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Astron. Astrophys. 354, 77-85 (2000)

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An investigation of the revised CORS method based on theoretical models

V. Ripepi 1, G. Russo 2,3, G. Bono 4 and M. Marconi 1

1 Osservatorio Astronomico di Capodimonte, Via Moiariello 16, 80131 Napoli, Italy
2 Dipartimento di Fisica, Università della Calabria, Arcavacata di Rende, 87036 Cosenza, Italy
3 CDS Università di Napoli Federico II, Complesso Monte S. Angelo, 80126 Napoli, Italy
4 Osservatorio Astronomico di Roma, Via Frascati 33, 00040 Monte Porzio Catone, Italy

Received 19 October 1998 / Accepted 11 November 1999

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 [FORMULA] bands or on [FORMULA] 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.

Finally, a slight discrepancy between "computed" and "theoretical" radii of a Bump Cepheid supports the exclusion of these pulsation phases in both BW and CORS analyses. In fact, we found that the assumption of quasi-static approximation is no longer valid during the pulsation phases in which appears the bump.

Key words: stars: distances – stars: fundamental parameters – stars: oscillations – stars: variables: Cepheids

Send offprint requests to: V. Ripepi (ripepi@na.astro.it)

This article contains no SIMBAD objects.

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© European Southern Observatory (ESO) 2000

Online publication: January 31, 2000
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