Surface compositions of R coronae borealis stars and extreme helium stars - some connections

Abstract

Abundances of R Coronae Borealis stars (RCBs) and Extreme Helium stars (EHes) are discussed. Recent estimates of the s-process elements in hot extreme helium stars show enhancements of lighter s-process elements (Y, Zr) relative to heavier s-process elements, a characteristic shared by RCB stars. It also suggests that at least some EHe stars went through an episode of s-process element synthesis in their earlier evolution. A majority of RCB stars show a high 12C/13C ratio in their atmospheres. A recent analysis of the spectrum of minority RCB star VCrA, however, shows a lower value between 4 - 10. The implications of these results are discussed.