Orbital structure of self-consistent triaxial stellar systems

AQUILANO, ROBERTO O.; MUZZIO, JUAN CARLOS; NAVONE, HUGO D.; ZORZI, ALEJANDRA F.

CELESTIAL MECHANICS & DYNAMICAL ASTRONOMY

Springer

Año: 2007 vol. 99 p. 307 - 324

0923-2958

We used a multipolar code to create, through the disipationless collapses of systems of 1,000,000 particles, three self{consistent triaxial stellar systems with axial ratios corresponding to those of E4, E5 and E6 galaxies. The E5 and E6 models have small, but signi cant, rotational velocities although their total angular momenta are zero, that is, they exhibit gure rotation; the rotational velocity decreases with decreasing attening of the models and for the E4 model it is essentially zero. Except for minor changes, probably caused by unavoidable relaxation eects, the systems are highly stable. The potential of each system was subsequently approximated with interpolating formulae yielding smooth potentials, stationary for the non{rotating model and stationary in the rotating frame for the rotating ones. The Lyapunov exponents could then be computed for randomly selected samples of the bodies that make up the different systems, allowing the recognition of regular and partially and fully chaotic orbits. Finally, the regular orbits were Fourier analyzed and classiffed using their locations on the frequency map. As it could be expected, the percentages of chaotic orbits increase with the attening of the system. As one goes from E6 through E4, the fraction of partially chaotic orbits relative to that of fully chaotic ones increases, with the former surpasing the latter in model E4; the likely cause of this behavior is that triaxiality diminishes from E6 through E4,  the latter system being almost axially symmetric. We especulate that some of the partially chaotic orbits may obey a global integral akin to the long axis component of angular momentum. Our results show that is perfectly possible to have highly stable triaxial models with large fractions of chaotic orbits, but such systems cannot have constant axial ratios from center to border: a slightly attened reservoir of highly chaotic orbits seems to be mandatory for those systems.