from the Baade-Wesselink method
The Baade-Wesselink determination of the absolute luminosity of the galactic field RR Lyrae variables is currently being revised in order to test the effects on this technique of the most recent model atmospheres with various approximations in the treatment of convection, different values of turbulent velocity and more complete and accurate opacity tables, as well as the use of the instantaneous gravity along the pulsation cycle (Cacciari et al. 2000). In May 2001 we have obtained with SARG@TNG high resolution spectra of a few RR Lyrae in the GGC M 3, to derive accurate radial velocity curves. Along with IR (K-band) ARNICA data taken in a previous run at the TNG, this database will be used to apply the B-W method directly on RR Lyraes in this very interesting GC. The very few previous studies of this type, that date back to about 10 years ago, did not produce reliable results due to the poor quality of the data, obtained with smaller telescopes and less powerful detectors.