Volume 520, September-October 2010
|Number of page(s)||4|
|Published online||28 September 2010|
Letter to the Editor
Photodissociation in proto-planetary nebulae
Hydrodynamical simulations and solutions for low-velocity multi-lobes
Instituto de Astronomía-UNAM, Apdo Postal 106, Ensenada 22800, Baja California, Mexico e-mail: firstname.lastname@example.org
Accepted: 9 September 2010
Aims. 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.
Methods. We perform two-dimensional gasdynamical simulations to model the effects of photodissociation in proto-planetary nebulae.
Results. We find that post-asymptotic giant branch stars with ~7000 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.
Conclusions. 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.
Key words: hydrodynamics / stars: AGB and post-AGB / planetary nebulae: general
© ESO, 2010
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