NOAO > Observing Info > Approved Programs > 2013B-0279
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NOAO > Observing Info > Approved Programs > 2013B-0279 |
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PI: Geoffrey Clayton, Louisiana State University, gclayton@fenway.phys.lsu.edu
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:
Of the Galactic hydrogen-deficient carbon (HdC) and R Coronae Borealis (RCB)
stars for which oxygen isotopic ratios can be measured, all of them 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 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. However, some RCB stars also show characteristics, such
as 13C and Lithium, seen in FF stars. Therefore, we are conducting a survey
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 plan to
survey them for Lithium in the future. This proposal is to use
Gemini/Flamingos-2 to survey all the stars, which are cool enough to show CO
bands, for the presence of 18O near 2.3 micron. 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 survey, combined with our models, will reveal the true
fraction of RCB stars formed by each of the proposed scenarios.
National Optical Astronomy Observatory, 950 North Cherry Avenue, P.O. Box 26732, Tucson, Arizona 85726, Phone: (520) 318-8000, Fax: (520) 318-8360
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NOAO > Observing Info > Approved Programs > 2013B-0279 |
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