The rise and fall of V4334 Sagittarii (Sakurai's object)

CCD UBVRi photometry of the final helium flash object V4334 Sgr (Sakurai's object) carried out during 1997-1999 is presented, and the light curve from its prediscovery rise to the dust obscuration phase is constructed. The op tical light curve can be divided into four sections, the rise to maximum, t he maximum, the dust onset, and the massive dust shell phase. The color ind ices show a general increase with time, first because of the photospheric e xpansion and cooling and later because of the dust-forming events. The ener gy distributions for the years 1996-1999 show that an increasing part of th e energy is radiated at infrared wavelengths. In 1996 the infrared excess i s likely caused by free-free radiation in the stellar wind. Starting from 1 997 or 1998 at the latest, carbon dust grains are responsible for the more and more dramatic decrease of optical radiation and the growing infrared ex cess. Its photometric behavior in 1998-1999 mimics the "red declines" of R CrB variables; the amplitude, however, is more extreme than any fading ever observed in an R CrB star. Evidence is given that a complete dust shell ha s formed around V4334 Sgr. It therefore shows similarities with dust-formin g classical novae, although it is evolving similar to 20 times more slowly. Its luminosity increased by a factor 4 between 1996 and 1998. A comparison of timescales of the final helium flash objects FG Sge, V605 Aql, and V433 4 Sgr shows that the observed photometric and spectroscopic features are si milar, while V4334 Sgr is the most rapidly evolving object to date.