The emergence of a [WC] star in Sakurai's object

Sakurai's object provides a rare opportunity to observe stellar evolution on human timescales. Since its born-again event and detection in 1996, its evolution has been extensively monitored, and recent optical spectroscopy has suggested the emergence of [WR]-type emission features. In this Letter, we present a secure spectroscopic identification of its central star based on new VLT/FORS2 observations and NLTE expanding atmosphere models. Several observed emission lines arise in a [WR]-type stellar wind, establishing the central star as a [WR] object. The strongest stellar features are due to C II-III and He I. We derive the stellar and wind parameters of Sakurai's object and discuss its evolutionary status. The [WR] star is much cooler (Teff 30.5 kK) than the born-again star V605 Aql (Teff 95 kK), which erupted about 80 years earlier. The inferred temperature is lower than predicted by models suppressing convective mixing efficiency during the VLTP, but is consistent with higher time-resolution calculations involving slightly lower-mass (< 0.6Msun) remnants. Continued spectroscopic monitoring and atmospheric modelling will be crucial for tracing its reheating curve and constraining the physics of this rapid evolutionary phase.