SPECTRAL-ANALYSIS OF THE STOCHASTIC ORBITS IN TRIAXIAL STELLAR-SYSTEMS WITH FIGURE ROTATION

A semi-stochastic orbit does not hold any exact integrals besides the Hamiltonian, but is confined in a definite region in the phase space a nd thus it gives approximately stationary contribution to the density model of triaxial elliptical galaxies. On the other hand, a fully stoc hastic orbit shows a time variation of the shape, which leads the unst ationary contribution to the density. Hence, before the construction o f the density model, we have to classify the orbits into semi-stochast ic and fully stochastic orbits in a galactic potential. In order to ex tract the characteristics of the semi-stochastic orbits, we define the peak indicator which allows us to identify the most prominent peak, a nd carry out a successive subtraction of the prominent peaks until the total power of the residual becomes 10 % of the original one. The fre quencies of the prominent peaks are plotted in the spectral diagram, w hich helps us to understand the evolution of the stochasticity of orbi ts. Compared with other characteristics of orbits, our method of the s pectral analysis can yield enough information about orbital stochastic ity. Since this method requires much less calculative time than calcul ating Lyapunov exponents, it is suitable for classification of the orb its in constructing the galactic models.