Spitzer Space Telescope - General Observer Proposal #50059


Direct Observations of Clouds on Brown Dwarfs: A Spitzer Study of Extreme Cases

Principal Investigator: Adam Burgasser
           Institution: Massachusetts Institute of Technology

     Technical Contact: Adam Burgasser, Massachusetts Institute of Technology

Co-Investigators: 
Michael Cushing, U. Arizona                                           
Kelle Cruz, American Museum of Natural History                        
Mark Marley, NASA AMES                                                
Didier Saumon, Los Alamos National Laboratories                       
Dagny Looper, U. Hawaii                                               
Patrick Lowrance, SSC                                                 
J. Davy Kirkpatrick, Caltech/IPAC                                     

Science Category: brown dwarfs/very low mass stars 
 Observing Modes: IracMap IrsStare 
  Hours Approved: 14 

Abstract:
Clouds play a fundamental role in the emergent spectral energy distributions and
observed variability of very low mass stars and brown dwarfs, yet hey have only
been studied indirectly thus far. Recent indications of a broad silicate grain
absorption feature in the 8-11 micron spectra of mid-type L dwarfs, and evidence
that the strength of this absorption varies according to broad-band
near-infrared color, may finally allow the first direct studies of clouds and
condensate grain properties in brown dwarf atmospheres. We propose to observe a
sample of 18 ``extreme'' L dwarfs - objects with unusually blue and red
near-infrared colors - with IRAC and IRS to study the 8-11 micron feature in
detail (including grain size distributions and bulk compositions), and to
constrain advanced condensate cloud atmosphere models currently in development.
Our program provides a unique examination of the general processes of cloud
formation by focusing on the relatively warm photospheres of late-type brown
dwarfs.