Evolution of population II stars and radial pulsation period change after the helium flash

Evolutionary computations from the main sequence to the zero-age horizontal branch were done for the star with mass 0.8M⊙. Selected models of the evolutionary sequence were used as initial conditions in solution of the equations of radiation hydrodynamics and time-dependent turbulent convection for radial stellar oscillations. The evolutionary track is shown to cross the pulsational instability strip several times during the last three luminosity maxima of the helium flash. Obtained theoretical estimates of the period change rate are compared with observations of RR Lyrae variables in the globular cluster M3.