Identifying ultra-cool dwarfs at low Galactic latitudes : a southern candidate catalogue

Abstract

We present an ultra-cool dwarf (UCD) catalogue compiled from low southern Galactic latitudes and mid-plane, from a cross-correlation of the Two Micron All-Sky Survey (2MASS) and the SuperCOSMOS survey. The catalogue contains 246 members identified from 5042 deg(2) within 220 degrees = 10). This method does not require candidates to have optical detections for catalogue inclusion. An optimal set of optical/near-IR and reduced proper-motion selection criteria have been defined that includes: an R-F and I-N photometric surface gravity test; a dual R-F-band variability check and an additional photometric classification scheme to selectively limit numbers of potential contaminants in regions of severe overcrowding. We identify four candidates as possible companions to nearby Hipparcos stars-observations are needed to identify these as potential benchmark UCD companions. We also identify 12 UCDs within a possible distance 20 pc, three are previously unknown of which two are estimated within 10 pc, complementing the nearby volume-limited census of UCDs. An analysis of the catalogue spatial completeness provides estimates for distance completeness over three UCD M-J ranges, while Monte Carlo simulations provide an estimate of catalogue areal completeness at the 75 per cent level. We estimate a UCD space density of rho((total)) = (6.41 +/- 3.01) x 10(-3) pc(-3) over the range of 10.5