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We present the first detailed study of the RR Lyrae variable population inthe Local Group dSph/dIrr transition galaxy, Phoenix, using previously obtainedHST/WFPC2 observations of the galaxy. We utilize template light curve fittingroutines to obtain best fit light curves for RR Lyrae variables in Phoenix. Ourtechnique has identified 78 highly probable RR Lyrae stars (54 ab-type; 24c-type) with about 40 additional candidates. We find mean periods for the twopopulations of $\langle P_{ab}\rangle = 0.60 \pm 0.03$ days and $\langleP_{c}\rangle = 0.353 \pm 0.002$ days. We use the properties of these lightcurves to extract, among other things, a metallicity distribution function forab-type RR Lyrae. Our analysis yields a mean metallicity of $\langle[Fe/H]\rangle = -1.68 \pm 0.06$ dex for the RRab stars. From the mean periodand metallicity calculated from the ab-type RR Lyrae, we conclude that Phoenixis more likely of intermediate Oosterhoff type; however the morphology of theBailey diagram for Phoenix RR Lyraes appears similar to that of an Oosterhofftype I system. Using the RRab stars, we also study the chemical enrichment lawfor Phoenix. We find that our metallicity distribution is reasonably wellfitted by a closed-box model. The parameters of this model are compatible withthe findings of Hidalgo et al. (2009) further supporting the idea that Phoenixappears to have been chemically enriched as a closed-box-like system during theearly stage of its formation and evolution.

The RR Lyrae Variable Population in the Phoenix Dwarf Galaxy