Spitzer Space Telescope - Guaranteed Time Observer Proposal #50692


The Silicate-Extinction Relationship in Filament L673

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

     Technical Contact: Tracy Huard, University of Maryland, College Park

Co-Investigators: 
Tracy Huard, University of Maryland                                   
Lori Allen, SAO                                                       
Klaus Pontoppidan, Caltech                                            
Jeff Bary, University of Virginia                                     
Jarron Leisenring, University of Virginia                             
Adwin Boogert, NASA Herschel Science Center                           
Claudia Knez, University of Maryland                                  

Science Category: ISM 
 Observing Modes: IrsStare 
  Hours Approved: 6.4 

Abstract:
We propose to obtain Spitzer IRS spectra of 18 background stars toward two cores
within the isolated dense filament L673. These stars were carefully selected to
probe a wide range of extinctions in the starless core L673-SMM4 and the
cluster-forming core L673-SMM1/2 in order to further investigate the
silicate-extinction relationship in dense, isolated environments. With the
primary goal of characterizing this relationship in different core environments,
a previous program (PID 40928) included 63 background stars sampling a wide
range of extinctions through four cores: a starless core, single-star-forming
core, cluster-forming core, and a core apparently exhibiting an anomalous
relationship. The additional observations proposed here would serve to (1)
provide a more robust characterization of differences between the
silicate-extinction relationship in starless and star-forming cores, and (2)
enable us to address whether this relationship is similar for cores of similar
star-formation rates. We have shown previously that the silicate-extinction
relationship is a sensitive probe of grain evolution, providing constraints on
the carbon-to-silicate composition and grain sizes, especially when combined
with 1-1000 micron observations.