Annu. Rev. Astron. Astrophys. 1991. 29: 239-274 Copyright © 1991 by Annual Reviews. All rights reserved

2.3.4 KINEMATICS Eddington (102) already knew that the principal axes of the velocity ellipsoid in a Stäckel model are locally always aligned with the coordinate system in which the motion separates, so that in the central regions the velocity ellipsoid is aligned along the principal axes of the model, while at large distances it is aligned nearly radially. This is seen also in non-separable models with homogeneous cores (234). Solutions of the Jeans equations for axisymmetric separable models have been given recently (74, 107, 109), but the equations for the triaxial case (218) have not been solved. They should provide useful information on the variety of dispersion profiles expected for equilibrium models, which is helpful in modeling kinematic data.