| Description |
A subset of Asymptotic Giant Branch (AGB) stars loses mass at a
very high rate. The dust effectively shields the radiation from the
central star, allowing water-ice to condense onto existing
silicate grains. Through the mass loss process, these stars
provide a siginificant fraction to the gas and dust mass
return to the interstellar medium. They are thought to be
massive intermediate-stars (>5 Msun), close to the end of their AGB evolution.
Using Herschel to obtain the full spectral
coverage from 50 to 670 micron with PACS and SPIRE, we will obtain
spectra of gas-phase H2O lines and derive the H2O
abundance by modelling these lines, thought to be the main
cooling agent in O-rich AGB star.
This, combine with a few selected high resolution
observations 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 region
close to the central star and detect any departure from spherical
symmetry in the structure of the CSE. We will also get a handle on
the stellar mass from 12C/13C and the wealth of the
molecular emission lines in this wavelength range will be used to
study the ongoing chemistry in highly obscured circumstellar
envelopes of AGB stars. |
