  AB Dor C, a low-mass companion to the young star AB Dor A has recently been
imaged. Direct detection and astrometric observations have been used to solve
the AB Dor C orbit and obtain a dynamical mass estimate. Near-infrared
magnitudes and effective temperatures from models have then been compared with
observed values. Models and observations disagree at more than the 2 sigma
level. This result prompts Close et al. 2005 to claim that models are
overestimating young low-mass object luminosities by roughly a factor of two.
This claim is based on the hypothesis that the detected source, AB Dor C, is a
single object. Another possible interpretation of the data that was not
considered is that AB Dor C is an unresolved binary brown dwarf. Considering
that 21 brown dwarfs companions have been found to date around stars and that
three of them are confirmed or potential brown dwarf binaries (Gl569Ba & Bb,
GL564B & C and Indi Ba & Bb), this suggests that brown dwarf binaries may
constitute a significant fraction (14% +/- 8%) of the brown dwarf population
around stars. For these reasons, the possibility that AB Dor C is an unresolved
binary brown dwarf deserves attention.
