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Characterizing multiplicity in the very low mass (VLM) domain is a topic ofmuch current interest and fundamental importance. Here we report on a near-IRAO imaging survey of 31 young brown dwarfs and VLM stars, 28 of which are inChamaeleon I, using the ESO VLT. Our survey is sensitive enough to detect equalmass binaries down to separations of 0.04-0.07" (6-10 AU at 160 pc) and,typically, companions with mass ratios as low as 0.2 outside of 0.2" (~30 AU).We resolve the suspected 0.16" (~26 AU) binary Cha_Halpha 2 and present two newbinaries, Hn 13 and CHXR 15, with separations of 0.13" (~20 AU) and 0.30" (~50AU); the latter is one of the widest VLM systems discovered to date. We do notfind companions around the majority of our targets, giving a binary frequencyof 11% [+9,-6], thus confirming the trend for a lower binary frequency withdecreasing mass. By combining our work with previous surveys, we arrive at thelargest sample of young VLMOs (72) with high angular resolution imaging todate. Its multiplicity fraction is in statistical agreement with that for VLMOsin the field. In addition we note that many field stellar binaries with lowerbinding energies and/or wider cross sections have survived dynamical evolutionand that statistical models suggest tidal disruption by passing stars isunlikely to affect the binary properties of our systems. Thus, we argue thatthere is no significant evolution of multiplicity with age among brown dwarfsand VLM stars in OB and T associations between a few Myr to several Gyr.Instead, the observations to date suggest that VLM objects are either lesslikely to be born in fragile multiple systems than solar mass stars or suchsystems are disrupted very early.

Multiplicity Among Young Brown Dwarfs and Very Low Mass Stars