The effect of metallicity on the Cepheid P-L relation, from a Baade-Wesselink analysis of SMC Cepheids

We present results based on a Baade-Wesselink analysis of Cepheids in the Small Magellanic Cloud. The Baade-Wesselink analysis provides individual luminosities for these metal-poor Cepheids which combined with recent Baade-Wesselink results from Gieren et al. (1998) on solar metallicity Galactic Cepheids constrain the metallicity effect on the zero-point of the Cepheid P-L relation. A preliminary analysis leads to an effect of dMv / d[Fe/H]= -0.45 +-0.15, metal-rich Cepheids being brighter, in good agreement with several recent independent determinations. An effect of this magnitude reduces significantly the current disagreement between the long and the short distance estimates to the LMC, and favors a shorter value.