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

We present high resolution spectrophotometric data for a sample of 34 plane tary nebulae with [WC] spectral type central stars (WRPNe) in our Galaxy. T he observed objects cover a wide range in stellar characteristics: early an d late [WC] type stars, as well as:weak-emission line stars (WELS). Physica l conditions in the nebulae (electron density and temperatures) have been o btained from various diagnostic line ratios, and chemical abundances have b een derived with the usual empirical scheme. Expansion velocities were esti mated in a consistent manner from the line profiles for most objects of the sample. A statistical study was developed for the derived data in order to find fundamental relationships casting some light on the evolutionary stat us of WRPNe. We found evidence for a strong electron temperature gradient i n WRPNe which is related to nebular excitation. Such a gradient is not pred icted in simple photoionization models. Abundance ratios indicate that ther e seems to be no preferential stellar mass for the Wolf-Rayet phenomenon to occur :in the nucleus of a planetary nebula. Two objects, M 1-25 and M 1-3 2, were found to have a very small Ne/O ratio, a property difficult to unde rstand. We reexamined the relation between the nebular properties of the WR PNe and the spectral types of the central stars. Our data confirm the trend found by other authors of the electron density decreasing with decreasing spectral type, which was interpreted as evidence that [WC] stars evolve fro m late to early [WC] types. On the other hand, our data on the expansion ve locities do not show the increase of expansion velocity with decreasing spe ctral type, that one might expect in such a scenario. Two objects with very late [WC] type central stars, K 2-16 and PM 1-188, do not follow the gener al density sequence, being of very low density for their spectral types. We suggest that the stars either underwent a late helium flash (the "born aga in" scenario) or that they have had a particularly slow evolution from the AGE. Tile 6 WELS of our sample follow the same density vs. [WC]-type relati on as the bona fide WRPNe, but they tend to have smaller expansion velociti es. Considerations about the evolutionary status of WELS must await the con stitution of a larger observational sample. The analysis of the differences between the WRPNe in the Magellanic Clouds (distribution of [WC] spectral types, N/O ratios) and in the Galaxy indicates that metallicity affects the [WR] phenomenon in central stars of planetary nebulae.