Numerical experiments on the oscillations of a rotating, axisymmetric galaxy

Abstract

view Abstract Citations (11) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Numerical Experiments on the Oscillations of a Rotating, Axisymmetric Galaxy Miller, R. H. ; Vandervoort, Peter O. ; Welty, Daniel E. ; Smith, B. F. Abstract In a sequence of self-consistent, three-dimensional numerical experiments, we have studied modes of oscillation in six rotating, axisymmetric N-body systems. The experimental systems are realizations of theoretical models of galaxies which are stellar-dynamical counterparts of uniformly rotating polytropes of index equal to 0.5. The ratio of the rotational kinetic energy to the gravitational potential energy ranges from 0.13 to 0.20 in the systems investigated. As originally constructed, our experimental systems are not quite in equilibrium; they oscillate axisymmetrically. We attribute this behavior to the approximations involved in our numerical realizations of the theoretical models, and we interpret the oscillations as superpositions of a mode of radial pulsation and a Kelvin-like mode of oscillation. When we isolate these modes by forming certain linear combinations of the components of the moment of inertia tensor, we find that their experimental frequencies agree very well with theoretical predictions derived with the aid of tensor virial methods. We have suppressed the axisymmetric oscillations of the experimental systems by perturbing the initial conditions for each experiment in accordance with the virial representation of the radial and Kelvin-like modes. With these modes suppressed, the states of the experimental systems are very steady. We have separately excited three toroidal modes (bar modes) in the steady state systems. In each such experiment, we excite the desired mode by perturbing the initial conditions in accordance with the virial representation of the mode. The experimental frequencies and growth rates of the toroidal modes also agree very well with theoretical predictions. We find that the experimental systems are dynamically unstable with respect to a toroidal mode when the ratio of the rotational kinetic energy to the gravitational potential energy exceeds a value lying between 0.16 and 0.17; the predicted value of that ratio for the onset of instability is 0.166. Publication: The Astrophysical Journal Pub Date: July 1989 DOI: 10.1086/167579 Bibcode: 1989ApJ...342..105M Keywords: Computational Astrophysics; Galactic Rotation; Galactic Structure; Many Body Problem; Astronomical Models; Gravitational Effects; Kinetic Energy; Moments Of Inertia; Perturbation; Tensor Analysis; Astrophysics; GALAXIES: INTERNAL MOTIONS; GALAXIES: STRUCTURE; NUMERICAL METHODS; STARS: STELLAR DYNAMICS full text sources ADS |