Program: GN-2015A-FT-5

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. Evidence pointing toward a WD merger or a final flash origin for RCB stars is contradictory. The RCB star SU Tau is currently about 9 magnitudes below its maximum V-band brightness of 9.5 mag. We are proposing for Gemini/GMOS imaging to resolve the nebulosity close to the central star, which is normally hidden when the star is bright. This will be accomplished by taking advantage of the natural coronagraph provided by SU Tau while in its deep decline. The unpredictable nature of these declines make these observations ideal for the new Fast Turnaround Observing Mode. We will also use Monte Carlo radiative transfer models to investigate the dust scattering in the shell to help determine its origin. 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.