Understanding some moving groups in terms of a global spiral shock.

Abstract

We present a schematic model to interpret the kinematics of some major moving groups in the solar neighbourhood. The origin of these groups is assumed to lie in large scale spiral shocks which may be responsible for the spiral arms in the galactic disk, which provide the initial conditions in the velocities of stars formed as a consequence of them. These initial conditions provide a position-velocity relationship which is used to establish an alternative definition of membership in moving groups. Currently available samples suitable for detecting the existence of moving groups are restricted to a small distance from the Sun, where our definition is in practice equivalent to the classical one based on the similarity of the space velocity vectors. However, the difference between both definitions may become relevant when the high quality astrometric data provided by Hipparcos become available. We apply the formulation developed in this paper to a sample of B, A and F stars to derive some parameters of our model.