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A very cool brown dwarf in UKIDSS DR1

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Title: A very cool brown dwarf in UKIDSS DR1
Authors: Warren, SJ
Mortlock, DJ
Leggett, SK
Pinfield, DJ
Homeier, D
Dye, S
Jameson, RF
Lodieu, N
Lucas, PW
Adamson, AJ
Allard, F
Barrado y Navascues, D
Casali, M
Chiu, K
Hambly, NC
Hewett, PC
Hirst, P
Irwin, MJ
Lawrence, A
Liu, MC
Martin, EL
Smart, RL
Valdivielso, L
Venemans, BP
Item Type: Journal Article
Abstract: We report the discovery of a very cool brown dwarf, ULAS J003402.77−005206.7 (ULAS J0034−00), identified in the UKIRT Infrared Deep Sky Survey First Data Release. We provide optical, near‐infrared, and mid‐infrared photometry of the source, and two near‐infrared spectra. Comparing the spectral energy distribution of ULAS J0034−00 to that of the T8 brown dwarf 2MASS J04151954−0935066 (2MASS J0415−09), the latest type and coolest well‐studied brown dwarf to date, with effective temperature Teff∼ 750 K, we find evidence that ULAS J0034−00 is significantly cooler. First, the measured values of the near‐infrared absorption spectral indices imply a later classification, of T8.5. Secondly, the H−[4.49] colour provides an empirical estimate of the effective temperature of 540 < Teff < 660 K (± 2σ range). Thirdly, the J‐ and H‐band peaks are somewhat narrower in ULAS J0034−00, and detailed comparison against spectral models calibrated to 2MASS J0415−09 yields an estimated temperature lower by 60 < ΔTeff < 120 K relative to 2MASS J0415−09 i.e. 630 < Teff < 690 K (± 2σ), and lower gravity or higher metallicity according to the degenerate combination −0.5 < Δ(log  g− 2[m/H]) < −0.25 (± 2σ). Combining these estimates, and considering systematics, it is likely the temperature lies in the range 600 < Teff < 700 K. Measurement of the parallax will allow an additional check of the inferred low temperature. Despite the low inferred Teff we find no evidence for strong absorption by NH3 over the wavelength range 1.51–1.56 μm. Evolutionary models imply that the mass and age are in the ranges 15–36 MJup and 0.5–8 Gyr, respectively. The measured proper motion, of 0.37 ± 0.07 arcsec yr−1, combined with the photometrically estimated distance of 14–22 pc, implies a tangential velocity of ∼30 km s−1, a value consistent with expectation for the inferred age. ULAS J0034−00 is significantly bluer than 2MASS J0415−09 in Y−J, so future searches should allow for the possibility that cooler T dwarfs are bluer still.
Issue Date: 11-Nov-2007
Date of Acceptance: 7-Aug-2007
URI: http://hdl.handle.net/10044/1/73480
DOI: https://doi.org/10.1111/j.1365-2966.2007.12348.x
ISSN: 0035-8711
Publisher: Oxford University Press (OUP)
Start Page: 1400
End Page: 1412
Journal / Book Title: Monthly Notices of the Royal Astronomical Society
Volume: 381
Issue: 4
Copyright Statement: © 2007 Oxford University Press. This is a pre-copy-editing, author-produced version of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The definitive publisher-authenticated version S. J. Warren, D. J. Mortlock, S. K. Leggett, D. J. Pinfield, D. Homeier, S. Dye, R. F. Jameson, N. Lodieu, P. W. Lucas, A. J. Adamson, F. Allard, D. Barrado y Navascués, M. Casali, K. Chiu, N. C. Hambly, P. C. Hewett, P. Hirst, M. J. Irwin, A. Lawrence, M. C. Liu, E. L. Martín, R. L. Smart, L. Valdivielso, B. P. Venemans, A very cool brown dwarf in UKIDSS DR1, Monthly Notices of the Royal Astronomical Society, Volume 381, Issue 4, November 2007, Pages 1400–1412, https://doi.org/10.1111/j.1365-2966.2007.12348.x is available online at: https://doi.org/10.1111/j.1365-2966.2007.12348.x.
Keywords: Science & Technology
Physical Sciences
Astronomy & Astrophysics
surveys
stars
low-mass
brown dwarfs
SPITZER-SPACE-TELESCOPE
DIGITAL SKY SURVEY
EARLY DATA RELEASE
EFFECTIVE TEMPERATURE CALIBRATIONS
BAND PHOTOMETRIC COLORS
INFRARED ARRAY CAMERA
EXOPLANET HOST STAR
LATE-TYPE GIANTS
T-DWARFS
SPECTRAL CLASSIFICATION
astro-ph
astro-ph
Astronomy & Astrophysics
0201 Astronomical and Space Sciences
Publication Status: Published
Conference Place: UK
Online Publication Date: 2007-10-17
Appears in Collections:Physics
Astrophysics
Faculty of Natural Sciences