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

December 2011 • 2011ApJ...743...50C

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

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IPAC Authors
(alphabetical)

Chris Gelino

Associate Scientist

Davy Kirkpatrick

Senior Scientist