A detailed analysis of double-mode RR Lyrae stars:: Further support for a brighter luminosity scale

In order to derive the physical parameters of double-mode RR Lyrae stars in the Galactic globular clusters M15, M68, and IC4499, we fully utilize all observables (periods, apparent magnitudes, and colors) together with linear pulsation models. Except for the zero point of the color-temperature calibration and for the adopted metallicity of the double-mode stars in M15, our method is free from any systematic effects due to ambiguities in the various zero points (i.e., magnitude, bolometric correction, etc.). It is shown that for any "reasonable" chosen metallicity of M15, the so-derived absolute magnitudes are always brighter by some 0.2-0.3 mag than the corresponding Baade-Wesselink values. The difference becomes less than 0.1 mag only for extremely metal deficient compositions of [M/M](M15) < -3.0. Masses are in the range 0.65-0.85 M-circle dot, depending on the cluster and the above-mentioned parameters. These conclusions are essentially independent of the details of the chemical composition (e.g., enhancement of the heavy elements).