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 theKeck Laser Guide Star AO system. We resolved Allers et al. (2006)'s #11 (Oph16222-2405) and #16 (Oph 16233-2402) into binary systems. The #11 object isresolved into a 243 AU binary, the widest known for a very low mass (VLM)binary. The binary nature of #11 was discovered first by Allers (2005) andindependently here during which we obtained the first spatially resolved R~2000near-infrared (J & 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/Lsun)=-2.77+/-0.10 and -2.96+/-0.10), and temperatures(Teff=2375+/-175 and 2175+/-175 K). We find self-consistent DUSTY evolutionarymodel (Chabrier et al. 2000) masses of 17+4-5 MJup and 14+6-5 MJup, for 11A and11B respectively. Our masses are higher than those previously reported (13-15MJup and 7-8 MJup) by Jayawardhana & Ivanov (2006b). Hence, we find the systemis unlikely a ``planetary mass binary'', (in agreement with Luhman et al. 2007)but it has the second lowest mass and lowest binding energy of any knownbinary. Oph #11 and Oph #16 belong to a newly recognized population of wide(>100 AU), young (<10 Myr), roughly equal mass, VLM stellar and brown dwarfbinaries. We deduce that ~6+/-3% of young (<10 Myr) VLM objects are in suchwide systems. However, only 0.3+/-0.1% of old field VLM objects are found insuch wide systems. Thus, young, wide, VLM binary populations may beevaporating, due to stellar encounters in their natal clusters, leading to afield population depleted in wide VLM systems.Comment: Accepted version V2. Now 13 pages longer (45 total) due to a new discussion of the stability of the wide brown dwarf binary population, new summary Figure 17 now included, Astrophysical Journal 2007 in pres