High-resolution imaging of dust shells - Asymmetries and temporal evolution

Advances in high-resolution imaging at visible, infrared, and radio wavelengths have allowed the circumstellar envelopes of evolved stars to be probed in unprecedented detail. While adequate to explain broadband spectral energy distributions, simplistic mass-loss scenarios (assuming spherical symmetry and continuous dust formation) have been shown to be grossly inadequate to understand the clumpy and often asymmetric dust shells recently revealed. In this paper, we will highlight a few sources that illustrate qualitatively new mass-loss phenomena, including the presence of circumstellar "disks" and evidence for sporadic, asymmetric mass ejections. Perhaps important physics is still missing from our picture of mass-loss on the AGB, for instance the effects of magnetic fields or large-scale convective motions.