Metallicity estimation of MW, SMC and LMC classical Cepheids from the shape of the $V$- and $I$-band light curves

TL;DR

This paper develops empirical relations using Fourier parameters from $V$- and $I$-band light curves to estimate the metallicity of classical Cepheids across different galaxies, aiding galactic archaeology and distance measurements.

Contribution

It introduces new empirical relations for metallicity estimation of Cepheids based on light curve Fourier parameters, applicable in $V$ and $I$ bands, and demonstrates their effectiveness across multiple galaxies.

Findings

Relations accurately estimate mean metallicity within 1$\sigma$ of literature values.

Relations can reconstruct radial metallicity gradients in the Milky Way.

Tool enables metallicity estimation for Cepheids lacking spectroscopic data.

Abstract

Estimating metallicity of classical Cepheids is of prime importance for studying metallicity effect on stellar evolution, chemical evolution of galaxies, and ultimately its impact on period-luminosity relation used in the extragalactic distance scale. We aim at establishing new empirical relations for estimating the iron content of classical Cepheids for short and long-periods based on Fourier parameters from the $V$-band light curves. We calibrate new interrelations of Fourier parameters to convert $V$-band empirical relations into the $I$-band. Then we apply these relation in $V$ and $I$-bands to Cepheids from Milky Way (MW), Small and Large Magellanic Clouds (SMC and LMC) available in the literature. Last, we map the metallicity distribution in these galaxies for investigating potential application in galactic archeology. These empirical relations in $V$ and $I$ bands are able to derive the mean metallicity of a sample of MW, SMC and LMC Cepheids in agreement with literature values within 1$\sigma$. We also show that these relations are precise enough to reconstruct the radial metallicity gradients within the MW from OGLE data. The empirical relations in the $V$ and $I$ bands calibrated in this paper for short and long-period Cepheids provide a new useful tool to estimate the metallicity of Cepheids which are not accessible by spectroscopy. The calibration can be improved with further high-resolution spectroscopic observations of metal-poor Cepheids and homogeneous photometries in $V$ and $I$ bands.