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 \pm 0.011 and \langle P _ { \mathrm { c } } \rangle = 0.359 \pm 0.025 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 \umu = 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 .