Cool Stars 14 - Submitted Abstract # 173
This version created on 05 October 2006

IRS Spectroscopy of 14 Late-L and T Dwarfs


Denise Stephens, Johns Hopkins University
David Golimowski, Johns Hopkins University
Didier Saumon, Los Alamos National Laboratory
Mark Marley, NASA Ames Research Center
Sandy Leggett, Gemini Observatory
Thomas Geballe, Gemini Observatory
Keith Noll, Space Telescope Science Institute
Xiaohui Fan, Steward Observatory

We will present infrared spectra from 5.2-14.5 microns for 14 late-L
and T dwarfs obtained with the Infrared Spectrograph (IRS) on the
Spitzer Space Telescope.  These spectra have been calibrated and
combined with published spectra from 1-2.5 microns taken by the UKIRT
and IRTF telescopes, and 3 of the objects have 3-4 micron spectra
obtained by us with the NIRI instrument on Gemini.  We fit these
spectra with synthetic spectra generated by state-of-the-art models,
developed by members of our team, that cover a range of effective
temperature, gravity, metallicity, grain sedimentation efficiency, and
vertical mixing efficiency.  We investigate the influence of these
parameters on the spectral energy distribution of each object.  The
observations presented here are unique from other surveys in that we
include several late-L dwarfs with very red or blue colors.  This lets
us place some constraints on the correlation between unusual
near-infrared colors and the effect of sedimentation efficiency on the
near- and mid-infrared spectra of the late-L dwarfs.  Evaluations of
photometry by our team have shown that the colors of late-L and T
dwarfs are only reproduced by models that include non-equilibrium
chemistry arising from vertical mixing (Leggett et al.  2006).  We
will extend that analysis to discuss the ways in which vertical mixing
impacts the spectra of these late-L and T dwarfs from 1-14.5 microns.

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