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E.F. Guinan, L.E. DeWarf, G.P. McCook, P. DiTuro, R. Mittal (Villanova University), S.J. Margheim (Indiana University)
Pre-discovery observations show that Sakurai's Object (SO) had been a 21st mag central star of a faint planetary nebula (PN), which during late 1994 or early 1995 began to rapidly brighten. In February 1996, Y. Sakurai discovered the object as an 11th magnitude star. The star was first thought to be a slow nova, but later with more information, it was identified as a final helium flash object (see Duerbeck & Benetti 1996, ApJ 468, L111). The recent brightening occurs when the star descends the white dwarf cooling track and undergoes a final thermal pulse when the helium shell ignites causing it to expand rapidly to high luminosity and become a "born again" PN. This phase of stellar evolution is extremely short, lasting decades to centuries and would rarely be observed (Iben et al. 1983, ApJ 264,605).
UBVRI photometry of Sakurai's Object has been conducted with the Four College Consortium 0.8m APT from Arizona since the Spring of 1997. The APT photometry was combined with photometry made from other sites and light curves were formed. During 1996 the star steadily increased in brightness, rising from V = +11.4 to +10.9 mag. During 1997 the star remained bright, varying between +11.0 and +10.8 mag while at this time showing low amplitude (0.05-0.10 mag in V) semi-periodic light variations. However, in early 1998 it dropped to V ~ +12.6 mag. It then underwent slow oscillations in brightness - varying between +11.7 and +12.8 mag up to mid-1998. However, after August 1998, its brightness plummeted to below 15th mag. These dimming events were accompanied by increases in reddening and thus probably occurred as dust formed in the star's cooling outer atmosphere. The photometric behavior of Sakurai's Object appears to similar to that of another final flash candidate V605 Aql whose outburst and subsequent fading occurred during 1919-1923 (see Clayton & Marco, 1997, AJ, 114, 267).
This research is supported by NSF/RUI grants AST93-15365 and AST95-28506.