Regular and irregular nonlinear pulsation in population II Cepheid models

Linear and nonlinear pulsational properties of radiative stellar models relevant for W Vir, RV Tau, and yellow semiregular variables are surveyed. Masses and luminosities range from 0.4 - 0.8 M_sun; and 200 - 1000 L_sun; respectively. The chemical composition is fixed to X = 0.745, Z = 0.005. Three types of pulsational behavior occur (1) singly periodic pulsations (limit cycles) with a radius variation of one maximum (or minimum) per period which are called regular limit cycles, (2) limit cycles with 2, 4, 8, ... maxima (minima) per repetition period which are called period doubled limit cycles, (3) irregular pulsations which are chaotic in the sense of dynamical systems analysis.