Meeting the Cool Neighbors X: Ultracool dwarfs from the 2MASS All-Sky Data Release

TL;DR

This paper expands the census of nearby ultracool dwarfs using 2MASS data, confirming 94 within 20 parsecs, and analyzes their distribution and activity, providing a comprehensive snapshot of the local ultracool dwarf population.

Contribution

It presents a complete all-sky survey of ultracool dwarfs within 20 parsecs, including new spectroscopic confirmations and a detailed analysis of their distribution and activity.

Findings

94 L dwarf systems within 20 parsecs identified

Spectroscopic confirmation of 44 ultracool dwarfs

Distribution of activity measured by H-alpha emission

Abstract

Using data from the 2MASS All-Sky Point Source Catalogue, we have extended our census of nearby ultracool dwarfs to cover the full celestial sphere above Galactic latitute 15 degrees. Starting with an initial catalogue of 2,139,484 sources, we have winnowed the sample to 467 candidate late-type M or L dwarfs within 20 parsecs 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 parsecs. 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 catalogue 94 L dwarf systems within 20 parsecs. We discuss the distribution of activity, as measured by H-alpha emission, in this volume-limited sample. We have coupled the present ultracool catalogue with data for stars in the northern 8-parsec sample and recent (incomplete) statistics for T dwarfs to provide a snapshot of the current 20-parsec census as a function of spectral type.