| Description |
A subset of Asymptotic Giant Branch (AGB) stars loses mass at avery high rate. The dust effectively shields the radiation from thecentral star, allowing water-ice to condense onto existingsilicate grains. Through the mass loss process, these starsprovide a siginificant fraction to the gas and dust massreturn to the interstellar medium. They are thought to bemassive intermediate-stars (>5 Msun), close to the end of their AGB evolution.Using Herschel to obtain the full spectralcoverage from 50 to 670 micron with PACS and SPIRE, we will obtainspectra of gas-phase H2O lines and derive the H2Oabundance by modelling these lines, thought to be the maincooling agent in O-rich AGB star.This, combine with a few selected high resolutionobservations of CO lines with HIFI will allow us to explore both the temperature and density structures of the circumstellar envelope (CSE). These observations will enable us to study the H2O abundance as a function of distance from the star as well as explore the superwind regionclose to the central star and detect any departure from sphericalsymmetry in the structure of the CSE. We will also get a handle onthe stellar mass from 12C/13C and the wealth of themolecular emission lines in this wavelength range will be used to study the ongoing chemistry in highly obscured circumstellar envelopes of AGB stars. |
