Discovery of an L4$\beta$ Candidate Member of Argus in the Planetary Mass Regime: WISE J231921.92+764544.4

Abstract

We present the discovery of a young L dwarf, WISE J231921.92+764544.4, identified by comparing the Wide-field Infrared Survey Explorer (WISE) All-Sky Catalog to the Two Micron All Sky Survey (2MASS). A medium-resolution optical spectrum provides a spectral type of L4$\beta$, with a photometric distance estimate of 26.1$\pm$4.4 pc. The red WISE $W1-W2$ color provides additional evidence of youth, while the 2MASS $J-K_{\mathrm{s}}$ color does not. WISE J231921.92+764544.4 is a candidate member of the young moving group Argus, with the space motion and position of WISE J231921.92+764544.4 giving a probability of 79% membership in Argus and a probability of 21% as a field object, based on BANYAN II. WISE J231921.92+764544.4 has a mass of 12.1$\pm$0.4 M${}_{\mathrm{Jup}}$ based on membership in Argus, within the planetary mass regime.

19 pages, 6 figures, accepted for publication in The Astrophysical Journal (ApJ)