The Properties of the 500 K Dwarf UGPS J072227.51-054031.2 and a Study of the Far-red Flux of Cold Brown Dwarfs

April 2012 • 2012ApJ...748...74L

Authors • Leggett, S. K. • Saumon, D. • Marley, M. S. • Lodders, K. • Canty, J. • Lucas, P. • Smart, R. L. • Tinney, C. G. • Homeier, D. • Allard, F. • Burningham, Ben • Day-Jones, A. • Fegley, B. • Ishii, Miki • Jones, H. R. A. • Marocco, F. • Pinfield, D. J. • Tamura, M.

Abstract • We present i and z photometry for 25 T dwarfs and 1 L dwarf. Combined with published photometry, the data show that the i - z, z - Y, and z - J colors of T dwarfs are very red, and continue to increase through to the late-type T dwarfs, with a hint of a saturation for the latest types with T _eff ≈ 600 K. We present new 0.7-1.0 μm and 2.8-4.2 μm spectra for the very late type T dwarf UGPS J072227.51-054031.2, as well as improved astrometry for this dwarf. Examination of the spectral energy distribution using new and published data, with Saumon & Marley models, shows that the dwarf has T _eff = 505 ± 10 K, a mass of 3-11 M _Jupiter, and an age between 60 Myr and 1 Gyr. This young age is consistent with the thin disk kinematics of the dwarf. The mass range overlaps with that usually considered to be planetary, despite this being an unbound object discovered in the field near the Sun. This apparently young rapid rotator is also undergoing vigorous atmospheric mixing, as determined by the IRAC and WISE 4.5 μm photometry and the Saumon & Marley models. The optical spectrum for this 500 K object shows clearly detected lines of the neutral alkalis Cs and Rb, which are emitted from deep atmospheric layers with temperatures of 900-1200 K.

Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Science and Technology Facilities Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência e Tecnologia (Brazil), and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina); also based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan; and also based on observations made at the UK Infrared Telescope, which operated by the Joint Astronomy Centre on behalf of the Science and Technology Facilities Council of the UK.

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Federico Marocco

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