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

The disruption of stellar systems, such as open clusters or stellar complex es, stands out as one of the most reasonable physical processes accounting for the young moving groups observed in the solar neighbourhood. In the pre sent study we analyse some of the mechanisms that are important in the kine matic evolution of a group of unbound stars, such as the focusing phenomeno n and its ability re, recover the observed moving group's velocity dispersi ons, 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 mov ing group substructures found by Asiain et al. (1999) allows us to determin e their stellar spatial and velocity distribution evolution. The kinematic properties of these substructures are compared to those of a simulated stel lar complex which has evolved under the influence of the galactic gravitati onal potential and the disc heating, We conclude that a constant diffusion coefficient compatible with the observational heating law is able to explai n the velocity and spatial dispersions of the Pleiades moving group substru ctures that are younger than similar to 1.5 . 10(8) yr.