Strong helium 10830Å absorption in Sakurai's object (V4334 Sgr)

Abstract

We report the appearance and evolution during 1998 of strong neutral helium ^3S-^3P^o absorption at ~10830Å in Sakurai's Object (V4334 Sgr), which is believed to be a planetary nebula nucleus (PNN) undergoing a final helium shell-flash. First detected on 1998 March 18, the profile of the Hei feature is P Cygni-like. The absorption depth has increased in three subsequent spectra in 1998. If this is owing to a wind, the profile indicates a wind velocity of ~670+/-50kms^-1. The strong Ci 10690-Å line seen prior to the appearance of the helium feature has disappeared; however Srii and CN absorption features remain present. We tentatively identify several new features as Sii. Taken together with other observations we suggest that the data are consistent with Sakurai's Object entering a phase in which it seems to have become a member of the R Coronae Borealis-type class of stars.