Moderate‐ResolutionSpitzerInfrared Spectrograph Observations of M, L, and T Dwarfs

We present 10 - 19 um moderate resolution spectra of ten M dwarfs, one Ldwarf, and two T dwarf systems obtained with the Infrared Spectrograph (IRS)onboard the Spitzer Space Telescope. The IRS allows us to examine molecularspectroscopic features/lines at moderate spectral resolution in a heretoforeuntapped wavelength regime. These R~600 spectra allow for a more detailedexamination of clouds, non-equilibrium chemistry, as well as the molecularfeatures of H2O, NH3, and other trace molecular species that are the hallmarksof these objects. A cloud-free model best fits our mid-infrared spectrum of theT1 dwarf epsilon Indi Ba, and we find that the NH3 feature in epsilon Indi Bbis best explained by a non-equilibrium abundance due to vertical transport inits atmosphere. We examined a set of objects (mostly M dwarfs) in multiplesystems to look for evidence of emission features, which might indicate anatmospheric temperature inversion, as well as trace molecular species; however,we found no evidence of either.Comment: 19 pages, 7 figures, accepted ApJ 1/12/0