Pulsations of model RR Lyrae stars

Radial pulsations of models of RR Lyrae stars are studied in linearized nonadiabatic theory. Convection in the hydrogen and helium ionization zones is treated by use of a time-dependent generalization of mixing-length theory. In a series of models of constant mass, luminosity, and composition, effective temperature is varied as a parameter. It is found, in agreement with previous work, that models in the instability strip are pulsationally unstable. Cooler modesl, however, are stabilized by the convection. Very cool models with deep convective envelopes are nearly neutrally stable to pulsation.