Study of the cool forsterite dust around evolved stars

We propose to perform PACS range spectroscopy around the 69 micronforsterite dust feature of evolved stars. With the spectral resolutionand sensitivity of PACS weare able to fit the profile of the forsterite feature which is verysensitive to temperature and composition of the grain. Based on a sample, observed in earlier GT programmes, of about 15 evolved stars, including OH/IR stars, postAGB and PNs, we find that the olivinedust is purely Mgrich and contains no iron. We find differences betweenthe .outflow. sources and sources which have disks, likely indicating adifferent formation history. The modelling of the midinfrared bands (observed with SWS) in combination of the 69 micron band of the heavily obscured OH/IR stars allows to study the dust distribution and search for deviations fromspherical symmetry or changes in mass loss history. With the new observations of a new set of 13 stars we want to substantiate ourfindings. The combination of SWS and PACS spectroscopy will provide a legacydataset for future studies of crystalline dust. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]