2888 20160701171712.0 10.1063/1.3246585 DOI ASTROimport-1045 Romaniello, M. 2009 The Dependency of the Cepheid Period-Luminosity Relation on Chemical Composition The dependency of the Cepheid Period-Luminosity Relation on chemical composition at different wavelengths is assessed via direct detailed abundance analysis of Galactic and Magellanic Cepheids, as derived from high resolution, high signal-to-noise spectra. Our measurements span one order of magnitude in iron content and allow to rule out at the ~9 sigma level the universality of the Period-Luminosity Relation in the V band, with metal rich stars being fainter than metal poor ones by ~0.3 mag. The dependency is less pronounced in the K band. Its magnitude and statistical significance decisively depend on detailed distance measurements to individual stars, as inferred via the Infrared Surface Brightness Method. Primas, F. Mottini, M. Pedicelli, S. Lemasle, B. Bono, G. François, P. Groenewegen, M. A. T. Laney, C. D. American Institute of Physics Conference Series 1170 2009 99-101 http://esoads.eso.org/abs/2009AIPC.1170...99R published in NONREF