Spitzer Space Telescope - General Observer Proposal #3167


The dust sequence along the AGB

Principal Investigator: Joris Blommaert
           Institution: Instituut voor Sterrenkunde Leuven

Co-Investigators: 
Jan Cami, NASA Ames Research Center                                   
Martin Groenewegen, Instituut voor Sterrenkunde Leuven                
Harm Habing, Observatory Leiden                                       
Ciska Kemper, UCLA Division of Astronomy                              
Alain Omont, Inst. d'Astrophysique Paris                              
Mathias Schultheis, Observatoire de Besancon                          
Xander Tielens, Kapteyn Institute                                     
Evelien Vanhollebeke, Instituut voor Sterrenkunde Leuven              
Rens Waters, Astronomical Institute 'Anton Pannekoek'                 
Peter Wood, Mt.Stromlo                                                

Science Category: evolved stars/pn/sne 
 Observing Modes: IrsStare 
  Hours Approved: 14.4 

Abstract:
The evolution of stars on the Asymptotic Giant Branch (AGB) is
characterized by substantial mass loss, producing large amounts of
circumstellar dust and a dust-driven outflow, which injects the
stellar ejecta into the interstellar medium.  Here we propose to
spectroscopically observe a homogeneous sample of AGB stars in the
Galactic bulge with Spitzer-IRS from 5.2 to 38 micron with the aim to
study the variations in dust composition for 1 solar mass stars as
they evolve along the AGB.  The Spitzer-IRS wavelength range 5.2 - 38
micron contains the major spectral features of aluminum oxides,
spinel, magnesium-iron oxides as well as those of amorphous and
various crystalline silicates.  Previous studies have shown these
components to be abundant in AGB environments, albeit with highly
varying relative abundances.  The stars in our sample all originate
from 1 solar mass stars, and only differ in their ages along the AGB.
Moreover, this sample fully covers the range in AGB mass-loss rates,
from the onset of mass loss on the AGB up to the superwind phase.  The
proposed observations with Spitzer-IRS will be coordinated with
ground-based observations to obtain simultaneous information on other
stellar parameters (such as pulsational phase).  With the proposed
observations we can therefore link for the first time the spectral
differences in dust composition directly to the age on the AGB.  Such
observations therefore offer the opportunity to comprehensively study
the composition and evolution of the circumstellar dust of a 1 solar
mass star as it climbs the AGB.  The proposed observations will
provide a unique observational baseline for studies of dust evolution
in AGB stars in our own and other galaxies.