On the issue of gravitational instability of the Sun protoplanetary disk. Part II. The dispersion equations

Here it is considered the analytical model for the description of the Sun protoplanetary disk in the initial stage of its evolution proposed in 2006 by A. V. Zabrodin, M. S. Legkostupov, K. V. Manukovskiy et al. The two-dimensional system of equations, which describes the evolution of the protoplanetary disk in its initial stage was created. Linearization of equations of the protoplanetary disk to its Equatorial plane was done. On the basis of the linearized equations there were obtained approximate dispersion equations for the medium of the protoplanetary disk, located in the vicinity of its Equatorial plane.