The Dependency of the Cepheid Period-Luminosity Relation on Chemical Composition

TL;DR

This study demonstrates that the Cepheid Period-Luminosity Relation varies with chemical composition, showing a significant dependence in the V band and a lesser one in the K band, impacting distance measurements.

Contribution

It provides direct evidence of the non-universality of the Cepheid Period-Luminosity Relation based on detailed abundance analysis and high-quality spectra.

Findings

Metal-rich Cepheids are approximately 0.3 mag fainter in V band.

The dependency of the PL relation on metallicity is less in the K band.

The significance of the dependency depends on precise distance measurements.

Abstract

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.