Gravitational instability of perturbations in a background nonlinear nonstationary model of a disklike system. III. Large-scale bending oscillations modes

We study the gravitational instability of large-scale bending modes of vertical oscillations in the background of a composite non-stationary model of disk-like galaxies. A non-stationary analogue of the dispersion equation for vertical oscillations of the model are found in the general case. This equation is studied for themain large-scale oscillation modeswhich are the most widespread types of bendings, namely, N and S-shaped, asymmetric, dome-shaped, U-shaped and precession bendings. Critical diagrams are constructed for the dependence of the initial virial ratio on the superposition parameter for different values of the rotation parameter of a non-stationary model for these modes. Also, a comparative analysis of the instability growth rates is carried out for the oscillation modes which lead to the appearance of these bendings in the background of the model under study.