Fundamentalization of periods for first and second-overtone classical Cepheids

TL;DR

This paper develops updated empirical relations to convert higher-overtone Cepheid periods to fundamental mode periods, considering metallicity effects, to improve astrophysical analyses involving these variable stars.

Contribution

It provides modern, high-quality fundamentalization relations for first- and second-overtone Cepheids across a wide period range, incorporating metallicity dependence.

Findings

Relations are applicable over a broad period range.

Metallicity influences the fundamentalization relations.

Comparison with extragalactic Cepheids reveals metallicity variations.

Abstract

Almost half of all classical Cepheids do not pulsate in fundamental mode, and nowadays, the fundamentalization of their higher-mode periods is frequently applied to increase the sample size in astrophysical investigations and allow for comparison with fundamental-mode Cepheids. On the other hand, the relations used to obtain fundamentalized periods are either old or based on small samples that cover narrow period ranges. We used available data of 989 Cepheids pulsating in at least two modes to obtain modern, high-quality empirical fundamentalization relations applicable in a wide range of periods of first- and second-overtone Cepheids for metallicities typical for the Milky Way and Magellanic Clouds. A clear correlation between the features of these relations and metallicity is seen, and periods with lower sensitivity to metallicity are identified. We also compare our results with double-mode Cepheids from the M31 and M33 galaxies. For the first galaxy, this indicates Cepheids have metallicities from supersolar to typical for the LMC, while for the latter, from solar to typical for the SMC. A general discussion of the usage of a different type of fundamentalization relations depending on the scientific problem is included.