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Title:
A Spitzer Infrared Spectrograph Spectral Sequence of M, L, and T Dwarfs [ Erratum: 2009ApJ...706..923C ]
Authors:
Cushing, Michael C.; Roellig, Thomas L.; Marley, Mark S.; Saumon, D.; Leggett, S. K.; Kirkpatrick, J. Davy; Wilson, John C.; Sloan, G. C.; Mainzer, Amy K.; Van Cleve, Jeff E.; Houck, James R.
Affiliation:
AA(Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721; Spitzer Fellow. ), AB(NASA Ames Research Center, Mail Stop 245-6, Moffett Field, CA 94035 ), AC(NASA Ames Research Center, Mail Stop 254-3, Moffett Field, CA 94035 ), AD(Los Alamos National Laboratory, Applied Physics Division, Mail Stop P365, Los Alamos, NM 87544 ), AE(Gemini Northern Operations, 670 North A'ohoku Place, Hilo, HI 96720 ), AF(Infrared Processing and Analysis Center, California Institute of Technology, Mail Stop 100-22, Pasadena, CA 91125 ), AG(Astronomy Building, University of Virginia, 530 McCormick Road, Charlottesville, VA 22903 ), AH(Astronomy Department, Cornell University, Ithaca, NY 14853 ), AI(Jet Propulsion Laboratory, Mail Stop 169-506, 4800 Oak Grove Drive, Pasadena, CA 91109 ), AJ(Ball Aerospace and Technologies Corporation, 1600 Commerce Street, Boulder, CO 80301 ), AK(Astronomy Department, Cornell University, Ithaca, NY 14853 )
Publication:
The Astrophysical Journal, Volume 648, Issue 1, pp. 614-628. (ApJ Homepage)
Publication Date:
09/2006
Origin:
UCP
Astronomy Keywords:
Infrared: Stars, Stars: Late-Type, Stars: Low-Mass, Brown Dwarfs
DOI:
10.1086/505637
Bibliographic Code:
2006ApJ...648..614C

Abstract

We present a low-resolution (R≡lambda/Deltalambda~90), 5.5-38 mum spectral sequence of a sample of M, L, and T dwarfs obtained with the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope. The spectra exhibit prominent absorption bands of H2O at 6.27 mum, CH4 at 7.65 mum, and NH3 at 10.5 mum and are relatively featureless at lambda>~15 mum. Three spectral indices that measure the strengths of these bands are presented; H2O absorption features are present throughout the MLT sequence, while the CH4 and NH3 bands first appear at roughly the L/T transition. Although the spectra are, in general, qualitatively well matched by synthetic spectra that include the formation of spatially homogeneous silicate and iron condensate clouds, the spectra of the mid-type L dwarfs show an unexpected flattening from roughly 9 to 11 mum. We hypothesize that this may be a result of a population of small silicate grains that are not predicted in the cloud models. The spectrum of the peculiar T6 dwarf 2MASS J0937+2931 is suppressed from 5.5 to 7.5 mum relative to typical T6 dwarfs and may be a consequence of its mildly metal-poor/high surface gravity atmosphere. Finally, we compute bolometric luminosities of a subsample of the M, L, and T dwarfs by combining the IRS spectra with previously published 0.6-4.1 mum spectra and find good agreement with the values of Golimowski et al., who use L'- and M'-band photometry to account for the flux emitted at lambda>2.5 mum.

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