Theoretical Models for Classical Cepheids: II. Period-Luminosity, Period-Color and Period-Luminosity-Color Relations

We present and discuss theoretical pulsational predictions concerning the properties of Classical Cepheids. The computations have been performed for three different chemical compositions taken as representative of Cepheids in the Magellanic Clouds and in the Galaxy. The resulting PL relations are significantly dependent on metallicity, with the amplitude of the metallicity effect decreasing at the longer wavelength. At variance with several empirical suggestions appeared in the literature, we find that at fixed period the metal-rich pulsators should be fainter than the metal-poor ones. Tight Period-Luminosity-Color relations are derived for both visual and near-infrared photometric bands. We present a preliminary use of our relations to evaluate the distance modulus of the Magellanic Clouds.