| Description |
Mass loss is one of the most fundamental properties of post-mainsequence evolution. The mass-loss process leads to the formation ofcircumstellar shells containing dust and molecules. Although themass-loss phenomenon has been studied since the 1960s, and importantresults have been obtained with the IRAS, ISO and Spitzer spacemissions, the details of the mass-loss process and the formation andevolution of the circumstellar shells are still not wellunderstood. With its improved spatial resolution compared to ISO andSpitzer, better sensitivity, the extension tolonger and unexplored wavelength regions, and medium resolutionspectrometers, the combination of PACS and SPIRE observations willlead to a significant improvement in our understanding of thephenomena of mass loss and dust formation.The main aims of this programme are three-fold: (1) to study the timedependence of the mass loss process, via a search for shells andmultiple shells around a wide range of evolved objects, in order toquantify the total amounts of mass lost at the various evolutionarystages of low to high-mass stars, (2) to study the dust and gaschemistry as a function of progenitor mass, and (3) to study theproperties and asymmetries of evolved star envelopes.To this end, a sample of 103 Asymptotic Giant Branch and Red SuperGiants, post-AGB and Planetary Nebulae, Luminous Blue Variables andWolf-Rayet stars, and 5 Supernovae remnants will be imaged with PACSat 70+170 micron, and a sub-set of 32 stars will be imaged at all 3wavelengths with SPIRE.In spectroscopy, a sample of 55 stars will be observed over the fullwavelength range of PACS and, 23 stars will be observed with the SPIRE FTS.The sample of AGB stars has been selected to cover all chemical types(M-, S-, C-stars), variability types (irregular, semi-regular, Miras)and periods, and mass-loss rates. Stars have been selected to havehigh IRAS fluxes and low background levels. The spectroscopic targetsare typically the brightest of the mapping targets |
