NOAO >   Observing Info >   Approved Programs >   2012A-0222

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Proposal Information for 2012A-0222


PI: Geoffrey Clayton, Louisiana State University, gclayton@fenway.phys.lsu.edu
Address: Dept. of Physics & Astronomy, Baton Rouge, LA, 70803, USA

CoI: Tom Geballe, Gemini Observatory - North
CoI: Doug Welch, McMaster University
CoI: Patrick Tisserand, Mount Stromlo Observatory
CoI: Ben Sugerman, Goucher College
CoI: Howard Bond, Space Telescope Science Institute

Title: The Natural Coronographs of R Coronae Borealis Stars

Abstract: The R Coronae Borealis (RCB) stars are rare hydrogen-deficient carbon-rich supergiants. Two evolutionary scenarios have been suggested, a double degenerate merger of two white dwarfs (WDs), or a final helium shell flash. The evidence pointing toward a WD merger or a final flash origin for RCB stars is contradictory. A few show far-IR shells, cometary knots, or significant lithium in their atmospheres, consistent with a fossil planetary nebula (PN), supporting the scenario that RCB stars may be a product of a final flash. However, the high mass of the stars and their high 18O and fluorine abundances are more consistent with being the product of a WD merger. We are proposing a TOO program to take advantage of the natural coronograph of a deep decline in two RCB stars to obtain images with Gemini/GMOS to look for the presence of old PN shells that will help distinguish between the evolutionary scenarios. We will also use Monte Carlo radiative transfer models to investigate the dust scattering in the fossil shell. If the progenitors of RCB stars are close WD binaries, then they may be low-mass analogs of more-massive binaries destined to become Type Ia SNe.


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NOAO >   Observing Info >   Approved Programs >   2012A-0222

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