The Rise and Fall of V4334 Sagittarii (Sakurai’s Object)

CCD UBVRi photometry of the final helium flash object V4334 Sgr (Sakurai'sObject), carried out during 1997 - 1999, is presented, and the light curve fromits pre-discovery rise to the dust obscuration phase is constructed. Theoptical light curve can be divided into four sections, the rise to maximum, themaximum, the dust onset, and the massive dust shell phase. The color indicesshow a general increase with time, first because of the photospheric expansionand cooling, and later because of the dust forming events. The energydistributions for the years 1996 - 1999 show that an increasing part of theenergy is radiated at infrared wavelengths. In 1996, the infrared excess islikely caused by free-free radiation in the stellar wind. Starting from 1997 or1998 at the latest, carbon dust grains are responsible for the more and moredramatic decrease of optical radiation and the growing infrared excess. Itsphotometric behavior in 1998 - 1999 mimics the ``red declines'' of R CrBvariables, the amplitude, however, is more extreme than any fading everobserved in an R CrB star. Evidence is given that a complete dust shell hasformed around V4334 Sgr. It therefore shows similarities with dust-formingclassical novae, although evolving ~20 times more slowly. Its luminosityincreased by a factor 4 between 1996 and 1998. A comparison of time scales ofthe final helium flash objects FG Sge, V605 Aql and V4334 Sgr shows that theobserved photometric and spectroscopic features are similar, while V4334 Sgr isthe most rapidly evolving object to date.Comment: 27 pages, including 5 tables and 9 figures, LaTeX, accepted by the Astronomical Journal (scheduled for May, 2000