Orbital structure of self-consistent triaxial stellar systems |
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Authors: | Roberto O Aquilano Juan C Muzzio Hugo D Navone Alejandra F Zorzi |
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Institution: | (1) Instituto de Física de Rosario (CONICET-UNR), Observatorio Astronómico Municipal de Rosario and Facultad de Ciencias Exactas, Ingeniería y Agrimensura de la Universidad Nacional de Rosario, Rosario, Argentina;(2) Facultad de Ciencias Astronómicas y Geofísicas, Instituto de Astrofísicade La Plata (UNLP–CONICET), Universidad Nacional de La Plata, La Plata, Argentina |
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Abstract: | We used a multipolar code to create, through the dissipationless 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 significant, rotational velocities although their total angular momenta are zero, that is, they exhibit figure rotation;
the rotational velocity decreases with decreasing flattening of the models and for the E4 model it is essentially zero. Except
for minor changes, probably caused by unavoidable relaxation effects, 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 classified using their locations on the frequency map.
As it could be expected, the percentages of chaotic orbits increase with the flattening 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 surpassing
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
flattened reservoir of highly chaotic orbits seems to be mandatory for those systems. |
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Keywords: | Triaxial stellar systems Figure rotation Stellar orbits Chaotic motion |
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