The First Hundred Brown Dwarfs Discovered by the Wide-field Infrared Survey Explorer (WISE)

Creators: Kirkpatrick, J. Davy; Gelino, Christopher R.; Griffith, Roger L.; Marsh, Kenneth A.; Tsai, Chao-Wei; Beichman, Charles A.; Bridge, Carrie R.; Capak, Peter L.; Morales-Calderón, María; Manohar, Swarnima; Scoville, Nicholas Z.; Schurr, Steven D.

Abstract

We present ground-based spectroscopic verification of 6 Y dwarfs (see also Cushing et al.), 89 T dwarfs, 8 L dwarfs, and 1 M dwarf identified by the Wide-field Infrared Survey Explorer (WISE). Eighty of these are cold brown dwarfs with spectral types ≥T6, six of which have been announced earlier by Mainzer et al. and Burgasser et al. We present color-color and color-type diagrams showing the locus of M, L, T, and Y dwarfs in WISE color space. Near-infrared and, in a few cases, optical spectra are presented for these discoveries. Near-infrared classifications as late as early Y are presented and objects with peculiar spectra are discussed. Using these new discoveries, we are also able to extend the optical T dwarf classification scheme from T8 to T9. After deriving an absolute WISE 4.6 μm (W2) magnitude versus spectral type relation, we estimate spectrophotometric distances to our discoveries. We also use available astrometric measurements to provide preliminary trigonometric parallaxes to four of our discoveries, which have types of L9 pec (red), T8, T9, and Y0; all of these lie within 10 pc of the Sun. The Y0 dwarf, WISE 1541–2250, is the closest at 2.8^(+1.3)_(–0.6) pc; if this 2.8 pc value persists after continued monitoring, WISE 1541–2250 will become the seventh closest stellar system to the Sun. Another 10 objects, with types between T6 and >Y0, have spectrophotometric distance estimates also placing them within 10 pc. The closest of these, the T6 dwarf WISE 1506+7027, is believed to fall at a distance of ~4.9 pc. WISE multi-epoch positions supplemented with positional info primarily from the Spitzer/Infrared Array Camera allow us to calculate proper motions and tangential velocities for roughly one-half of the new discoveries. This work represents the first step by WISE to complete a full-sky, volume-limited census of late-T and Y dwarfs. Using early results from this census, we present preliminary, lower limits to the space density of these objects and discuss constraints on both the functional form of the mass function and the low-mass limit of star formation.

Additional Information

© 2011 The American Astronomical Society. Received 2011 May 31; accepted 2011 August 22; published 2011 November 22. This paper represents the culmination of a year's worth of effort following up the first batch of brown dwarf candidates identified by WISE. There are many hundreds more candidates still being scrutinized, and there are still areas of sky not yet searched. It is therefore clear that these first hundred brown dwarf discoveries are harbingers of a much larger trove of brown dwarfs yet to be uncovered by WISE. Not only is the WISE data archive uniquely suited to finding even colder objects than the current batch of early-Y dwarfs, the all-sky and multiepoch nature of the mission will enable many other brown dwarf studies—the search for the lowest mass objects in nearby moving groups, hunting for low-metallicity objects via their high proper motions, etc.—that are well beyond the scope of the photometric search presented here. This publication makes use of data products from the Widefield Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. We acknowledge fruitful discussions with Tim Conrow, Roc Cutri, and Frank Masci, and acknowledge assistance with Magellan/FIRE observations by Emily Bowsher. This publication also makes use of data products from 2MASS, SDSS, and UKIDSS. 2MASS is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. SDSS is funded by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England. UKIDSS uses the Wide Field Camera at the United Kingdom Infrared Telescope atop Mauna Kea, Hawai'i. We are grateful for the efforts of the instrument, calibration, and pipeline teams that have made the UKIDSS data possible. We acknowledge use of the DSS, which were produced at the Space Telescope Science Institute under U.S. Government grant NAG W-2166. The images of these surveys are based on photographic data obtained using the Oschin Schmidt Telescope on Palomar Mountain and the UK Schmidt Telescope. This research has made use of the NASA/IPAC Infrared Science Archive (IRSA), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Our research has benefited from the M, L, and T dwarf compendium housed at DwarfArchives.org, whose server was funded by a NASA Small Research Grant, administered by the American Astronomical Society. We are also indebted to the SIMBAD database, operated at CDS, Strasbourg, France. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. Support for this work was provided by NASA through an award issued to program 70062 by JPL/Caltech. This work is also based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program 12330. Support for program 12330 was provided by NASA through a grant from the Space Telescope Science Institute. Some of the spectroscopic data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. In acknowledgement of our observing time at Keck and the IRTF, we further wish to recognize the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawai'ian community. We are most fortunate to have the opportunity to conduct observations from this mountain. We acknowledge use of 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 loaned from the University of Virginia, and the continued support of the SAO and UC Berkeley. The PAIRITEL project is supported by NASA Grant NNX10AI28G. We thank Dan Starr, Cullen Blake, Adam Morgan, Adam Miller, and Chris Klein for their assistance. This paper also includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. Portions of our Magellan telescope time were granted by the National Optical Astronomy Observatory (NOAO; Proposal ID 2010B-0184), through the Telescope System Instrumentation Program (TSIP). TSIP is funded by NOAO, which is operated by the Association of Universities for Research in Astronomy under cooperative agreement with the National Science Foundation. We thank Alan Tokunaga for granting director's discretionary time with IRTF/SpeX for some of the observations presented herein.

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