Journal
ASTROPHYSICAL JOURNAL
Volume 743, Issue 1, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/743/1/50
Keywords
brown dwarfs; infrared: stars; stars: individual (UGPS J072227.51-054031.2, WISEPC J014807.25, 720258.8, WISEP J041022.71+150248.5, WISEPC J140518.40+553421.5, WISEP J154151.65225025.2, WISEP J173835.52+273258.9, WISEP J182831.08+265037.8, WISEPC J205628.90+145953.3); stars: low-mass
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Funding
- NASA
- National Aeronautics and Space Administration
- National Science Foundation
- Alfred P. Sloan Foundation
- U.S. Department of Energy
- Japanese Monbukagakusho
- Max Planck Society
- Higher Education Funding Council for England
- W. M. Keck Foundation
- Harvard University Milton Fund
- University of Virginia
- SAO
- University of California, Berkeley
- NOAO through the Telescope System Instrumentation Program (TSIP) [2010B-0184]
- National Aeronautics and Space Administration [NNG06GH50G]
- Chris and Warren Hellman Fellowship
- Division Of Astronomical Sciences
- Direct For Mathematical & Physical Scien [1109115, 0908920] Funding Source: National Science Foundation
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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 H2O and CH4 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 lambda, 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.
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