Journal Article

47 new T dwarfs from the UKIDSS Large Area Survey

Ben Burningham, D. J. Pinfield, P. W. Lucas, S. K. Leggett, N. R. Deacon, M. Tamura, C. G. Tinney, N. Lodieu, Z. H. Zhang, N. Huelamo, H. R. A. Jones, D. N. Murray, D. J. Mortlock, M. Patel, D. Barrado y Navascués, M. R. Zapatero Osorio, M. Ishii, M. Kuzuhara and R. L. Smart

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 406, issue 3, pages 1885-1906
Published in print August 2010 | ISSN: 0035-8711
Published online August 2010 | e-ISSN: 1365-2966 | DOI:
47 new T dwarfs from the UKIDSS Large Area Survey

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We report the discovery of 47 new T dwarfs in the Fourth Data Release (DR4) from the Large Area Survey (LAS) of the United Kingdom Infrared Telescope (UKIRT) Infrared Deep Sky Survey with spectral types ranging from T0 to T8.5. These bring the total sample of LAS T dwarfs to 80 as of DR4. In assigning spectral types to our objects we have identified eight new spectrally peculiar objects, and divide seven of them into two classes. H2O-H-early have a H2O-H index that differs with the H2O-J index by at least two subtypes. CH4-J-early have a CH4-J index that disagrees with the H20-J index by at least two subtypes. We have ruled out binarity as a sole explanation for both types of peculiarity, and suggest that they may represent hitherto unrecognized tracers of composition and/or gravity. Clear trends in z′(AB) −J and YJ are apparent for our sample, consistent with weakening absorption in the red wing of the K i line at 0.77 μm with decreasing effective temperature. We have used our sample to estimate space densities for T6–T9 dwarfs. By comparing our sample to Monte Carlo simulations of field T dwarfs for various mass functions of the form ψ(M) ∝ M−α pc−3 M−1, we have placed weak constraints on the form of the field mass function. Our analysis suggests that the substellar mass function is declining at lower masses, with negative values of α preferred. This is at odds with results for young clusters that have been generally found to have α > 0.

Keywords: surveys; brown dwarfs; stars: low-mass

Journal Article.  11312 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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