Astronomy and Astrophysics – Astrophysics
Scientific paper
2001-01-30
Astronomy and Astrophysics
Astrophysics
20 pages, including 2 figures and 3 tables. Paper accepted in Astronomy and Astrophysics, 2001
Scientific paper
10.1051/0004-6361:20000497
We present high resolution spectrophotometric data for 34 galactic planetary nebulae with [WC] nuclei (WRPNe).The sample includes PNe with early and late [WC] stars and some WELS. Physical conditions and chemical abundances have been derived and expansion velocities were estimated for most objects of the sample. A statistical study was developed to find fundamental relationships between the nebular and central star parameters.We found evidence for a strong unexpected electron temperature gradient in WRPNe which is related to nebular excitation. Abundance ratios indicate that there seems to be no preferential stellar mass for the WR phenomenon to occur in the nucleus of a planetary nebula. The PNe M 1-25 and M 1-32 were found to have very small Ne/O ratios.Our data confirm the trend of the electron density decreasing with decreasing spectral type, which was interpreted as evidence that [WC] stars evolve from late to early [WC] types. On the other hand, the expansion velocities do not show the increase with decreasing spectral type, that one might expect in such a scenario. Two objects with very late [WC] central stars, K 2-16 and PM 1-188, do not follow the general density sequence, being of very low density for their spectral types. We suggest that the stars either underwent a late helium flash (the ``born again'' scenario) or that they have had a particularly slow evolution from the AGB. The 6 WELS of our sample follow the same density vs. [WC]-type relation as the bona fide WRPNe, but they tend to have smaller expansion velocities. The comparison between the WRPNe in the Magellanic Clouds and in the Galaxy indicates that metallicity affects the [WR] phenomenon in central stars of planetary nebulae.
Medina S.
Peña Manuel
Stasinska Grazina
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