Characterizing multiplicity in the very low mass ( VLM ) domain is a topic of much current interest and fundamental importance .
Here we report on a near-infrared adaptive optics imaging survey of 31 young brown dwarfs and VLM stars , 28 of which are in the Chamaeleon I star-forming region , using the ESO Very Large Telescope .
Our survey is sensitive enough to detect equal mass binaries down to separations of 0.04–0.07 \arcsec ( \sim 6–10 AU at 160 pc ) and , typically , companions with mass ratios ( q = m _ { 2 } / m _ { 1 } ) as low as 0.2 outside of 0.2 \arcsec ( \sim 30 AU ) .
We resolve the suspected 0.16 \arcsec ( \sim 26 AU ) binary ChaH \alpha 2 and present two new binaries , Hn 13 and CHXR 15 , with separations of 0.13 \arcsec ( \sim 20 AU ) and 0.30 \arcsec ( \sim 50 AU ) respectively ; the latter system is one of the widest VLM systems discovered to date .
We do not find companions around the majority of our targets giving an overall binary frequency of 11 ^ { +9 } _ { -6 } \% , thus confirming the trend for a lower binary frequency with decreasing mass .
By combining our work with previous surveys of VLM objects ( VLMOs ) in other star forming regions , we arrive at the largest sample of young VLMOs ( 72 ) with high angular resolution imaging to date .
Its multiplicity fraction is in statistical agreement with that for VLMOs in the field .
In addition we note that many field stellar binaries with lower binding energies and/or wider cross sections have survived dynamical evolution and that statistical models suggest tidal disruption by passing stars is unlikely to affect the binary properties of our systems .
Thus , we argue that there is no significant evolution of multiplicity with age among brown dwarfs and 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 less likely to be born in fragile multiple systems than solar mass stars or such systems are disrupted very early ( within the first couple of Myr ) .