We have used the NICMOS NIC1 camera on the Hubble Space Telescope to obtain high angular resolution images of 52 ultracool dwarfs in the immediate Solar Neighbourhood .
Nine systems are resolved as binary , with component separations from 1.5 and 15 AU .
Based on current theoretical models and empirical bolometric corrections , all systems have components with similar luminosities , and , consequently , high mass ratios , q > 0.8 .
Limiting analysis to L dwarfs within 20 parsecs , the observed binary fraction is 12 ^ { +7 } _ { -3 } \% .
Applying Bayesian analysis to our dataset , we derive a mass-ratio distribution that peaks strongly at unity .
Modelling the semi-major axis distribution as a logarithmic Gaussian , the best fit is centered at log a _ { 0 } = 0.8 AU ( \sim 6.3 AU ) , with a ( logarithmic ) width of \pm 0.3 .
The current data are consistent with an overall binary frequency of \sim 24 \% .