Hydrogen-deficient central stars of planetary nebula such as Wolf-Rayet and PG1159 central stars and some weak emission line stars are primarily composed of helium and carbon. This abundance is well explained by a scenario where a single post-AGB star experiences a last helium shell flash which ingests and burns, or simply dilutes, the remaining hydrogen atmosphere. But despite its success in matching the photospheric abundances of these stars, this scenario is faced with several observational challenges. A binary scenario is proposed here as a more natural way to face some of the most stringent observational constraints. In this scenario the H-rich primary in a close binary formed during a common envelope on the AGB, suffers a last helium shell flash, which results in a H-deficient primary with some of the characteristics needed to match the observations.
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