Abundance similarities between the RCrB star V854Cen and the born-again Sakurai's object

Abstract

The elemental abundances of the mildly hydrogen-deficient R Coronae Borealis (RCrB) star V854Cen have been estimated. The RCrB stars have been divided into majority and minority classes judging by their abundance patterns. Class assignment has previously been unambiguous but V854Cen has traits of both the minority and majority class. Neither V854Cen nor the three obvious minority members show any clear abundance signatures of having been affected by e.g. dust-gas separation as often observed in post-AGB stars. By chemical composition, V854Cen closely resembles Sakurai's object, which has probably recently experienced a final He-shell flash. Therefore V854Cen and Sakurai's object may share the same evolutionary background, which would add support for the final-flash scenario as a viable origin of the RCrB stars. Most of the few differences in abundance ratios between the stars could if so be attributed to milder H-ingestion in connection with the final He-shell flash of V854Cen. The identification of either the majority or the minority group, if any, as final flash objects, remain uncertain, however, due to the unclear membership status of V854Cen.