The wide brown dwarf binary Oph 1622-2405 and discovery of a wide, low-mass binary in Ophiuchus (Oph 1623-2402): A new class of young evaporating wide binaries?

We imaged five objects near the star-forming clouds of Ophiuchus with the Keck Laser Guide Star AO system. We resolved sources 11 ( Oph 16222 - 2405) and 16 ( Oph 16233 - 2402) from Allers and coworkers into binary systems. Source 11 is resolved into a 243 AU binary, the widest known for a very low mass (VLM) binary. The binary nature of source 11 was discovered first by Allers and independently here, during which we obtained the first spatially resolved R - 2000 near-infrared ( J and K) spectra, mid-IR photometry, and orbital motion estimates. We estimate for 11A and 11B gravities ( log g > 3.75), ages ( 5 +/- 2 Myr), luminosities [ log ( L/ L circle dot )= -2: 77 +/- 0.10 and -2. 96 +/- 0.10], and temperatures ( T-eff = 2375 +/- 175 K and 2175 +/- 175 K). We find self-consistent DUSTY evolutionary model ( Chabrier and coworkers) masses of 17(-5)(+4) 5 MJ and 14(-5)(+6) 5 MJ, for 11A and 11B, respectively. Our masses are higher than those previously reported ( 13-15 MJ and 7-8 MJ) by Jayawardhana & Ivanov. Hence, we find that the system is unlikely a planetary mass binary,'' as do Luhman and coworkers, but it has the second lowest mass and lowest binding energy of any known binary. Oph 11 and Oph 16 belong to a newly recognized population of wide ( greater than or similar to 100 AU), young (< 10 Myr), roughly equal mass, VLM stellar and brown dwarf binaries. We deduce that - 6% +/- 3% of young (< 10 Myr) VLM objects are in such wide systems. However, only 0. 3% +/- 0.1% of old field VLM objects are found in such wide systems. Thus, young, wide, VLM binary populations may be evaporating, due to stellar encounters in their natal clusters, leading to a field population depleted in wide VLM systems.