Spitzer Space Telescope - Guaranteed Time Observer Proposal #30179


T Dwarf Variability

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

Co-Investigators: 
Brian Patten, Smithsonian Astrophysical Observatory                   
Joseph Hora, Smithsonian Astrophysical Observatory                    
Massimo Marengo, Smithsonian Astrophysical Observatory                
John Stauffer, Spitzer Science Center                                 
Kevin Luhman, Penn State University                                   

Science Category: brown dwarfs/very low mass stars 
 Observing Modes: IracMap 
  Hours Approved: 7.0 

Abstract:
We are proposing to use IRAC to conduct a variability study of seven T
dwarfs covering a variety of mid- to late-T dwarf spectral sub-types
to assess the amplitude of variability over time scales of days,
weeks, months, and years.  This study of T dwarf variability in the
mid-IR will address three questions:  (1) what is the amplitude of
variability seen for T dwarfs across a wide variety of temperatures?,
(2) what is the time scale of the variability (i.e.  is it primarily
rotationally modulated (hours)) or do longer time scales (weeks,
months, years) related to slower atmospheric changes dominate?, and
(3) how much of the observed scatter in T dwarf colors, as observed by
IRAC, could be due to variability?  Ultimately we hope to determine
whether T dwarfs have relatively featureless atmospheres or have more
in common with giant planet atmospheres.  The monitoring campaign
being proposed here is the first step in determining level of
variability that can be seen in the T dwarfs in the mid-IR as a part
of evaluating the feasibility of future long-term monitoring of these
objects with IRAC.