RR Lyrae variables in Galactic globular clusters

Abstract

We use our synthetic Horizontal Branch (HB) procedure to approach the debated problem concern- ing the adequacy of canonical HB stellar models to account for the observed peaked distribution of RR Lyrae fundamentalised periods in the globular cluster M3. We find that by assuming a suitable bimodal mass distri- bution, canonical models 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 a prediction of the relative distribution of variables in fundamental and first overtone pulsators, reaching a rather satisfactory agreement. However, one finds that canonical models outnumber by roughly a factor of two the observed number of red HB stars. Possible solutions for this discrepancy are outlined. Alternative evolutionary scenarios are also briefly discussed.