[WC] and PG1159 Central Stars of Planetary Nebula: the Need for an Alternative to the Born-Again Scenario

TL;DR

This paper questions the traditional born-again scenario for hydrogen-deficient central stars of planetary nebulae and proposes a binary interaction model as a more plausible explanation for their observed properties.

Contribution

It introduces a binary scenario involving a common envelope phase to explain hydrogen deficiency in central stars, challenging the conventional single-star born-again model.

Findings

Binary scenario can account for observed hydrogen deficiency

Common envelope evolution influences star's surface composition

Proposes an alternative to the born-again scenario for these stars

Abstract

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.