A spectacular mass-loss event of the central star of Longmore 4.

Abstract

We report on a dramatic change in spectral type of the central star of the planetary nebula Longmore 4. Its 'low state' spectrum is that of a PG 1159 star, i.e., of an extremely hot hydrogen-deficient (pre-) white dwarf, whereas its 'high state' spectrum has to be classified as of early Wolf-Rayet type (WC2-3). The observed spectral change reveals a surprising and short-lived mass-loss event, which must have started after our first observation in May 1991 and which is observed during its rapid fading phase within a few days in January/February 1992. Longmore 4, like some other PG 1159 stars, is a non-radial g-mode pulsator, and the hypothesis of a correlation between these pulsations and the observed mass-loss event is proposed. Possible implications for the white dwarf evolution are briefly discussed.