S. K. Leggett, D. Saumon, M. S. Marley, K. Lodders, J. Canty, P. Lucas, R. L. Smart, C. G. Tinney, D. Homeier, F. Allard, Ben Burningham, A. Day-Jones, B. Fegley, Miki Ishii, H. R. A. Jones, F. Marocco, D. J. Pinfield, M. Tamura
We present i and z photometry for 25 T dwarfs and one 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 um and 2.8-4.2 um 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 the 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-2 4.5 um 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.
View original:
http://arxiv.org/abs/1201.2973
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