NONLINEAR PROPERTIES OF DOUBLE-MODE PULSATORS

The generalized Fourier phase difference between the components of a m ultiperiodic oscillation is presented, and it is applied to the double -mode Cepheid light curve parameters. It is shown that the generalized phase difference of the combination frequency terms can give useful i nformation on the nonlinear characteristics of the pulsation and on th e possible presence of resonances between pulsation modes as in the ca se of the classical phase differences used for single-mode pulsators. Furthermore, it is shown the utility of the qualitative interpretation of the main characteristics of the Fourier phases in the framework of the nonlinear adiabatic treatment of double-mode pulsation on the ana logy of single-mode pulsation.