Multiplicity among Widely Separated Brown Dwarf Companions to Nearby Stars: Gliese 337CD

We present Lick Natural Guide Star Adaptive Optics observations of the L8brown dwarf Gliese 337C, which is resolved for the first time into two closelyseparated (0"53+/-0"03), nearly equal magnitude components with a K_s fluxratio of 0.93+/-0.10. Companionship is inferred from the absence of a 3"6offset source in 2MASS or photographic plate images, implying that the observedsecondary component is a co-moving late-type dwarf. With a projected separationof 11 AU and nearly equal-magnitude components, Gliese 337CD has propertiessimilar to other known companion and field substellar binaries. Its longorbital period (estimated to be ~140-180 yr) inhibits short-term astrometricmass measurements, but the Gliese 337CD system is ideal for studying the L/Ttransition at a fixed age and metallicity. From a compilation of all knownwidely separated (>~100 AU) stellar/brown dwarf multiple systems, we findevidence that the binary fraction of brown dwarfs in these systems is notablyhigher than that of field brown dwarfs, 45(+15)(-13)% versus 18(+7)(-4)% foranalogous samples. We speculate on possible reasons for this difference,including the possibility that dynamic (ejection) interactions which may formsuch wide pairs preferentially retain binary secondaries due to their greatercombined mass and/or ability to absorb angular momentum.Comment: 7 pages, 2 figures, accepted for publication in AJ, June 200