RR Lyrae Stars in Galactic Globular Clusters. II. A Theoretical Approach to Variables in M3

We present predicted relations connecting pulsational and evolutionaryparameters, as based on a wide set of convective pulsating models of RR Lyraestars with Z=0.001, Y=0.24 and mass and luminosity suitable for the ``old''(age $>$ 8 Gyr) variables observed in globular clusters. The relations arecollated with sound constraints on the mass of pulsators, as inferred fromup-to-date evolutionary models of horizontal branch stars, in order to providea self-consistent theoretical framework for the analysis of observed variables.The theoretical predictions are tested through a detailed comparison withmeasurements of RR Lyrae stars in the globular cluster M3. We show that thepredicted relations satisfy a variety of observed data, thus providing a"pulsational" route to the determination of accurate distances to RR Lyrae-richglobular clusters with intermediate metal content. We discuss the effect ofdifferent physical inputs in evolutionary computations, as well as of differentbolometric corrections adopted to convert bolometric luminosity into absolutemagnitude. We show that the constraints inferred by pulsation theory supportthe large value of the mixing-length parameter adopted to fit observed RGB,but, at the same time, they would yield that the luminosity of updated HBmodels is too bright. Such discrepancy is significantly reduced if elementdiffusion is properly taken into account.Comment: 29 pages, 20 postscript figures, accepted for publication on Ap