The effects of galactic disk oscillations on the motion of the stars confined to the axis of rotating symmetry.

Details The effects of galactic disk oscillations on the motion of the stars confined to the axis of rotating symmetry. The effects of galactic disk oscillations on the motion of the stars confined to the axis of rotating symmetry.

Dec 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996a%26a...316...79f&link_type=abstract

Astronomy and Astrophysics, v.316, p.79-88

Astronomy and Astrophysics

Astrophysics

3

Celestial Mechanics, Stellar Dynamics, Chaos, Galaxy: Kinematics And Dynamics, Galaxies: Kinematics And Dynamics

Scientific paper

In this paper we discuss the effects of galactic disk oscillations on the motion of the stars, which are confined to the axis of rotating symmetry, with the potential generated by an oscillating Kuzmin disk and a logarithmic halo {PHI}=-1/1+ɛsint+|z|+1/2ln(1+z^2^) , where t represents the time variable, z the coordinate of a star in the usual cylindric coordinate system, ɛ({in}[0,1)) the amplitude of the disk oscillation. The system involved is a Hamiltonian system with 3/2 degrees of freedom. We find that, when ɛ=0.01, the surface of section at t=0 (mod2π) is divided into two parts. One is a connected ordered region which contains the origin (z,p)=(0,0) and is mainly covered by invariant curves surrounding (0,0); outside this ordered region, there is no invariant curve surrounding (0,0) and the system behaves chaotically. In the ordered region, one of the interesting phenomena is that the s-island chains with s being odd are much narrower than those with s even. There are escape trajectories in the chaotic region. As ɛ increases, the ordered region persists but becomes smaller due to the chaotic region expanding inwards. And in the ordered region, the area occupied by island chains, as well as that occupied by chaotic separatrix layers, increases with ɛ. The above numerical results have some astronomical implications. The most important one is that all the stars with initial conditions in the ordered region will remain near the disk plane while most stars in the chaotic region could be driven by the oscillating disk to escape from the galaxy. lt is plausible that there is a correlation between the amplitude of the disk oscillation and the thickness of the disk at the center - in the sense that a galaxy with large amplitude of disk oscillation tends to be thin at the center.

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