An investigation of the revised CORS method based on theoretical models

Abstract

Direct measurements of Cepheid radii are a key for understanding the physical structure of these variables, and in turn for constraining their pulsation properties. In this paper we discuss the numerical experiments we performed for testing the accuracy of Cepheid radii obtained by adopting both the pure Baade-Wesselink (BW) method and the revised CORS method, as well as the consistency of the physical assumptions on which these methods are based. We applied both the BW and the revised CORS methods to the synthetic light, color and radial velocity curves predicted by Cepheid full amplitude, nonlinear, convective models at solar chemical composition. We found that these methods systematically either underestimate or overestimate "theoretical" radii if radius determinations are based on optical (BVR) bands or on (VJK) bands, respectively. At the same time, current simulations suggest that CORS radii are in very good agreement with "theoretical" radii if the surface brightness is calibrated by adopting a bidimensional fit of atmosphere models which accounts for temperature, gravity, and bolometric correction variations along the pulsation cycle.