The Very Fast Evolution of the VLTP Object V4334 Sgr

Abstract

V4334 Sgr (Sakurai's object) is an enigmatic evolved star that underwent a very late thermal pulse a few years before its discovery in 1996. It ejected a new, hydrogen-deficient nebula in the process. Emission lines from the newly ejected gas were first discovered in 1998 (He I 1083 nm) and 2001 (optical). We have monitored the optical emission spectrum since. From 2001 through 2007 the optical spectrum showed an exponential decline in flux, consistent with a shock that occurred around 1998 and started cooling soon after that. In this paper we show that since 2008 the line fluxes have been continuously rising again. Our preliminary interpretation is that this emission comes from a region close to the central star, and is excited by a second shock. This shock may have been induced by an increase in the stellar mass loss and wind velocity associated with a rise in the stellar temperature.