A Model For the Formation of High Density Clumps in Proto-Planetary Nebulae

Abstract

The detection of NaCl at large radii in the Egg Nebula, CRL 2688, requires densities of 10^7 - 10^8 cm^-3 in a thick shell of r ~ a few X 10^17 cm. To explain these results, a mechanism is needed for producing high densities at a considerable distance from the central star. In two dimensional simulations of the interaction of the fast wind with an ambient medium, the material becomes thermally unstable. The resulting clumps can achieve the requisite conditions for NaCl excitation. We present 2D models with simple physics as proof-of-principle calculations to show that the clumping behavior is robust. Clumping is a natural outcome of cooling in the colliding wind model and comparable to that inferred from observations.

12 pages, 3 figures. Accepted for publication in the Astrophysical Journal Letters

References in corpus (4)

• High Resolution CO and H2 Molecular Line Imaging of a Cometary Globule in the Helix Nebula
• Observational Tests and Predictive Stellar Evolution
• Chemical Evolution of the Circumstellar Envelopes of Carbon-rich Post-AGB objects
• Stellar Hydrodynamics in Radiative Regions

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