Dust Formation around R Coronae Borealis Stars: where is the Co?

Details Dust Formation around R Coronae Borealis Stars: where is the Co? Dust Formation around R Coronae Borealis Stars: where is the Co?

Dec 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997hst..prop.7477c&link_type=abstract

HST Proposal ID #7477

Physics

Hst Proposal Id #7477 Cool Stars

Scientific paper

It has been known for 60 years that the declines of R Coronae Borealis {RCB} stars are caused by circumstellar dust formation. The declines occur suddenly and without warning. No spectroscopic changes have yet been noted near the beginning of the decline, which might be linked to the cooling gas that must be condensing to form the dust. The mechanism of mass loss and dust formation is still a mystery. New observational evidence along with models of the carbon chemistry around RCB stars suggest that dust may condense close to the star. Shocks propagating through the outer atmospheres encourage non-equilibrium conditions where the conditions for carbon nucleation may be present. We propose to use STIS to search for a spectroscopic signature of the dust formation in these enigmatic stars, namely carbon monoxide {CO} emission in the UV. This abundant molecule is thought to be a critical gas coolant, yet CO has never been detected in an RCB star. V854 Cen and RY Sgr are the only two RCB stars with well defined pulsation cycles, linked to the time of dust formation. Spectra of these stars will be obtained at phase 0.0 of their pulsation cycles, 43.2 and 37.8 days, respectively when we know dust is forming. HST is required to obtain the ultraviolet spectra for this program. The program can be carried out equally well when the star is at maximum light or in decline, and there are 8 pulsation cycles of each star per year available for scheduling purposes.

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