On the evolution of moving groups: an application to the Pleiades moving group

The disruption of stellar systems, such as open clusters or stellar complexes, stands out as one of the most reasonable physical processes accounting for the young moving groups observed in the solar neighbourhood. In the present study we analyse some of the mechanisms that are important in the kinematic evolution of a group of unbound stars, such as the focusing phenomenon and its ability re, recover the observed moving group's velocity dispersions, and the efficiency of disc heating and galactic differential rotation in disrupting unbound stellar systems. Our main tools used to perform this analysis are both the epicycle theory and the integration of the equations of motion using a realistic gravitational potential of the Galaxy. The study of the trajectories followed by stars in each of the Pleiades moving group substructures found by Asiain et al. (1999) allows us to determine their stellar spatial and velocity distribution evolution. The kinematic properties of these substructures are compared to those of a simulated stellar complex which has evolved under the influence of the galactic gravitational potential and the disc heating, We conclude that a constant diffusion coefficient compatible with the observational heating law is able to explain the velocity and spatial dispersions of the Pleiades moving group substructures that are younger than similar to 1.5 . 10(8) yr.