Triaxial equilibrium models for elliptical galaxies with slow figure rotation

An earlier numerical construction of a triaxial model for a stellar system in dynamical equilibrium has been extended, first by adding a slow figure rotation, and second by adding rotational streaming on Z-tube orbits. The figure rotation was kept low so that the main resonances, including the outer edge of Binney's instability strip, fall outside the model. This figure rotation induces weak rotational streaming, prograde on box orbits and retrograde on X-tube orbits. The resulting net streaming has a very low velocity (although substantially higher than the figure rotation by itself) and a complicated pattern, prograde in the inner portion and retrograde in the outer portion. The addition of prograde Z-tube orbits, circling around the short (Z) rotation axis, introduces strong rotational streaming on these orbits. The net effect of this streaming is, however, substantially diluted by the box orbits, which are needed for the support of the triaxial figure. The maximum net rotational streaming velocity thus permitted for the figure here used (1:1.25:2) appears sufficient to model the observed rotation of most giant ellipticals.