Dependence of pulsation mode of Cepheids on metallicity

TL;DR

This study investigates how the pulsation mode of Cepheid variables varies with metallicity across different galaxies, confirming that higher metallicity correlates with a higher ratio of fundamental mode pulsators.

Contribution

It provides new empirical evidence linking Cepheid pulsation modes to metallicity, using extensive data from multiple surveys and refined classification methods.

Findings

The FU/(FU+1O) ratio increases with metallicity across galaxies.

Sample incompleteness does not affect the observed dependence.

The pulsation mode dependence on metallicity is confirmed.

Abstract

The Cepheid variables in SMC, LMC, the Milky Way, M33 and M31 are used to examine the dependence of pulsation mode on metallicity which was previously found in red supergiants. The initial samples of Cepheids are collected from the Cepheid catalogs identified from the OGLE, PS1, DIRECT, WISE and ZTF surveys. The contaminants are removed with the help of the Gaia/EDR3 astrometric information for extra galaxies or by comparing the geometric distance and the distance from the P-L relation for the Milky Way. The division of fundamental and first-overtone mode is refined according to the gap between the two modes in the P-L diagram of the objects in each galaxy. The ratio of FU/(FU+1O) is found to be 0.59, 0.60, 0.69, 0.83 and 0.85 for SMC, LMC, the Milky Way, M33 and M31 respectively in order of metallicity, which confirms that the pulsation mode depends on metallicity in the way that the ratio of FU/(FU+1O) increases with metallicity. This dependence is not changed if the incompleteness of the samples is taken into account.