Photodissociation in proto-planetary nebulae. Hydrodynamical simulations and solutions for low-velocity multi-lobes

Abstract

We explore the effects of photodissociation at the stages of post-asymptotic giant branch stars to find a mechanism able to produce multi-polar shapes. We perform two-dimensional gasdynamical simulations to model the effects of photodissociation in proto-planetary nebulae. We find that post-asymptotic giant branch stars with 7,000 K or hotter are able to photodissociate a large amount of the circumstellar gas. We compute several solutions for nebulae with low-velocity multi-lobes. We find that the early expansion of a dissociation front is crucial to understand the number of lobes in proto-planetary nebulae. A dynamical instability appears when cooling is included in the swept-up molecular shell. This instability is similar to the one found in photoionization fronts, and it is associated with the thin-shell Vishniac instability. The dissociation front exacerbates the growth of the thin-shell instability, creating a fast fragmentation in shells expanding into media with power-law density distributions such as r^-2.

4 pages, 2 figures, acepted by A&A Letters

References in corpus (5)

• Preplanetary Nebulae: An HST Imaging Survey and a New Morphological Classification System
• Multiple ring nebulae around blue supergiants
• Three-Dimensional Dynamical Instabilities in Galactic Ionization Fronts
• Astrophysical Explosions Driven by a Rotating, Magnetized, Gravitating Sphere
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