QUASI-REGULAR SPECTRAL FEATURES OF THE STRONGLY CHAOTIC FERMI RESONANT SYSTEM

Numerical evidence is reported of the quasiregular power spectra in th e strongly chaotic system of coupled Morse and harmonic oscillators wi th the 1:2 frequency ratio. The spectra are shown to consist of a ''re gular'' part, characterized by sharp peaks and a chaotic one which res embles a smooth chaotic background. The regular part does not seem to be related to the visible islands of stable motion as is the case of t he standard map. The observed regularity of the spectra is shown to be associated with the repeated trapping of the chaotic trajectory by th e localized regions of marginal stability. The appearance of such regi ons is the direct consequence of the global tangent bifurcations near the borderline of the system. The analysis of the spectra of local Lya punov exponents and periodic orbits analysis seem to account for the m ost important qualitative features of the underlying chaotic dynamics. In particular we show that a relatively small number of low-period sa ddle-center pairs born in tangent bifurcations is sufficient to charac terize marginally stable sets and to determine their recurrence proper ties as well.