Meeting the Cool Neighbours, VI: A search for nearby ultracool dwarfs in the Galactic Plane

Abstract

Surveys for nearby low-luminosity dwarfs tend to avoid the crowded regions of the Galactic Plane. We have devised near-infrared colour-magnitude and colour-colour selection criteria designed to identify late-type M and early-type L dwarfs within 12 parsecs of the Sun. We use those criteria to search for candidates within the regions of the Galactic Plane (|b| < 10^o) covered by the Second Incremental Release of data from the Two-Micron All Sky Survey. Detailed inspection of the available photographic images of the resulting 1299 candidates confirms only two as ultracool dwarfs. Both are known proper motion stars, identified in the recent survey by Lepine et al (2002). Despite the low numbers, the inferred surface density is consistent with comparable surveys at higher latitudes. We discuss the implications for the luminosity function, and consider means of improving the efficiency and scope of photometric surveys in the Plane.