Spitzer Space Telescope - General Observer Proposal #50717


An Interferometric Snapshot Survey to Constrain Mass-Loss Dynamics and Physics
in AGB Stars

Principal Investigator: Michelle Creech-Eakman
           Institution: New Mexico Institute of Mining and Technology

     Technical Contact: Michelle Creech-Eakman, New Mexico Institute of Mining and Technology

Co-Investigators: 
Joseph Hora, Harvard-Smithsonian - CfA                                
Zeljko Ivezic, Univ of Washington                                     
Colby Jurgenson, Magdalena Ridge Observatory -- NMT                   
Don Luttermoser, East Tennessee State Univ.                           
Massimo Marengo, Harvard-Smithsonian CfA                              
Robert Stencel, Univ of Denver                                        
Robert Thompson, CHARA Array -- GSU                                   

Science Category: evolved stars/pn/sne 
 Observing Modes: IrsStare 
  Hours Approved: 25.6 

Abstract:
We propose Spitzer IRS observations of a unique sample of 25 AGB (mira) variable
stars with interferometrically determined K-band angular diameters and
spectrophotometry taken simultaneously using the Palomar Testbed Interferometer.
These high-resolution spectral and spatial observations, in conjunction with
amateur light-curves (e.g. AAVSO), will be used together to place constraints on
the location of the IR stellar photosphere and the nature of the molecules and
dust in the circumstellar environment (CSE). We can then develop complete models
of the stars and CSE, using our state-of-the-art hydrodynamic atmosphere codes
(ATLAS/PANDORA) and radiative transfer code (DUSTY). This will allow us to
undertake the most accurate modeling of these highly dynamic environments that
has yet been done for evolved stars. With results from these observations we
will answer several key questions about these stars including: 1) how important
are the roles of NLTE atmospheres in the formation of dust?; 2) what dust
species are relevant to a given AGB dust morphology and do these change as a
result of the pulsational cycle?; 3) is dust created or destroyed during the
pulsational cycle and how does this relate to the abundances of other molecules
in the CSE?; and finally, 4) what is the physical location of the dust
production around an AGB star which acts to define the age-dependent
spectral-energy distribution? These types of observations require a high-level
of spectroscopic fidelity, repeatability and sensitivity which is unable to be
executed under conditions of telluric contamination. Therefore these types of
observations can only be performed with Spitzer's IRS instrument.