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L. A. Valencic, R. Vazquez (IA-UNAM)
Interstellar dust is constantly being processed and recycled, from the time it forms in the outer atmospheres of evolved tars, to its injection into the ISM, to its accumulation in molecular clouds, and formation of planetary systems. Much grain formation occurs in the atmospheres of low-to-intermediate mass stars (0.8 \le M \le 8 M\odot) near the end of the asymptotic giant branch (AGB), where the extinction AV of the circumstellar dust cloud can be so high that only IR observations are possible. However, in the very rapid (~ 1000 yr) post-AGB or proto-planetary nebula phase, the dust shell detaches, cools, and dissipates, as photoionization has not yet begun. At this stage, investigations at short wavelengths become possible again, as the post-AGB star is much hotter than the AGB star, providing observers with an extrememly important window into the earliest stages of dust grain formation and subsequent evolution prior to its injection into the diffuse Galactic ISM. We are taking advantage of this and assembling data from the UV to IR on the shells of proto-planetary nebulae, including polarized near-IR imagery. This will allow us to understand not only the physical development of the dust shell's morphology, but also the evolution and processing of dust grains in this environment, by providing stringent, multi-wavelength constraints on models of grain development in shells.
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Bulletin of the American Astronomical Society, 37 #2
© 2005. The American Astronomical Soceity.