Chemical compositions and plasma parameters of planetary nebulae with Wolf-Rayet type central stars

P.Girard, J.Köppen, A.Acker

ABSTRACT Chemical compositions and other properties of planetary nebulae around central stars of spectral types [WC], [WO], and wels are compared with those of 'normal' central stars, in order to clarify the evolutionary status of each type and their interrelation. We use plasma diagnostics to derive from optical spectra the plasma parameters and chemical compositions of 48 WR planetary nebulae. We also reanalyze the published spectra of a sample of 167 non-WR PN. The results as well as the observational data are compared in detail with those from other studies of the objects in common. We confirm that [WC], [WO] and $wels$ nebulae are very similar to those 'normal' PN: the relation between [N II] and [O III] electron temperatures, abundances of He, N, O, Ne, S and Ar, and the number of ionizing photons show no significant differences. They also share very similar infrared (IRAS, DENIS) properties. The central star's spectral type is clearly correlated with electron density, temperature and excitation class of the nebula, [WC] nebulae tend to be smaller than the other types. All this corroborates the view of an evolutionary sequence from cool [WC 11] central stars inside dense, low excitation nebulae towards hot [WO 1] stars with low density, high excitation nebulae. The wels PN, however, appear to be a separate class of objects, not linked to WRPN by evolution: nebular excitation, electron temperature and density, and the number of ionizing photons all cover the whole range found in the other types. Their lower mean N/O ratio and slightly lower He/H suggest progenitor stars less massive than for the other PN types. Furthermore, the differences between results of different works are dominated by the differences in observational data rather than differences in the analysis methods.