The pulsating variable star population in DDO210

TL;DR

This study identifies and characterizes pulsating variable stars in the dwarf galaxy DDO210, revealing its stellar populations, metallicity, distance, and recent star formation activity through analysis of RR Lyrae and Cepheid variables.

Contribution

First detailed analysis of pulsating variable stars in DDO210, providing insights into its stellar populations, metallicity, and star formation history using HST data.

Findings

32 RR Lyrae stars identified, indicating ancient stellar population.

75 Cepheid variables found, mostly short-period classical Cepheids.

Distance modulus of 25.07 determined, consistent with other estimates.

Abstract

We have probed the pulsating variable star content of the isolated Local Group dwarf galaxy, DDO210 (Aquarius), using archival Advanced Camera for Surveys/$Hubble$ $Space$ $Telescope$ imaging in the F475W and F814W passbands. We find a total of 32 RR Lyrae stars (24 ab-type, 8 c-type) and 75 Cepheid variables. The mean periods of the ab-type and c-type RR Lyrae stars are calculated to be $\langle$P$_{\mathrm{ab}}\rangle = 0.609\pm0.011$ and $\langle$P$_{\mathrm{c}}\rangle = 0.359\pm0.025$ days, respectively. The light curve properties of the fundamental mode RR Lyrae stars yield a mean metallicity of $\langle$[Fe/H]$\rangle$ = -1.63$\pm$0.11 dex for this ancient population, consistent with a recent synthetic colour-magnitude diagram analysis. We find this galaxy to be Oosterhoff-intermediate and lacking in high-amplitude, short-period ab-type RR Lyrae, consistent with behavior recently observed for many dwarf spheroidals and ultra-faint dwarfs in the Local Group. We find a distance modulus of $\mu = 25.07\pm 0.12$ as determined by the RR Lyrae stars, slightly larger but agreeing with recent distance estimates from the red giant branch tip. We also find a sizable population of Cepheid variables in this galaxy. We provide evidence in favor of most if not all of these stars being short-period classical Cepheids. Assuming all of these stars to be classical Cepheids, we find that most of these Cepheids are $\sim$300 Myr old, with the youngest Cepheids being offset from the older Cepheids and the centre of the galaxy. We conclude that this may have resulted from a migration of star formation in DDO210.