Patten, Brian M. and Stauffer, John R. and Burrows, Adam and Marengo, Massimo and Hora, Joseph L. and Luhman, Kevin L. and Sonnett, Sarah M. and Henry, Todd J. and Raghavan, Deepak and Megeath, S. Thomas and Liebert, James and Fazio, Giovanni G. (2006) Spitzer IRAC photometry of M, L, and T dwarfs. Astrophysical Journal, 651 (1). pp. 502-516. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20110727-073402473
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We present the results of a program to acquire photometry for 86 late M, L, and T dwarfs using the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. We examine the behavior of these cool dwarfs in various color-color and color-magnitude diagrams composed of near-IR and IRAC data. The T dwarfs exhibit the most distinctive positions in these diagrams. In M_(5.8) versus [5.8]-[8.0], the IRAC data for T dwarfs are not monotonic in either magnitude or color, giving the clearest indication yet that the T dwarfs are not a one-parameter family in T_(eff). Because metallicity does not vary enough in the solar neighborhood to act as the second parameter, the most likely candidate then is gravity, which in turn translates to mass. Among objects with similar spectral type, the range of mass suggested by our sample is about a factor of 5 (~70M_J to ~15M_J), with the less massive objects making up the younger members of the sample. We also find the IRAC 4.5 μm fluxes to be lower than expected, from which we infer a stronger CO fundamental band at ~4.67 μm. This suggests that equilibrium CH_4/CO chemistry underestimates the abundance of CO in T dwarf atmospheres, confirming earlier results based on M-band observations from the ground. In combining IRAC photometry with near-IR JHK photometry and parallax data, we find the combination of K_s, IRAC 3.6 μm, and 4.5 μm bands to provide the best color-color discrimination for a wide range of M, L, and T dwarfs. Also noteworthy is the M_k versus K_s-[4.5] relation, which shows a smooth progression over spectral type, and splits the M, L, and T types cleanly.
|Additional Information:||© 2006 The American Astronomical Society. Received 2006 March 28; accepted 2006 June 17. This work is based (in part) on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory (JPL), California Institute of Technology, under NASA contract 1407. Support for the IRAC instrument was provided by NASA under contract number 1256790 issued by JPL. We thank Sandy Leggett (our referee) and Adam Burgasser for providing us with insightful and helpful comments on our manuscript. This publication makes use of data from PAIRITEL, which is operated by the Smithsonian Astrophysical Observatory (SAO) and was made possible by a grant from the Harvard University Milton Fund, the camera loan from the University of Virginia, and the continued support of the SAO and the University of California, Berkeley. A. B. wishes to acknowledge NASA for its financial support via grant NNG 04GL22G. Furthermore, A. B. acknowledges support through Cooperative Agreement NNA 04CC07A between the University of Arizona/NOAO LAPLACE node and NASA’s Astrobiology Institute. This research has made use of the L and T dwarf compendium housed at DwarfArchives.org and maintained by Chris Gelino, Davy Kirkpatrick, and Adam Burgasser. This research also has made use of the SIMBAD database, operated at CDS, Strasbourg, France, and data from 2MASS, a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center. S. M. S. acknowledges support for this research by the SAO Summer Intern REU Program, funded by the National Science Foundation and the Smithsonian Institution.|
|Subject Keywords:||infrared: stars; stars: fundamental parameters; stars: late-type; stars: low-mass, brown dwarfs|
|Official Citation:||Spitzer IRAC Photometry of M, L, and T Dwarfs Brian M. Patten, John R. Stauffer, Adam Burrows, Massimo Marengo, Joseph L. Hora, Kevin L. Luhman, Sarah M. Sonnett, Todd J. Henry, Deepak Raghavan, S. Thomas Megeath, James Liebert, and Giovanni G. Fazio doi: 10.1086/507264|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||27 Jul 2011 15:05|
|Last Modified:||26 Dec 2012 13:25|
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