  We present photometric, astrometric and spectroscopic observations of the
nearby (9.8 pc) low-mass binary Gl 569Bab (in turn being a companion to the
early-M star Gl 569A), made with the Keck adaptive optics facility. Having
observed Gl 569Bab since August 1999, we are able to see orbital motion and to
determine the orbital parameters of the pair. We find the orbital period to be
892 +/- 25 days, the semi-major axis to be 0.90 +/- 0.02 AU, the eccentricity
to be 0.32 +/- 0.02 and the inclination of the system to be 34+/- 3 degrees
(1-sigma). The total mass is found to be 0.123 (-0.022/+0.027) Msun (3-sigma).
In addition, we have obtained low resolution (R=1500-1700) near-infrared
spectra of each of the components in the J- and K-bands. We determine the
spectral types of the objects to be M8.5V (Gl 569Ba) and M9V (Gl 569Bb) with an
uncertainty of half a subclass. We also present new J- and K-band photometry
which allows us to accurately place the objects in the HR diagram. Most likely
the binary system is comprised of two brown dwarfs with a mass ratio of 0.89
and with an age of approximately 300 Myr.
