Properties of M31. III: Candidate Beat Cepheids from PS1 PAndromeda Data and Their Implication on Metallicity Gradient

TL;DR

This study identifies 17 beat Cepheids in M31 using Pan-STARRS data, deriving their metallicity and metallicity gradient, which aligns more closely with planetary nebulae than HII region measurements.

Contribution

The paper presents the first analysis of beat Cepheids in M31 to estimate metallicity and its gradient, providing new insights into the galaxy's chemical composition.

Findings

Metallicity within 15 kpc is subsolar.

Metallicity gradient aligns with planetary nebulae data.

Identified 17 beat Cepheids in M31.

Abstract

We present a sample of M31 beat Cepheids from the Pan-STARRS 1 PAndromeda campaign. By analyzing three years of PAndromeda data, we identify seventeen beat Cepheids, spreading from a galactocentric distance of 10 to 16 kpc. Since the relation between fundamental mode period and the ratio of fundamental to the first overtone period puts a tight constraint on metallicity we are able to derive the metallicity at the position of the beat Cepheids using the relations from the model of Buchler (2008). Our metallicity estimates show subsolar values within 15 kpc, similar to the metallicities from HII regions (Zurita & Bresolin 2012). We then use the metallicity estimates to calculate the metallicity gradient of the M31 disk, which we find to be closer to the metallicity gradient derived from planetary nebulae (Kwitter et al. 2012) than the metallicity gradient from HII regions (Zurita & Bresolin 2012).