Spitzer Infrared Spectrograph (IRS) Observations of M, L, and T Dwarfs

We present the first mid-infrared spectra of brown dwarfs, together with observations of a low-mass star. Our targets are the M3.5 dwarf GJ 1001A, the L8 dwarf DENIS-P J0255� 4700, and the T1/T6 binary systemIndi Ba/Bb. As expected, the mid-infrared spectral morphology of these objects changes rapidly with spectral class because of the changes in atmospheric chemistry resulting from their differing effective temperatures and at- mospheric structures. By taking advantage of the unprecedented sensitivity of the Infrared Spectrograph on the Spitzer Space Telescope, we have detected the 7.8 � m methane and 10 � m ammonia bands for the first time in brown dwarf spectra.