Letter to the Editor

The influence of chemical composition on the properties of Cepheid stars^*,**

I. Period–Luminosity relation vs. iron abundance

¹ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany e-mail: mromanie@eso.org
² Instituut voor Sterrenkunde, PACS - ICC, Celestijnenlaan 200B, 3001 Leuven, Belgium
³ INAF - Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monte Porzio Catone, Italy
⁴ Observatoire de Paris-Meudon, GEPI, 61 avenue de l'Observatoire, 75014 Paris, France

Received: 11 October 2004
Accepted: 20 November 2004

Abstract

We have assessed the influence of the stellar iron content on the Cepheid Period–Luminosity (PL) relation by relating the V band residuals from the Freedman et al. ([CITE]) PL relation to [Fe/H] for 37 Galactic and Magellanic Clouds Cepheids. The iron abundances were measured from FEROS and UVES high-resolution and high-signal to noise optical spectra. Our data indicate that the stars become fainter as metallicity increases, until a plateau or turnover point is reached at about solar metallicity. Our data are incompatible with both no dependence of the PL relation on iron abundance, and with the linearly decreasing behavior often found in the literature (e.g. Kennicutt et al. [CITE]; Sakai et al. [CITE]). On the other hand, non-linear theoretical models of Fiorentino et al. ([CITE]) provide a fairly good description of the data.