September 2008 • 2008AJ....136.1290R
Abstract • Using data from the 2 Micron All Sky Survey All-Sky Point Source Catalogue, we have extended our census of nearby ultracool dwarfs to cover the full celestial sphere above Galactic latitude of 15°. Starting with an initial catalog of 2,139,484 sources, we have winnowed the sample to 467 candidate late-type M or L dwarfs within 20 pc of the Sun. Fifty-four of those sources already have spectroscopic observations confirming them as late-type dwarfs. We present optical spectroscopy of 376 of the remaining 413 sources, and identify 44 as ultracool dwarfs with spectroscopic distances less than 20 pc. Twenty-five of the 37 sources that lack optical data have near-infrared spectroscopy. Combining the present sample with our previous results and data from the literature, we catalog 94 L dwarf systems within 20 pc. We discuss the distribution of activity, as measured by Hα emission, in this volume-limited sample. We have coupled the present ultracool catalog with data for stars in the northern 8 pc sample and recent (incomplete) statistics for T dwarfs to provide a snapshot of the current 20 pc census as a function of spectral type.