Properties of M31. II: A Cepheid disk sample derived from the first year of PS1 PAndromeda data

TL;DR

This paper presents a large, newly identified sample of Cepheid variable stars in M31 from the PS1 survey, analyzing their distribution, properties, and period-luminosity relation to enhance understanding of M31's stellar populations.

Contribution

The study provides the largest catalog of Cepheids in M31, introduces an automatic classification method, and analyzes their spatial and age distribution along with the period-luminosity relation.

Findings

Identified 2009 Cepheids, the largest sample in M31 to date.

Population I Cepheids follow the dust pattern in M31's disk.

Detected a curvature in the period-luminosity relation.

Abstract

We present a sample of Cepheid variable stars towards M31 based on the first year of regular M31 observations of the PS1 survey in the r_P1 and i_P1 filters. We describe the selection procedure for Cepheid variable stars from the overall variable source sample and develop an automatic classification scheme using Fourier decomposition and the location of the instability strip. We find 1440 fundamental mode (classical \delta) Cep stars, 126 Cepheids in the first overtone mode, and 147 belonging to the Population II types. 296 Cepheids could not be assigned to one of these classes and 354 Cepheids were found in other surveys. These 2009 Cepheids constitute the largest Cepheid sample in M31 known so far and the full catalog is presented in this paper. We briefly describe the properties of our sample in its spatial distribution throughout the M31 galaxy, in its age properties, and we derive an apparent period-luminosity relation (PLR) in our two bands. The Population I Cepheids nicely follow the dust pattern of the M31 disk, whereas the 147 Type II Cepheids are distributed throughout the halo of M31. We outline the time evolution of the star formation in the major ring found previously and find an age gradient. A comparison of our PLR to previous results indicates a curvature term in the PLR.