Spitzer Space Telescope - General Observer Proposal #3434


The Structure and Content of Pre-Stellar Massive Cores

Principal Investigator: Edwin Bergin
           Institution: University of Michigan

Co-Investigators: 
Lori Allen, Smithsonian Astrophysical Observatory                     
Tracy Huard, Smithsonian Astrophysical Observatory                    
David Wilner, Smithsonian Astrophysical Observatory                   

Science Category: young stellar objects 
 Observing Modes: IracMap MipsPhot 
  Hours Approved: 3.9 

Abstract:
Significant progress has been made in understanding the formation of
low-mass stars like the Sun through detailed studies of isolated
pre-stellar dense cores in nearby dark clouds.  Much less progress has
been made in understanding the formation of high-mass stars, in part
because they are intrinsically rare, short lived, and more distant,
but also because the initial phase-- the pre-stellar massive core --
has not been identified.  The recent MSX survey of the Galactic Plane
has allowed us to construct a catalog of 114 candidate pre-stellar
massive cores selected for high extinction (8 micron opacity),
proximity to known sites of high-mass star formation, and lack of
embedded sources.  We have imaged 50  of these candidates in various
molecular lines at millimeter wavelengths and find close
correspondence between the molecular emission and the dark patches of
extinction seen in the mid-infrared.  Because of selective depletion
of molecules onto cold dust grains, the chemical characteristics of
these regions provide an indicator of evolutionary state.  We propose
to use the Spitzer Space Telescope to observe a sample of these
candidate pre-stellar massive cores with the following goals:  (1) to
search for deeply embedded luminosity sources within the cores using
IRAC and MIPS to confirm that they do not harbor any stars to very low
luminosity limits, (2) to map the unknown physical structure of the
cores using IRAC images to measure extinction against background stars
as well as the diffuse Galactic background, and (3) to correlate the
derived physical structures of these cores with the known chemical
properties to place them in an evolutionary context, similar to that
of their low-mass brethren.