Spitzer Space Telescope - General Observer Proposal #3259


Mid-Infrared Spectroscopy of the Coldest Known Brown Dwarf 2MASS
0415-0935:  Physical Diagnostics and Spectral Modeling

Principal Investigator: Adam Burgasser
           Institution: Massachusetts Institute of Technology

Co-Investigators: 
Derek Homeier, University of Georgia                                  
J. Davy Kirkpatrick, IPAC/Caltech                                     
Peter Hauschildt, Universitat Hamburg                                 
France Allard, Ecole Normale Superieure                               
Ian McLean, UCLA                                                      

Science Category: brown dwarfs/very low mass stars 
 Observing Modes: IrsStare 
  Hours Approved: 1.2 

Abstract:
We propose to obtain 5-22 micron low-resolution spectroscopy for the
coldest known brown dwarf, 2MASS 0415-0935, using the IRS instrument
on Spitzer.  With an effective temperature of ~700-800  K, this source
is a benchmark for the study of low temperature atmospheres and a key
starting point for the search for even cooler brown dwarfs.  The
proposed observations will sample the brightest continuum emission
region for this object and resolve many individual molecular features,
including the important 10.5 micron band of NH3, the only detectable
nitrogen-bearing molecule in a brown dwarf atmosphere and a tracer of
atmospheric dynamics.  By combining the Spitzer data with high
signal-to-noise, moderate resolution optical (0.6-1.0  micron) and
near-infrared (1.0-2.4 micron) ground-based data already obtained by
our group, and matching to our state-of-the-art spectral models, we
will be able to derive the physical properties of this source
(temperature, surface gravity, and metallicity), as well as test
current opacity models for H2O, CH4, and NH3, critical for modeling
and interpreting brown dwarf and planetary atmospheres.  The proposed
program is a focused experiment for measuring the physical parameters
of the coolest brown dwarfs now known and soon to be discovered, and
provides a key empirical test of atmosphere models used for both
substellar and planetary studies.