We present a radial-velocity study of the triple-lined system Gliese 644 and derive spectroscopic elements for the inner and outer orbits with periods of 2.9655 and 627 days .
We also utilize old visual data , as well as modern speckle and adaptive optics observations , to derive a new astrometric solution for the outer orbit .
These two orbits together allow us to derive masses for each of the three components in the system : M _ { \mathrm { A } } = 0.410 \pm 0.028 ( 6.9 % ) , M _ { \mathrm { Ba } } = 0.336 \pm 0.016 ( 4.7 % ) , and M _ { \mathrm { Bb } } = 0.304 \pm 0.014 ( 4.7 % ) M _ { \odot } .
We suggest that the relative inclination of the two orbits is very small .
Our individual masses and spectroscopic light ratios for the three M stars in the Gliese 644 system provide three points for the mass-luminosity relation near the bottom of the Main Sequence , where the relation is poorly determined .
These three points agree well with theoretical models for solar metallicity and an age of 5 Gyr .
Our radial velocities for Gliese 643 and vB 8 , two common-proper-motion companions of Gliese 644 , support the interpretation that all five M stars are moving together in a physically bound group .
We discuss possible scenarios for the formation and evolution of this configuration , such as the formation of all five stars in a sequence of fragmentation events leading directly to the hierarchical configuration now observed , versus formation in a small N cluster with subsequent dynamical evolution into the present hierarchical configuration .