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 (United Kingdom Infrared Telescope) Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS) Data Release 1 (DR1). In addition we have recovered the T4.5 dwarf SDSSJ020742.91+000056.2 and the T8.5 dwarf ULASJ003402.77-005206.7. Photometric candidates were picked up in two-colour diagrams over 190deg<SUP>2</SUP> (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.. We have found six 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 15-85pc range; the T7.5 and T8.5 dwarfs are probably within 25pc 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. Based on observations made with the United Kingdom Infrared Telescope, operated by the Joint Astronomy Centre on behalf of the UK Particle Physics and Astronomy Research Council. E-mail: nlodieu@iac.es ‡ Alfred P. Sloan Research Fellow.