A Candidate Wide Brown Dwarf Binary in the Argus Association: 2MASS J14504216–7841413 and 2MASS J14504113–7841383

Abstract

Widely-separated (≳100 au) multiples are rare among the lowest mass stars and brown dwarfs (Caballero 2007; Kraus & Hillenbrand 2009), and often (but not exclusively) associated with young (≾100 Myr), nearby stellar associations (e.g., Close et al. 2007). We report the discovery of a wide, very low mass, and potentially young binary, 2MASS J14504216–7841413 and 2MASS J14504113–7841383 (hereafter 2MASS J1450–7841AB). The primary was initially identified in the DENIS (Epchtein et al. 1997) and 2MASS (Skrutskie et al. 2006) surveys as a candidate late-M dwarf based on its red optical/infrared colors (DENIS I = 18.03 ± 0.16, I − J = 3.32 ± 0.19, 2MASS J = 14.71 ± 0.06, J – K_s = 1.38 ± 0.08). A faint red companion, 2MASS J14504113–7841383, is present in the 2MASS Point Source Catalog (J = 15.64 ± 0.09, J – K_s = 1.28 ± 0.14) separated by 4.”23 ± 0.”11 at position angle 314°. We observed 2MASS J1450–7841AB with the Low Dispersion Survey Spectrograph 3 (LDSS-3; Allington-Smith et al. 1994) on the Magellan 6.5 m Clay Telescope on 2007 May 9 (UT). The system was resolved in i- and z-band imaging data at an identical separation (4.”28 ± 0.”14 at 314°; Figure 1) as 2MASS, with Δi = 1.03 ± 0.05 and Δz = 1.01 ± 0.05. Combining astrometry from 2MASS and LDSS-3, we measure identical proper motions of (μ_α cos δ, μδ) = (22 ± 32, −59 ± 34) mas/yr for 2MASS J1450–7841A and (−12 ± 23, −4 ± 23) mas/yr for 2MASS J1450–7841B.