1 um Excess Sources in the UKIDSS - I. Three T Dwarfs in the SDSS Southern Equatorial Stripe

TL;DR

This paper reports the discovery and characterization of three distant early-T brown dwarfs in the SDSS southern stripe, including spectral analysis, distance estimation, proper motion measurement, and brightness stability assessment.

Contribution

It presents the identification and detailed analysis of three new T dwarfs, including their spectra, distances, motions, and brightness stability, expanding knowledge of distant brown dwarfs.

Findings

Discovered three new early-T dwarfs at 50-110 pc distance.

Measured significant proper motions indicating high transverse velocities.

Found no long-term brightness variations above 0.1 mag.

Abstract

We report the discovery of two field brown dwarfs, ULAS J0128-0041 and ULAS J0321+0051, and the rediscovery of ULAS J0226+0051 (IfA 0230-Z1), in the Sloan Digital Sky Survey (SDSS) southern equatorial stripe. They are found in the course of our follow-up observation program of 1 um excess sources in the United Kingdom Infrared Telescope Infrared Deep Sky Survey. The Gemini Multi-Object Spectrographs spectra at red optical wavelengths (6500-10500 A) are presented, which reveal that they are early-T dwarfs. The classification is also supported by their optical to near-infrared colors. It is noted that ULAS J0321+0051 is one of the faintest currently known T dwarfs. The estimated distances to the three objects are 50-110 pc, thus they are among the most distant field T dwarfs known. Dense temporal coverage of the target fields achieved by the SDSS-II Supernova Survey allows us to perform a simple time-series analysis, which leads to the finding of significant proper motions of 150-290 mas/yr or the transverse velocities of 40-100 km/s for ULAS J0128-0041 and ULAS J0226+0051. We also find that there are no detectable, long-term (a-few-year) brightness variations above a few times 0.1 mag for the two brown dwarfs.