Activity and kinematics of ultracool dwarfs

Using new proper-motion measurements and spectrophotometric distance estimates, we calculate tangential velocities. The sample has a mean tangential velocity of <V_tan_>=31.5km/s, a velocity dispersion of {sigma}_tan_=20.7km/s, and a maximum tangential velocity of V_tan_=138.8km/s.

These kinematic results are in excellent agreement with previous studies of ultracool dwarfs in the local solar neighborhood. H{alpha} emission, an indicator of chromospheric activity, was detected in 63 of 81 late-M dwarfs and in 16 of 69 L dwarfs examined. We find a lack of correlation between activity strength, measured by log(FH{alpha}/Fbol), and V_tan_, although velocity distributions suggest that the active dwarfs in our sample are slightly younger than the inactive dwarfs.