The Discovery of Y Dwarfs using Data from the Wide-field Infrared Survey Explorer (WISE)

Creators: Cushing, Michael C.; Kirkpatrick, J. Davy; Gelino, Christopher R.; Griffith, Roger L.; Skrutskie, Michael F.; Mainzer, A.; Marsh, Kenneth A.; Beichman, Charles A.; Burgasser, Adam J.; Prato, Lisa A.; Simcoe, Robert A.; Marley, Mark S.; Saumon, D.; Freedman, Richard S.; Eisenhardt, Peter R.; Wright, Edward L.

Abstract

We present the discovery of seven ultracool brown dwarfs identified with the Wide-field Infrared Survey Explorer (WISE). Near-infrared spectroscopy reveals deep absorption bands of H_(2)O and CH_4 that indicate all seven of the brown dwarfs have spectral types later than UGPS J072227.51–054031.2, the latest-type T dwarf currently known. The spectrum of WISEP J182831.08+265037.8 is distinct in that the heights of the J- and H-band peaks are approximately equal in units of f λ, so we identify it as the archetypal member of the Y spectral class. The spectra of at least two of the other brown dwarfs exhibit absorption on the blue wing of the H-band peak that we tentatively ascribe to NH3. These spectral morphological changes provide a clear transition between the T dwarfs and the Y dwarfs. In order to produce a smooth near-infrared spectral sequence across the T/Y dwarf transition, we have reclassified UGPS 0722–05 as the T9 spectral standard and tentatively assign WISEP J173835.52+273258.9 as the Y0 spectral standard. In total, six of the seven new brown dwarfs are classified as Y dwarfs: four are classified as Y0, one is classified as Y0 (pec?), and WISEP J1828+2650 is classified as >Y0. We have also compared the spectra to the model atmospheres of Marley and Saumon and infer that the brown dwarfs have effective temperatures ranging from 300 K to 500 K, making them the coldest spectroscopically confirmed brown dwarfs known to date.

Additional Information

© 2011 American Astronomical Society. Received 2011 June 10; accepted 2011 August 2; published 2011 November 22. We thank Tom Jarrett for guidance with the WIRC data reduction, Barry Rothberg, and Norbert Pirzkal for their guidance in reducing the HST/WFC3 data, and Ben Burningham, Sandy Leggett, and Mike Liu for providing digital copies of late-type T dwarf spectra. We also thank Mauricio Martinez, Jorge Araya, and Nidia Morrell for observing support at Magellan. M.S.M. and D.S. acknowledge the support of the NASA ATP program. This publication makes use of data products from the Wide-field Infrared Survey Explorer, the Two Micron All Sky Survey (2MASS), and the Sloan Digital Sky Survey (SDSS). The Wide-field Infrared Survey Explorer 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. 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. 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 also 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 and the SpeX Prism Spectral Libraries, maintained by Adam Burgasser at http://www.browndwarfs.org/spexprism. Data presented herein were obtained at the W. M. Keck Observatory from telescope time allocated to the National Aeronautics and Space Administration through the agency's scientific partnership with the California Institute of Technology and the University of California. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. This paper also includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile and the Peters Automated Infrared Imaging Telescope (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. Magellan telescope time was granted by NOAO (Proposal ID 2010B-0184, P.I. Mainzer), through the Telescope System Instrumentation Program (TSIP). TSIP is funded by NSF. National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA) under cooperative agreement with the National Science Foundation. Partial support for PAIRITEL operations and this work comes from National Aeronautics and Space Administration grant NNG06GH50G. A.J.B. acknowledges support from the Chris and Warren Hellman Fellowship Program. Finally, this research was supported (in part) by an appointment to the NASA Postdoctoral Program at the Jet Propulsion Laboratory, administered by Oak Ridge Associated Universities through a contract with NASA. Facilities: IRTF (SpeX), Hale (WIRC), Magellan:Baade (FIRE, PANIC), Keck:II (NIRC2, NIRSPEC), Spitzer (IRAC), HST (WFC3)

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