The influence of chemical composition on the properties of Cepheid stars I - Period-Luminosity relation vs iron abundance

TL;DR

This study investigates how the iron content in Cepheid stars affects their Period-Luminosity relation, revealing a non-linear dependence that challenges previous assumptions of no or linear metallicity effects.

Contribution

It provides empirical evidence that the Cepheid PL relation depends non-linearly on iron abundance, supporting non-linear theoretical models over linear or no-dependence hypotheses.

Findings

Stars become fainter with increasing metallicity up to solar levels.

Data contradicts models with no metallicity dependence or linear decrease.

Non-linear models align well with observed data.

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 (2001) 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 1998, Sakai et al 2004). On the other hand, non-linear theoretical models of Fiorentino et al (2002) provide a fairly good description of the data.