Orbital Structure of Self-Consistent Triaxial Stellar Systems

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

Atenas, Grecia

Workshop; Chaos in Astronomy 2007; 2007

Research Center for Astronomy, Academy of Athens

We created five self-consistent triaxial stellar systems through the cold disipationless collapse of 1,000,000 particles whose evolution was followed with a multipolar code. Three of them have semiaxial ratios corresponding to those of E4 through E6 elliptical galaxies, while the other two are equivalent to the E4 and E6 models but with greater concentration, i.e., they represent cuspy models. The E4 models are close to axisymmetrical and prolate. The E6 models have significant figure rotation (their total angular momentum is zero); the rotation of the E5 model is barely significant and that of the E4 models is essentially zero. Except for unavoidable relaxation effects, the systems remain highly stable over periods comparable to a Hubble time. Smooth potentials (stationary or stationary in the rotating frame) were obtained by interpolating formulae, about 3,000 bodies were randomly selected for each model and their positions and velocities were used to compute orbits. Lyapunov exponents were used to classify the orbits as regular, partially or fully chaotic. Regular orbits were Fourier analyzed and classified according to their positions on the frequency map. The fraction of regular orbits decreases from E4 to E6, the cuspy models having the lowest fractions. The relative numbers of partially to fully chaotic orbits increase as one goes from E6 to E4, a likey consequence of approaching to rotational symmetry. Our results show that it is perfectly possible to have highly stable triaxial models with large fractions of chaotic orbits, provided that their axial ratios increase from center to border.