Evolution of Thin Gas Shells Along the AGB and Beyond

Abstract

Based on numerical simulations with two different computer codes, we have studied the time-dependent hydrodynamics of circumstellar gas/dust shells of AGB stars in their final stages of evolution. We discuss two different mechanisms capable of producing very thin shells of greatly enhanced gas density in the dusty outflows from these stars and illustrate their observable signatures. Our model calculations demonstrate that the thin shells produced on the AGB survive the transition to the post-AGB phase and can still be detected in the haloes of some Planetary Nebulae.