ON THE APPLICATION OF THE BAADE-WESSELINK METHOD TO RR LYRAE STARS

Some of the assumptions adopted by the Baade-Wesselink (BW) method were tested using a nonlinear, non-local, and time-dependent convective model of RR Lyrae star, transformed into the observative plane through the bolometric corrections and the color-temperature relations recently provided by Kurucz. The magnitudes of cluster variables do not depend strongly on the values of the surface gravity, whereas colors show a substantial dependence throughout the full cycle. It is also shown that velocity gradients are present in the atmosphere on a large part of the pulsation cycle. Finally, it is also confirmed that the method generally adopted to derive the radial velocity of the center of mass directly from the velocity curve is incorrect.