The rapid evolution of the born-again giant Sakurai's object

Abstract

The extraordinarily rapid evolution of the born-again giant Sakurai's object can be traced both in a continued cooling of the stellar surface and dramatic changes in chemical composition on a timescale of a mere few months. The abundance alterations are the results of the mixing and nuclear reactions which have ensued due to the final He-shell flash which occurred during the descent along the white dwarf cooling track. The observed changes in the H and Li abundances can be explained by ingestion and burning of the H-rich envelope and Li-production through the Cameron-Fowler mechanism. The rapidly increasing abundances of the light s-elements (including Sc) is consistent with current s-processing by neutrons released from the concomitantly produced 13C. However, the possibility that the s-elements have previously been synthesized during the AGB-phase and only mixed to the surface in connection with the final He-shell flash cannot be convincingly ruled out either. Since Sakurai's object shows substantial abundance similarities with the R CrB stars and has recently undergone RCrB-like visual fading events, the ``birth'' of an RCrB star may have been witnessed for the first time ever.