STELLAR SURFACE OSCILLATIONS UNDER THE ACTION OF HYDRODYNAMICAL PERTURBATIONS

The problem of stellar surface oscillations under the action of pertur bations in the inner layers of the star is considered. A one-dimension al hydrodynamical model is adopted to describe relatively short (compa red with the stellar radius) perturbations of gas in a non-stationary gravity field. The Legendre transformation technique is used to obtain exact solutions describing the star's surface oscillations. It is sho wn that if the perturbations in the inner layers of the star have smal l energy, then the extreme characteristics of the star surface oscilla tions (displacement and velocity) do not depend on the nonlinearity of the problem, and thus, they can be calculated in the frame-work of a linear hydrodynamical model. The criterion for breaking of the wave co ming to the star's surface is obtained. It is found that this criterio n can be defined by solving the linear problem and therefore having a very clear physical sense (the ratio of the wave acceleration to the a cceleration due to gravity). It is shown that the variable part of the gravity field is responsible for gas oscillations as a whole, which d oes not influence decisively the wave dynamics of the stellar surface. The spectrum of stellar surface oscillations is calculated.