The hubble space telescope key project on the extragalactic distance scale. XIII. The metallicity dependence of the cepheid distance scale1-2

Abstract

Uncertainty in the metal-abundance dependence of the Cepheid variable period-luminosity (PL) relation remains one of the outstanding sources of systematic error in the extragalactic distance scale and in the Hubble constant. To test for such a metallicity dependence, we have used the Wide Field Planetary Camera 2 (WFPC2) on the Hubble Space Telescope (HST) to observe Cepheids that span a range in oxygen abundance of 0.7 ± 0.15 dex in two fields in the nearby spiral galaxy M101. A differential analysis of the PL relations in V and I in the two fields yields a marginally significant change in the inferred distance modulus on metal abundance, with σ(m-M)0/σ[O/H] = -0.24 ± 0.16 mag dex-1. The tr..