We present preliminary astrometric results for the closest known brown dwarf binary to the Sun : \varepsilon Indi Ba , Bb at a distance of 3.626 pc .
Via ongoing monitoring of the relative separation of the two brown dwarfs ( spectral types T1 and T6 ) with the VLT NACO near-IR adaptive optics system since June 2004 , we obtain a model-independent dynamical total mass for the system of 121 M _ { Jup } , some 60 \% larger than the one obtained by McCaughrean et al .
( 2004 ) , implying that the system may be as old as 5 Gyr .
We have also been monitoring the absolute astrometric motions of the system using the VLT FORS2 optical imager since August 2005 to determine the individual masses .
We predict a periastron passage in early 2010 , by which time the system mass will be constrained to < 1 M _ { Jup } and we will be able to determine the individual masses accurately in a dynamical , model-independent manner .