(V−I),V colour-magnitude diagram from our photometry. The location of RR0 (red filled circles), RR1 (green filled triangles), RR01 (blue inverted triangles), and SX Phe (open green triangles) stars are shown. The variable V53 (unknown type) is shown as an open green square. Typical error bars are shown for different magnitude levels on the right-hand side of the plot. An inset in the top left corner of the plot shows a zoom of the instability strip region of the HB. For added information, isochrones for 9, 10, 11, 12, 13, 14, and 15 Gyr from Dotter et al. (2008) are overplotted in different colours; the best-fit isochrone (13 Gyr) is plotted as a thick green solid line.