Involved people at OAB: Cacciari, Clementini.
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, ASP Conf. Ser. Vol 203, 176). This analysis is presently being performed on a group of field RR Lyraes at [Fe/H]=--1.5 in order to derive the zero-point of the absolute luminosity at this metallicity, and derive an accurate estimate of the distance to the LMC, that contains many RR Lyraes for which good quality photometric data are available (Clementini et al. 2000, AJ, submitted). Within this framework, we have started an observing program in the IR (K-band) of a few RR Lyraes in the globular clusters M3 and M92 using ARNICA at the TNG and the IR detector at the AZT24 telescope of Campo Imperatore. Along with accurate radial velocities that are planned to be taken with SARG, this database will be used to apply the B-W method directly on RR Lyraes in these two very interesting globular clusters. 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 that were obtained with smaller telescopes and less powerful detectors.