Galactic planetary nebulae with Wolf-Rayet nuclei. II. A consistent observational data set

摘要

We present high resolution spectrophotometric data for 34 galactic planetarynebulae with [WC] nuclei (WRPNe).The sample includes PNe with early and late[WC] stars and some WELS. Physical conditions and chemical abundances have beenderived and expansion velocities were estimated for most objects of the sample.A statistical study was developed to find fundamental relationships between thenebular and central star parameters.We found evidence for a strong unexpectedelectron temperature gradient in WRPNe which is related to nebular excitation.Abundance ratios indicate that there seems to be no preferential stellar massfor the WR phenomenon to occur in the nucleus of a planetary nebula. The PNe M1-25 and M 1-32 were found to have very small Ne/O ratios.Our data confirm thetrend of the electron density decreasing with decreasing spectral type, whichwas interpreted as evidence that [WC] stars evolve from late to early [WC]types. On the other hand, the expansion velocities do not show the increasewith decreasing spectral type, that one might expect in such a scenario. Twoobjects with very late [WC] central stars, K 2-16 and PM 1-188, do not followthe general density sequence, being of very low density for their spectraltypes. We suggest that the stars either underwent a late helium flash (the``born again'' scenario) or that they have had a particularly slow evolutionfrom the AGB. The 6 WELS of our sample follow the same density vs. [WC]-typerelation as the bona fide WRPNe, but they tend to have smaller expansionvelocities. The comparison between the WRPNe in the Magellanic Clouds and inthe Galaxy indicates that metallicity affects the [WR] phenomenon in centralstars of planetary nebulae.