gt00.html

Evolutionary status of hydrogen-deficient central stars of planetary nebulae.
Gorny S.K., Tylenda R.
2000, A&A 362, 1008

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.

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