Abstract

We analyze the kinematical histories of stars within 20 pc of the Sun, for which three-dimensional spatial coordinates and three-dimensional velocity vectors are available. From this sample, we extract members of stellar kinematical groups (SKGs) in the following manner. First, in the three-dimensional velocity space centered on the local standard of rest, we consider a sphere with a radius of 8 km s^-1 centered on the mean velocity vector of a particular SKG. Around each SKG velocity center, we have found a significant excess of stars compared to background stars. For each candidate, in the three-dimensional spatial coordinate space, its trajectory is traced back in time by the age of the relevant SKG, to estimate the distance from the SKG center at the time of the SKG's birth by the epicycle approximation and vertical harmonic motion. It often happens that a star is a candidate member of multiple SKGs. Then we rank the candidacy to multiple SKGs based on the smallness of distance separations. In this manner, we have kinematically selected 74 candidate members of SKGs out of a sample of 383 stars. If we take into account stellar properties, the number is reduced to 68.