Spitzer Space Telescope - Guaranteed Time Observer Proposal #50350


Mass Loss from Classical Cepheids and their Progenitors II: IRAC Deep Search for
Extended Emission

Principal Investigator: Giovanni Fazio
           Institution: Harvard-Smithsonian Astrophysical Observatory

     Technical Contact: Massimo Marengo, Harvard-Smithsonian Center for Astrophysics

Co-Investigators: 
Massimo Marengo, Smithsonian Astrophysical Obs.                       
Nancy Evans, Smitsonian Astrophysical Obs.                            
Pauline Barmby, University of Western Ontario                         
Doug Welch, McMaster University                                       
Giuseppe Bono, INAF Oss. Astronomico di Roma                          
Martino Romaniello, ESO                                               
Edward Guinan, Villanova University                                   
Scott Engle, Villanova University                                     

Science Category: evolved stars/pn/sne 
 Observing Modes: IracMap 
  Hours Approved: 6.4 

Abstract:
Despite their importance as primary extragalactic distance indicators, there are
still unresolved mysteries in the understanding and modeling of Classical
Cepheids. In particular, there remains a discrepancy between measured masses and
masses from evolutionary and pulsational calculations, as evidenced by recent
results on Polaris. One possible explanation for this outstanding discrepancy is
mass loss. Our GO-3 Spitzer observations of a sample of Classical Cepheids have
revealed infrared excess around ~1/3 of our targets. This emission is spatially
extended around delta Cep, SZ Tau and RS Pup, and may be the elusive evidence,
missing until now, of significant mass loss through the Cepheid phase. To test
how common this phenomenon is for the Cepheid phase we propose deep IRAC imaging
of all the targets in our GO-3 sample. We will use these deeper and wider field
images to search for further extended emission. The frequency of this emission,
and the Cepheid characteristics with which it is associated (pulsation
amplitude, luminosity, binarity) will provide clues to the source: ongoing mass
loss or residual interstellar matter.