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Session 80 - Central Stars of Planetary Nebulae.
Display session, Wednesday, January 17
North Banquet Hall, Convention Center
We report recent spectacular changes in the WR spectrum of the central star of the planetary nebula LMC-N66. Before 1987, it showed a weak continuum with a T_eff \geq 120\,000 K and L_bol \simeq 25\,000 L_ødot. In 1990 the star began an intense mass-loss event and in a short time the continuum increased by a large factor and the absolute visual magnitude of the star changed from +1.24 in 1987 to -2.57 in January 1995. Simultaneously it developed impressive WR features (P-Cygni profiles in N\,V \lambda1240 and C\,IV \lambda1550 lines, wide He\,II emission, etc.) typical of a Population I WN4.5 star. The ejecta consisted of highly ionized He- and N-rich material (Peña et al., 1995, ApJ, 441, 343; Peña, 1995, RevMexAASC, 3, 215). These conditions remained with some variations for more than 5 years. Recent optical and UV data obtained by us show that the mass-loss has diminished abruptly in less than three months. The fast optically-thick wind has almost disappeared and the visual brightness of the central object has diminished in 2 magnitudes. Part of the ejected material was detected at much lower velocity, emitting in He\,II \lambda\lambda 6406, 6678, and other lines that disappeared in few days. The possibility of a fast recombination and cooling of the highly ionized ejecta is discussed.
Program listing for Wednesday