Variable Stars in the Cetus dSph Galaxy: Population Gradients and Connections with the Star Formation History

TL;DR

This study catalogs 638 variable stars in the Cetus dwarf galaxy, analyzing their properties and spatial distribution to understand the galaxy's star formation history and metallicity gradients.

Contribution

It provides the first comprehensive variable star catalog for Cetus and investigates the presence of metallicity gradients through RR Lyrae properties, revealing no significant gradient.

Findings

Homogeneous RR Lyrae properties across Cetus

Radial gradient in HB and RGB morphologies

Differences in star formation history compared to Tucana

Abstract

We investigate the variable star content of the isolated, Local Group, dwarf spheroidal galaxy (dSph) Cetus. Multi-epoch, wide-field images collected with the VLT/VIMOS camera allowed us to detect 638 variable stars (630 RR Lyrae stars and 8 Anomalous Cepheids), 475 of which are new detections. We present a full catalogue of periods, amplitudes, and mean magnitudes. Motivated by the recent discovery that the pulsational properties of the RR Lyrae stars in the Tucana dSph revealed the presence of a metallicity gradient within the oldest (>10 Gyr old) stellar populations, we investigated the possibility of an analogous effect in Cetus. We found that, despite the obvious radial gradient in the Horizontal Branch (HB) and Red Giant Branch (RGB) morphologies, both becoming bluer on average for increasing distance from the center of Cetus, the properties of the RR Lyrae stars are homogeneous within the investigated area (out to r~15'), with no significant evidence of a radial gradient. We discuss this in connection with the star formation history (SFH) previously derived for the two galaxies. The observed differences between these two systems show that even systems this small show a variety of early evolutionary histories. These differences could be due to different merger or accretion histories.