Looking for Dual Dust Chemistry in the Shells of Hot R Coronae Borealis Stars

Details Looking for Dual Dust Chemistry in the Shells of Hot R Coronae Borealis Stars Looking for Dual Dust Chemistry in the Shells of Hot R Coronae Borealis Stars

May 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006sptz.prop30380c&link_type=abstract

Spitzer Proposal ID #30380

Physics

Scientific paper

Detecting the presence of dual dust chemistry will establish a definitive link between RCB stars and the [WC] central stars of PNe. More importantly, given the established relationship between dual dust chemistry and binarity, this program could be the first to firmly determine a link between the RCB phenomenon and binarity, constituting a large step towards resolving the origin of RCB stars and the phenomenon of H-deficiency on the AGB. The RCB stars are rare hydrogen-deficient carbon-rich supergiants, consistent with being post-AGB stars. Evolutionary scenarios have been suggested including, a merger of two stars, or a final helium shell flash. While most RCB stars are relatively cool (<7000 K), a few are significantly hotter (~20,000 K). Two of these stars, V348 Sgr and HV 2671 show similarities to the [WC] central stars of PNe such as CPD -56 8032, which shows RCB-like dust formation. CPD -56 8032 shows emission features of PAHs as well as crystalline silicates, indicating a dual dust chemistry, i.e., the simultaneous presence of both C-rich and O-rich dust. These systems may all be binaries in which the O-rich silicates are trapped in a disk as a result of a past mass transfer event, with the C-rich particles being more widely distributed in the nebula as a result of recent ejections of C-rich material. We will use the IRS to obtain spectra in the Short-Low and Long-Low modes to look for evidence of a similar dual dust chemistry in the shells of the two hot RCB stars, V348 Sgr and the LMC star, HV 2671. In the large nebula around V348 Sgr, we may be able to see a spatial separation between the O-rich dust in a disk close to the star and the C-rich dust spread through the nebula, which would strongly support the binary/disk model for dual dust chemistry. For a very small expenditure of Spitzer Space Telescope time, we may be able to provide for the first time a real connection between the RCB and [WC] central stars.

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