ISO-SWS Observations of Planetary Nebulae with [WR] Central Stars

Abstract

More than a thousand planetary nebulae (PN) are known in the Galaxy and almost 50 of them have central stars of Wolf-Rayet type (see Tylenda 1996 for a recent review). In the spectra of these central stars strong, broad emission lines of He, C and O caused by dense stellar winds are observed. Detailed analyses of the spectra shows that the atmospheres of these stars are practically hydrogen free with helium and carbon being the most abun dant elements (Leuenhagen et al. 1996, Leuenhagen 1997, Koesterke & Hamann 1997). The spectra of these central stars look very similar to the spectra of genuine, massive Population I Wolf-Rayet stars of the WC sub-type. In order to avoid confusion between these two groups the Wolf-Rayet type central stars of planetary nebulae are usually labeled with [WR] — putting the abbreviation in brackets (van der Hucht et al. 1981).