We present the results of a high-resolution spectral differential imaging survey of 12 nearby , relatively young field L dwarfs ( \leq 1 Gyr ) carried out with HST/NICMOS to search for planetary mass companions at small physical separations from their host .
The survey resolved two brown dwarf binaries : the L dwarf system Kelu-1 AB and the newly discovered L/T transition system 2MASS 031059+164815 AB .
For both systems common proper motion has already been confirmed in follow-up observations which have been published elsewhere .
The derived separations of the binaries are smaller than 6 AU and consistent with previous brown dwarf binary statistics .
Their mass ratios of q \geq 0.8 confirm the preference for equal mass systems similar to a large number of other surveys .

Furthermore , we found tentative evidence for a companion to the L4 dwarf 2MASSW 033703-175807 , straddling the brown dwarf/planetary mass boundary and revealing an uncommonly low mass ratio system ( q \approx 0.2 ) compared to the vast majority of previously found brown dwarf binaries .
With a derived minimum mass of 10 M _ { \mathrm { Jup } } to 15 M _ { \mathrm { Jup } } a planetary nature of the secondary can not be ruled out yet .
However , it seems more likely to be a very low mass brown dwarf secondary at the border of the spectral T/Y transition regime , primarily due to its similarities to recently found very cool T dwarfs .
This would make it one of the closest resolved brown dwarf binaries ( 0.087″ \pm 0.015″ , corresponding to 2.52 \pm 0.44 AU at a distance of 29 pc ) with the coolest ( T _ { \mathrm { eff } } \approx 600 - 630 K ) and least massive companion to any L or T dwarf .