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Astron. Astrophys. 362, 1008-1019 (2000)
Evolutionary status of hydrogen-deficient central stars of planetary nebulae
S.K. Górny and
R. Tylenda
Copernicus Astronomical Center, Department for Astrophysics, Rabia
ska 8, 87-100 Toru, Poland
Received 13 June 2000 / Accepted 4 September 2000
Abstract
The observational data for the planetary nebulae with hydrogen-deficient central stars are analysed. We show that the general evolutionary sequence is: late-[WC], early-[WC], PG 1159. An analysis of the observed distributions of nebular parameters leads to a conclusion that the planetary nebulae with hydrogen-deficient nuclei are not different from the population of other planetary nebulae in the Galaxy. In particular the proportion of the H-deficient stars among young nebulae is the same as in the whole population. We have made a detailed comparison of the observed parameters with theoretical modelling of the late He-shell flash (born again AGB) scenario. Our finding is that the [WC] nuclei are not formed in a late He-shell flash. This scenario can, however, give origin to some PG 1159 objects. There are five objects known which have presumably suffered from a late He-shell flash. The observed parameters of their nebulae imply that these stars will not become typical [WC] objects. Thus most of hydrogen-deficient central stars (at least [WC]) evolve directly from the AGB as do the other planetary nebula nuclei. We discuss implications of this result.
Key words: ISM: planetary nebulae:
general 
stars: AGB and
post-AGB
stars: Wolf-Rayet
Send offprint requests to: S.K. Górny (skg@ncac.torun.pl)
Contents
- 1. Introduction
- 2. Observational data and parameters
- 3. Evolutionary sequence of H-deficient PNNi
- 4. PNe with H-deficient central stars versus other PNe
- 5. Late He-shell flash scenario
- 6. Conclusions and discussion
- Acknowledgements
- References
© European Southern Observatory (ESO) 2000
Online publication: October 30, 2000
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