RR LYRAE VARIABLE-STARS - PULSATIONAL CONSTRAINTS RELEVANT TO THE OOSTERHOFF CONTROVERSY

A solution to the old Oosterhoff controversy is proposed on the basis of a new theoretical pulsational scenario concerning RR Lyrae cluster variables (Bone and coworkers). We show that the observed constancy of the lowest pulsation period in both Oosterhoff type I and Oosterhoff type II prototypes (M3, M15) can be easily reproduced only by assuming the canonical evolutionary horizontal-branch luminosity levels of these Galactic globular clusters and therefore by rejecting the Sandage period-shift effect (SPSE).