RR lyrae variables in Galactic globular clusters V. The case of M 3 pulsators

We use our synthetic Horizontal Branch (HB) procedure to approach the often debated problem of how adequate canonical HB stellar models are to account for the observed peaked distribution of RR Lyrae fundamentalised periods in the globular cluster M 3. We find that by assuming a suitable bimodal mass distribution, canonical models do account for the observed period distribution. In particular, the best fit model, out of nine random extractions, reaches a 99.9% Kolmogorov-Smirnov (KS) probability. We also attempt to predict the relative distribution of variables in fundamental and first overtone pulsators, reaching a satisfactory agreement. However, one finds that canonical models outnumber the observed number of red HB stars by roughly a factor of two. Possible solutions for this discrepancy are outlined. Alternative evolutionary scenarios are also briefly discussed.