Shaping Planetary Nebulae: is it different for [WR] stars?

Abstract

This review discusses the physics of the formation of planetary nebulae around low mass WR stars, or [WR] stars. It especially focuses on the differences which can be expected due to the different character of the fast winds from these [WR] stars. Their fast winds are more massive and are highly H deficient and metal enriched compared to the winds of normal central stars of planetary nebulae. This is expected to lead to faster expansion velocities for the nebulae and a longer momentum-driven phase in the evolution of the wind-driven bubble, leading to more turbulent nebulae. The observational evidence also shows that the process which produces the [WR] stars is unlikely to influence the onset of aspherical mass loss, something which can be used as a test for models for aspherical mass loss from AGB and post-AGB stars. Finally it is shown that the nebular characteristics rule out a very late He shell flash as the origin of most [WR] stars.