Spitzer Space Telescope - Directors Discretionary Time Proposal #80233


Parallaxes for the Coldest WISE Brown Dwarfs


Principal Investigator: Trent Dupuy
           Institution: Smithsonian Astrophysical Observatory

     Technical Contact: Trent Dupuy, SAO

Co-Investigators: 
Adam Kraus, University of Hawaii
Michael Liu, University of Hawaii

Science Category: brown dwarfs/very low mass stars
 Observing Modes: IRAC Post-Cryo Mapping
  Hours Approved: 27.4

Abstract:
Understanding extremely low temperature atmospheres is a major goal of 
current studies of both brown dwarfs and exoplanets. Two weeks ago, 
Cushing et al. (2011) announced the first unambiguous sample of Y dwarfs, 
brown dwarfs showing clear signatures of ammonia in their NIR spectra. 
These objects are spectroscopically estimated to have temperatures of 
~300-500 K, colder than any previously known free-floating brown dwarfs. 
However, direct distances are needed to determine model-independent 
temperatures for this sample and to test their observed properties against 
current theoretical models in this new physical frontier. We propose to 
use Spitzer to measure trigonometric parallaxes for these objects, made 
possible thanks to their bright mid-IR emission and our improved distortion 
solution for IRAC. The >2-year time baseline achieved by combining our new 
Spitzer data from 2012 with WISE+Spitzer data from 2010 will enable us to 
robustly break the degeneracy between parallax and proper motion, resulting 
in distance errors of 10-20% and corresponding temperature uncertainties of 
30-50 K. Our distances will also enable fundamental tests of theoretical 
models by placing these coldest brown dwarfs on the color-magnitude diagram, 
where they are expected to lie ~5-10 mag below previously known objects 
at near-IR wavelengths.