The ballistic particle model and the vertex deviation of young stars near the sun

The ballistic particle model is used to predict the velocities of young stars near the sun. The model is consistent with observations in that it predicts that O and B stars will have a distribution of velocities in which the direction of maximum velocity dispersion points toward approximately 320 degrees. The predicted values of the vertex deviation away from the galactic center and the velocity centroid with respect to the dynamical, local standard of rest are very near the observed values. The sense of the vertex deviation predicted by the model is seen to be caused by the assumption that the stars form dense molecular clouds launched from the spiral arms at the postshock velocity which has a radial component directed toward the galactic center; consequently, the vertex deviates toward the direction of increasing galactic longitude.