Hydrogen-poor planetary nebulae |
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| Authors: | Albert A Zijlstra |
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| Institution: | (1) Department of Physics, UMIST, P.O. Box 88, Manchester, M60 1QD, UK |
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| Abstract: | Five planetary nebulae are known to show hydrogen-poor material nearthe central star. In the case of A58, this gas was ejected following alate thermal pulse similar to Sakurai's Object. In this paper I will reviewthese five objects. One of them, IRAS 18333 –2357, may not be a truePN. I will show that there is a strong case for a relation to the WC]stars and their relatives, the weak emission-line stars. The surfaceabundances of the WC] stars are explained via diffuse overshoot intothe helium layer. The hydrogen-poor PNe do not support this: theirabundances indicate a change of abundance with depth in the heliumlayer. A short-lived phase of very high mass loss, the r-AGB, isindicated. Sakurai's Object may be at the start of such a phase, and mayevolve to very low stellar temperatures. |
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| Keywords: | Planetary nebulae post-AGB evolution |
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