VERY-LOW MASS M-DWARFS - STARS OR BROWN DWARFS IN DISGUISE

We have used radial velocity and proper motion observations to determi ne the space motions of a sample of 25 low-luminosity M dwarfs. We fin d that the solar motion and velocity dispersions of these stars are si milar to the kinematics of a sample of more luminous, earlier type M d warfs. However, there is evidence to indicate that when objects select ed by photometric criteria alone are considered, the kinematics are mo re characteristic of an similar to 3x10(8) year old population. This s uggests that the faintest known stars may be younger on average than t he local M dwarfs in the Galactic disk, indicating the possible presen ce of a number of brown dwarfs or transition objects in our sample of very low-mass objects.