AAS 207th Meeting, 8-12 January 2006
Session 110 Space-based Extra-Solar Planets: MOST, SPITZER, KEPLER, MPF
Poster, Wednesday, 9:20am-6:30pm, January 11, 2006, Exhibit Hall

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[110.03] Spitzer IRS Spectra of Ultracool Dwarfs

M.C. Cushing (Steward Observatory), T.L. Roellig (NASA Ames), Dim Suns Team

We present the first mid-infrared spectra of a sample of low-mass stars and brown dwarfs. These data were obtained with the Infrared Spectrograph onboard the Spitzer Space Telescope as part of the 'Dim Suns' Guaranteed Time Observing program. As expected from the predictions of model atmospheres, the spectra exhibit absorption bands of H2O at 6.5 microns, CH4 at 7.8 microns, and NH3 at 10.5 microns. Indeed these observations provide the first secure detection of NH3 in the atmospheres of brown dwarfs. We also compare the spectra to the latest atmospheric models that include the formation of condensate clouds and find good agreement between the models and the data. Finally we discuss a number of interesting objects that show peculiar spectral features.

M.C.C. acknowledges financial support through the Spitzer Space Telescope Fellowship Program.

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