Pulsational M-V versus [Fe/H] relation(s) for globular cluster RR Lyrae variables

We use the results from recent computations of updated non-linear convectiv e pulsating models to constrain the distance modulus of Galactic globular c lusters through the observed periods of first-overtone (RRc) pulsators. The resulting relation between the mean absolute magnitude of RR Lyrae stars [ M-V(RR)] and the heavy element content [Fe/H] appears well in the range of several previous empirical calibrations, but with a non-linear dependence o n [Fe/H] so that the slope of the relation increases when moving towards la rger metallicities. On this ground, our results suggest that metal-poor ([F e/H]<-1.5) and metal-rich ([Fe/H]>-1.5) variables follow two different line ar [M-V(RR)]-[Fe/H] relations. Application to RR Lyrae stars in the metal-p oor globular clusters of the Large Magellanic Cloud (LMC) provides an LMC d istance modulus of the order of 18.6 mag, thus supporting the 'long' distan ce scale. The comparison with recent predictions based on updated stellar e volution theory is briefly presented and discussed.