IMAGING OF DUST SHELLS AROUND AGB AND POST-AGB STARS openParPART 2closePar

we propose to study the mass loss phenomenon during the final phases of the asymptotic giant branch (agb) evolution. to resolve the mass loss history over the longest possible lookback times we need to map the cold (2030 k) and faint outer parts of the dust shells with the best possible sensitivity. this cannot be done from the ground; the iras data base and the kuiper airborne observatory do not have sufficient sensitivity. for our purposes isophotc is the instrument of choice. we will make very deep images at 90 and 160 microns of the extended dust shells around obscured agb stars and young postagb stars using oversampled raster maps (aot pht32). for sources at a typical distance of 0.5 kpc, the spatial resolution and sensitivity will be sufficient to study in detail the history of the agb mass loss with a time resolution of 3,000 yr and a lookback time of 1e5 yr (virgul12 thermal pulse cycles). in addition, the integrated dust distributions of the shells will provide much improved limits on their dust masses, a property which is much debated and poorly known. finally, the square maps will enable us to observe the dust shell morphology on the largest scales. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]