THE KINEMATICS OF LITHIUM-RICH, ACTIVE LATE-TYPE STARS - EVIDENCE FORA LOWMASS LOCAL ASSOCIATION

An EUV-selected sample of late-type stars has been observed for lithiu m abundances and radial velocity variations. It is found that essentia lly all of the single stars have lithium abundances comparable to or g reater than late-type stars in the Pleiades. These observations have c onfirmed the hypothesis that a high proportion of the most coronally a ctive, late-type stars are Li-rich, because they are young, have not y et spun down, and consequently exhibit enhanced dynamo activity. From these data and other activity-selected samples in the literature, a Li -rich sample of single stars has been chosen, which, by comparison wit h open cluster Li abundances and rotation rates, is substantially youn ger than 300 Myr. The kinematics of this sample has been investigated, and from the radial velocities a one-dimensional dispersion of only 5 .7 km s(-1) is found, about a centroid space motion extremely similar to that of a group of young open clusters and nearby B stars, known as the Local Association. Consideration of the space motions confirms th at, if this low-mass Local Association can be represented by a three-d imensional velocity dispersion of about 10 km s(-1) then the majority of the Li-rich stars are members. The origin of the Local Association is still obscure, but a number of suggestions are put forward, includi ng ejection of stars from nearby open clusters, the disruption of pre- existing clusters, or the dissolution of the unbound remnants from one or more star formation regions.