Improvement of the CORS method for Cepheids radii determination based on Strömgren photometry

¹ INAF - Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy e-mail: [ruoppo;marcella]@na.astro.it
² Dipartimento di scienze fisiche università di Napoli Federico II, Complesso Monte S.Angelo, 80126 Napoli, Italy e-mail: ale@na.infn.it; e-mail: guirusso@unina.it

Corresponding author: V. Ripepi, ripepi@na.astro.it

Received: 18 December 2003
Accepted: 16 April 2004

Abstract

In this paper we present a modified version of the CORS method based on a new calibration of the Surface Brightness function in the Strömgren photometric system. The method has been tested by means of synthetic light and radial velocity curves derived from nonlinear pulsation models. Detailed simulations have been performed to take into account the quality of real observed curves as well as possible shifts between photometric and radial velocity data. The method has been then applied to a sample of Galactic Cepheids with Strömgren photometry and radial velocity data to derive the radii and a new PR relation. As a result we find (rms = 0.07). The comparison between our result and previous estimates in the literature is satisfactory. Better results are expected from the adoption of improved model atmosphere grids.