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

TL;DR

This paper reports the discovery of eight new T-type brown dwarfs in the UKIDSS survey, expanding the known population and providing spectral and distance estimates, with implications for understanding the substellar census.

Contribution

First identification of eight new T4.5-T7.5 dwarfs in the UKIDSS LAS, including recovered known objects, with spectral classification and distance estimation.

Findings

Six new T4.5-T5.5 dwarfs discovered

One T7 dwarf identified

One T7.5 dwarf identified

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.