The discovery of y dwarfs using data from the wide-field infrared survey explorer (WISE)

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

Research output: Contribution to journalArticlepeer-review

265 Scopus citations


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 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 300K to 500K, making them the coldest spectroscopically confirmed brown dwarfs known to date.

Original languageEnglish (US)
Article number50
JournalAstrophysical Journal
Issue number1
StatePublished - Dec 10 2011
Externally publishedYes


  • brown dwarfs
  • infrared: stars
  • stars: low-mass

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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