Spitzer Space Telescope Observations of M, L, and T Dwarfs

We present the first mid-infrared spectra of very low-mass stars and brown dwarfs obtained with the Infrared Spectrograph onboard the Spitzer Space Telescope. We observed GJ 1001 A (M3.5 V), DENIS 0255-4700 (L8), and ɛ Ind Ba/Bb (T1/T6). As expected from the predictions of model atmospheres, the spectra show absorption features of H₂O, CH₄ at 7.8 μm, and NH₃ at 10.5 μm. This is the first detection of the 7.8 μm CH₄ band in the spectrum of a brown dwarf and the first detection of NH₃ in the atmosphere of a brown dwarf.