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We present analysis of Hubble Space Telescope images of 82 nearby fieldlate-M and L dwarfs. We resolve 13 of these systems into double M/L dwarfsystems and identify an additional possible binary. Combined with previousobservations of 20 L dwarfs, we derive an observed binary fraction forultracool dwarfs of 17+4-3%, where the statistics included systems withseparations in the range 1.6-16 A.U. We argue that accounting for biases andincompleteness leads to an estimated binary fraction 15+-5% in the range 1.6-16A.U. No systems wider than 16 A.U. are seen, implying that the wide companionfrequency is less than 1.7%; the distribution of orbital separation is peakedat ~2-4 A.U. and differs greatly from the G dwarf binary distribution. Indirectevidence suggests that the binary fraction is ~5+-3% for separations less than1.6 A.U. We find no evidence for differences in the binary fraction betweenstellar late-M and L dwarfs and substellar L dwarfs. We note, however, that thewidest (>10 A.U.) systems in our sample are all of earlier (M8-L0) spectraltype; a larger sample is needed determine if this is a real effect. One systemwith a spectral type of L7 has a secondary that is fainter in the HST F814Wfilter but brighter in F1042M; we argue that this secondary is an early-Tdwarf.Comment: To appear in June 2003 Astronomical Journa

Hubble Space TelescopeObservations of Binary Very Low Mass Stars and Brown Dwarfs