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Title:
The Physical Properties of Four ~600 K T Dwarfs
Authors:
Leggett, S. K.; Cushing, Michael C.; Saumon, D.; Marley, M. S.; Roellig, T. L.; Warren, S. J.; Burningham, Ben; Jones, H. R. A.; Kirkpatrick, J. D.; Lodieu, N.; Lucas, P. W.; Mainzer, A. K.; Martín, E. L.; McCaughrean, M. J.; Pinfield, D. J.; Sloan, G. C.; Smart, R. L.; Tamura, M.; Van Cleve, J.
Affiliation:
AA(Gemini Observatory, 670 N. A'hoku Place, Hilo, HI 96720, USA ), AB(Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA), AC(Los Alamos National Laboratory, P.O. Box 1663, MS F663, Los Alamos, NM 87545, USA), AD(NASA Ames Research Center, Mail Stop 245-3, Moffett Field, CA 94035, USA), AE(NASA Ames Research Center, Mail Stop 245-3, Moffett Field, CA 94035, USA), AF(Imperial College London, Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK), AG(Centre for Astrophysics Research, Science and Technology Research Institute, University of Hertfordshire, Hatfield AL10 9AB, UK), AH(Centre for Astrophysics Research, Science and Technology Research Institute, University of Hertfordshire, Hatfield AL10 9AB, UK), AI(IPAC, California Institute of Technology, Mail Code 100-22, 770 South Wilson Avenue, Pasadena, CA 91125, USA), AJ(Instituto de Astrofsica de Canarias, 38200 La Laguna, Spain), AK(Centre for Astrophysics Research, Science and Technology Research Institute, University of Hertfordshire, Hatfield AL10 9AB, UK), AL(Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA), AM(Instituto de Astrofsica de Canarias, 38200 La Laguna, Spain; University of Central Florida, Physics Department, PO Box 162385, Orlando, FL 32816, USA), AN(School of Physics, University of Exeter, Stocker Road, Exeter, Devon EX4 4QL, UK), AO(Centre for Astrophysics Research, Science and Technology Research Institute, University of Hertfordshire, Hatfield AL10 9AB, UK), AP(Astronomy Department, Cornell University, Ithaca, NY 14853, USA), AQ(INAF-Osservatorio Astronomico di Torino, Strada Osservatorio 20, 10025 Pino Torinese, TO, Italy), AR(National Astronomical Observatory, Mitaka, Tokyo 181-8588, Japan), AS(Ball Aerospace and Technologies Corp., Boulder, CO 80301, USA)
Publication:
The Astrophysical Journal, Volume 695, Issue 2, pp. 1517-1526 (2009). (ApJ Homepage)
Publication Date:
04/2009
Origin:
IOP
Astronomy Keywords:
stars: atmospheres, stars: individual: ULAS J003402.77--005206.7 ULAS J133553.45+113005.2 2MASS J09393548--2448279 CFBD J005910.82--011401.3, stars: low-mass, brown dwarfs
DOI:
10.1088/0004-637X/695/2/1517
Bibliographic Code:
2009ApJ...695.1517L

Abstract

We present Spitzer 7.6-14.5 mum spectra of ULAS J003402.77-005206.7 and ULAS J133553.45+113005.2, two T9 dwarfs with the latest spectral types currently known. We fit synthetic spectra and photometry to the near- through mid-infrared energy distributions of these dwarfs and that of the T8 dwarf 2MASS J09393548-2448279. We also analyze near-infrared data for another T9, CFBD J005910.82-011401.3. We find that the ratio of the mid- to near-infrared fluxes is very sensitive to effective temperature at these low temperatures, and that the 2.2 mum and 4.5 mum fluxes are sensitive to metallicity and gravity; increasing gravity has a similar effect to decreasing metallicity, and vice versa, and there is a degeneracy between these parameters. The 4.5 mum and 10 mum fluxes are also sensitive to vertical transport of gas through the atmosphere, which we find to be significant for these dwarfs. The full near- through mid-infrared spectral energy distribution allows us to constrain the effective temperature (K)/gravity (ms-2)/metallicity ([m/H] dex) of ULAS J0034-00 and ULAS J1335+11 to 550-600/100-300/0.0-0.3 and 500-550/100-300/0.0-0.3, respectively. These fits imply low masses and young ages for the dwarfs of 5-20 M Jupiter and 0.1-2 Gyr. The fits to 2MASS J0939-24 are in good agreement with the measured distance, the observational data, and the earlier T8 near-infrared spectral type if it is a slightly metal-poor 4-10 Gyr old system consisting of a 500 K and 700 K, ~25 M Jupiter and ~40 M Jupiter, pair, although it is also possible that it is an identical pair of 600 K, 30 M Jupiter, dwarfs. As no mid-infrared data are available for CFBD J0059-01 its properties are less well constrained; nevertheless it appears to be a 550-600 K dwarf with g= 300-2000 ms-2 and [m/H] = 0-0.3 dex. These properties correspond to mass and age ranges of 10-50 M Jupiter and 0.5-10 Gyr for this dwarf.
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