Sakurai’s Object, a Late He-Flash

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We report on dramatic change in Sakurai’s object (RA: 17h52m32.7s, DEC: −17d41’07”, J2000.0). Discovered by the Japanese amateur astronomer Y. Sakurai in Feb. 1996, this object was first classified as a slow nova (Nakano S., Sakurai Y., Hazen M., McNaught R.H., Benetti S., Duerbeck H.W., Leibundgut B., 1996, IAU Circ. 6322). Further study revealed a spectrum rich in C, N and O-lines, but poor in hydrogen, as well as an old planetary nebula surrounding the star; it was then realized that this might be a star undergoing a late He-flash (Benetti, S. et al. 1996, IAU Circ. 6325). Despite the fact that 10 to 20% of all low mass stars will experience a late He-flash (Iben I. Jr., MacDonald J., 1996), it is an extremely rare observational event, due to its short duration. The most recent example is V605 Aql/A58 in 1919 (Eitter W.C., 1987, ESO Messenger, 14: see also Clayton C.G., De Marco O., 1997, AJ for a review).

In March 1997 we discovered dramatic change in the optical spectrum of Sakurai’s object using the 2.5 m Du Pont telescope at Las Campanas, Chile. The dominating features now are the prominent bands of CN (bandheads at 388.8 and 421.6 nm) and C₂ (Swan-Bands at 439.2, 473.7, 516.5, 558.5 and 565.5 nm)(Kerber F., Gratl, H., Roth, M., 1997, IAU Circ. 6601) that were not evident a year ago (Duerbeck, H.W., Benetti, S., 1996, ApJ 468, L111).