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Astron. Astrophys. 362, 1008-1019 (2000)


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Evolutionary status of hydrogen-deficient central stars of planetary nebulae

S.K. Górny and R. Tylenda

Copernicus Astronomical Center, Department for Astrophysics, Rabiaska 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)

© European Southern Observatory (ESO) 2000

Online publication: October 30, 2000

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