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Fifteen new T dwarfs discovered in the UKIDSS Large Area Survey


Pinfield, DJ and Burningham, B and Tamura, M and Leggett, SK and Lodieu, N and Lucas, PW and Mortlock, DJ and Warren, SJ and Homier, D and Ishii, M and Deacon, NR and McMahon, RG and Hewett, PC and Zapatero Osori, MR and Martin, EL and Jones, HRA and Venemans, BP and Day-Jones, AC and Dobbie, PD and Folkes, SL and Dye, S and Allard, F and Baraffe, I and Barrado y Navascues, D and Casewell, SL and Chiu, K and Chabrier, G and Clarke, F and Hodgkin, ST and Magazzu, A and McCaughrean, MJ and Nakajima, T and Pavlenko, Y and Tinney, CG, Fifteen new T dwarfs discovered in the UKIDSS Large Area Survey, Monthly Notices of the Royal Astronomical Society, 390, (1) pp. 304-322. ISSN 0035-8711 (2008) [Refereed Article]

Copyright Statement

Copyright 2008 The Authors. Journal compilation 2008 RAS

DOI: doi:10.1111/j.1365-2966.2008.13729.x


We present the discovery of 15 new T2.5T7.5 dwarfs (with estimated distances ∼2493 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 T2.5T4.5, five have spectral types of T5T5.5, one is a T6.5p and two are T77.5. 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 Y − J with decreasing effective temperature, and some interesting colour changes in J − H and z − J (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.

Item Details

Item Type:Refereed Article
Keywords:techniques: photometric; techniques: spectroscopic; surveys; stars: low-mass, brown dwarfs; infrared: stars
Research Division:Physical Sciences
Research Group:Astronomical sciences
Research Field:Stellar astronomy and planetary systems
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the physical sciences
UTAS Author:Dobbie, PD (Dr Paul Dobbie)
ID Code:81038
Year Published:2008
Web of Science® Times Cited:84
Deposited By:Mathematics and Physics
Deposited On:2012-11-21
Last Modified:2013-06-27

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