Eight new T4.5-T7.5 dwarfs discovered in the UKIDSS Large Area Survey Data Release 1

Abstract

We present eight new T4.5-T7.5 dwarfs identified in the UKIRT Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS) Data Release 1 (DR1). In addition we have recovered the T4.5 dwarf SDSS J020742.91+000056.2 and the T8.5 dwarf ULAS J003402.77-005206.7. Photometric candidates were picked up in two-colour diagrams over 190 square degrees (DR1) and selected in at least two filters. All candidates exhibit near-infrared spectra with strong methane and water absorption bands characteristic of T dwarfs and the derived spectral types follow the unified scheme of Burgasser et al. (2006). We have found 6 new T4.5-T5.5 dwarfs, one T7 dwarf, one T7.5 dwarf, and recovered a T4.5 dwarf and a T8.5 dwarf. We provide distance estimates which lie in the 15-85 pc range; the T7.5 and T8.5 dwarfs are probably within 25 pc of the Sun. We conclude with a discussion of the number of T dwarfs expected after completion of the LAS, comparing these initial results to theoretical simulations.

10 pages, 4 figures, 3 tables, 1 appendix, accepted for publication in MNRAS, Figure 2 is a low-resolution version

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