Physical parameters of two very cool T dwarfs

D. Saumon, M. S. Marley, S. K. Leggett, T. R. Geballe, D. Stephens, D. A. Golimowski, M. C. Cushing, X. Fan, J. T. Rayner, K. Lodders, R. S. Freedman

Research output: Contribution to journalArticle

75 Scopus citations

Abstract

We present new infrared spectra of the T8 brown dwarf 2MASS J04151954-0935066: 2.9-4.1 μm spectra obtained with the Infrared Camera and Spectrograph on the Subaru Telescope, and 5.2-14.5 μm spectra obtained with the Infrared Spectrograph on the Spitzer Space Telescope. We use these data and models to determine an accurate bolometric luminosity of log L bol/L = -5.67 and to constrain the effective temperature, gravity, mass, and age to 725-775 K, log g = 5.00-5.37, M = 33-58 MJup, and age = 3-10 Gyr. We perform the same analysis using published 0.6-15 μm spectra for the T7.5 dwarf 2MASSJ12171110-0311131, for which we find a metal-rich composition ([Fe/H] ∼ 0.3), and log L bol/L = -5.31, Teff = 850-950 K, log g = 4.80-5.42, M = 25-66 MJup, and age = 1-10 Gyr. These luminosities and effective temperatures straddle those determined with the same method and models for Gl 570D by Saumon et al. and make 2MASS J04151954-0935066 the coolest and least luminous T dwarf with well-determined properties. We find that synthetic spectra generated by the models reproduce the observed red through mid-infrared spectra of 2MASS J04151954-0935066 and 2MASS J12171110-0311131 very well, except for known discrepancies that are most likely due to the incomplete CH4 opacities. Both objects show evidence of departures from strict chemical equilibrium, and we discuss this result in the context of other late T dwarfs in which disequilibrium phenomena have been observed.

Original languageEnglish (US)
Pages (from-to)1136-1149
Number of pages14
JournalAstrophysical Journal
Volume656
Issue number2 I
DOIs
StatePublished - Feb 20 2007

Keywords

  • Stars: individual (2MASS J04151954-0935066, 2MASS J12171110-0311131, G1 570D)
  • Stars: low-mass, brown dwarfs

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Saumon, D., Marley, M. S., Leggett, S. K., Geballe, T. R., Stephens, D., Golimowski, D. A., Cushing, M. C., Fan, X., Rayner, J. T., Lodders, K., & Freedman, R. S. (2007). Physical parameters of two very cool T dwarfs. Astrophysical Journal, 656(2 I), 1136-1149. https://doi.org/10.1086/510557