Journal Article

Fifteen new T dwarfs discovered in the UKIDSS Large Area Survey

D. J. Pinfield, B. Burningham, M. Tamura, S. K. Leggett, N. Lodieu, P. W. Lucas, D. J. Mortlock, S. J. Warren, D. Homeier, M. Ishii, N. R. Deacon, R. G. McMahon, P. C. Hewett, M. R. Zapatero Osori, E. L. Martin, H. R. A. Jones, B. P. Venemans, A. C. Day-Jones, P. D. Dobbie, S. L. Folkes, S. Dye, F. Allard, I. Baraffe, D. Barrado y Navascués, S. L. Casewell, K. Chiu, G. Chabrier, F. Clarke, S. T. Hodgkin, A. Magazzù, M. J. McCaughrean, T. Nakajima, Y. Pavlenko and C. G. Tinney

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 390, issue 1, pages 304-322
Published in print October 2008 | ISSN: 0035-8711
Published online October 2008 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2008.13729.x
Fifteen new T dwarfs discovered in the UKIDSS Large Area Survey

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We present the discovery of 15 new T2.5–T7.5 dwarfs (with estimated distances ∼24–93 pc), identified in the first three main data releases of the United Kingdom Infrared Telescope (UKIRT) Infrared Deep Sky Survey. This brings the total number of T dwarfs discovered in the Large Area Survey (LAS) (to date) to 28. These discoveries are confirmed by near-infrared spectroscopy, from which we derive spectral types on the unified scheme of Burgasser et al. Seven of the new T dwarfs have spectral types of T2.5–T4.5, five have spectral types of T5–T5.5, one is a T6.5p and two are T7–7.5. We assess spectral morphology and colours to identify T dwarfs in our sample that may have non-typical physical properties (by comparison to solar neighbourhood populations), and find that three of these new T dwarfs may have unusual metallicity, two may have low surface gravity, and one may have high surface gravity. The colours of the full sample of LAS T dwarfs show a possible trend to bluer YJ with decreasing effective temperature, and some interesting colour changes in JH and zJ (deserving further investigation) beyond T8. The LAS T dwarf sample from the first and second main data releases show good evidence for a good level of completion to J= 19. By accounting for the main sources of incompleteness (selection, follow-up and spatial) as well as the effects of unresolved binarity, Malmquist and Eddington bias, we estimate that there are 17 ± 4 ≥ T 4 dwarfs in the J≤ 19 volume of the LAS second data release. This value is most consistent with theoretical predictions if the substellar mass function exponent α (dN/dmm−α) lies between −1.0 and 0. This is consistent with the latest 2-Micron All Sky Survey (2MASS)/Sloan Digital Sky Survey (SDSS) constraint (which is based on lower number statistics) and is significantly lower than the α∼ 1.0 suggested by L dwarf field populations, which is possibly a result of the lower mass range probed by the T dwarf class.

Keywords: techniques: photometric; techniques: spectroscopic; surveys; stars: low-mass, brown dwarfs; infrared: stars

Journal Article.  13451 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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