Nonlinear pulsations of discrete stellar models. III. Adiabatic motions of a two-zone model

Oscillations of two-shell model for a star undergoing nonlinear conservative pulsation are compared with those of a low-order approximation of the fully nonlinear model. Behavior of the fully nonlinear model differs significantly from the predictions of the low-order approximation whose equipotential curves show saddle-points not found in the fully nonlinear models. It is concluded that low-order approximations artificially induce strong nonlinear effects and so are not valid indicators of the onset of chaos in conservative models with few degrees of freedom. 22 references