen-deficient carbon (HdC) and R Coronae Borealis (RCB) stars, have ^16O/^18O ratios close to and in some cases less than unity, values that are orders of magnitude lower than measured in other stars (the Solar value is 500). These discoveries are important clues in 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. We have quantitatively explored the idea that HdC and RCB stars originate in the mergers of CO- and He-WDs. Overall our analysis shows that RCB stars may be produced by WD mergers, which may be the low- mass counterparts of the more massive mergers thought to produce type Ia supernovae. We are requesting time using OSIRIS/SOAR to investigate the ^16O/^18O ratios for a sample of RCB stars in the LMC and SMC. These new data will allow us to investigate whether this ratio varies with galaxy metallicity and will provide important new constraints on our WD merger and nucleosynthesis models. The addition of Magellanic RCB stars is of great value because distances and absolute luminosities for the Galactic RCB stars are very uncertain.


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