Interpreting Form and Symmetry in Outflows from Geriatric Stars

Hubble images of post-AGB stars in the early stages of their mass loss are providing high-resolution (~100 AU) insights and constraints on their highly structured mass loss mechanisms.  Multi-epoch HST images are helping to probe the growth patterns of these objects.  (We shall briefly consider a few especially well-observed cases.)  However, this talk looks beyond the images to physics of the poutflows and what they suggest about the underlying and poorly understood ejection mechanisms  Our hydro models are revealing interpretive insights into the nature of the collimated flow patterns seen in the images above.  The nature of the mass ejection mechanisms and their collimation are now far better constrained, almost to the point of undermining the various ejection scenarios.