Program: GS-2003B-Q-23

The circumstellar envelopes (CSEs) of post-AGB stars provide a record of the mass-loss that occurred earlier on the AGB and which dominates the evolution of nearly all post-MS stars. In 2001A we used OSCIR on Gemini-N to obtain mid-IR images of 4 post-AGB CSEs, selected from our near-IR imaging polarimetry survey. By combining the mid- and near-IR data we are exploring, via detailed models, the CSE structure and composition, including dust density, grain sizes and degree of axisymmetry. This provides direct information on the evolution of mass-loss rates along the AGB, the dust formation process and the onset of axisymmetries that ultimately lead to the observed morphological diversity of PN. We propose to continue and extend this successful program to a further 8 targets using T-ReCS on Gemini-S. This is an updated resubmission of proposals G/02A/11 and G/02B/07 which were both approved but not observed due to the delay of T-ReCS.