Time series observations of a single dithered field centered on the diffuse dwarf satellite galaxy Crater II were obtained with the Dark Energy Camera ( DECam ) at the 4m Blanco Telescope at Cerro Tololo Inter-American Observatory , Chile , uniformly covering up to two half-light radii .
Analysis of the g and i time series results in the identification and characterization of 130 periodic variable stars , including 98 RR Lyrae stars , 7 anomalous Cepheids , and 1 SX Phoenicis star belonging to the Crater II population , and 24 foreground variables of different types .
Using the large number of ab-type RR Lyrae stars present in the galaxy , we obtained a distance modulus to Crater II of ( m - M ) _ { 0 } = 20.333 \pm 0.004 ( stat ) \pm 0.07 ( sys ) .
The distribution of the RR Lyrae stars suggests an elliptical shape for Crater II , with an ellipticity of 0.24 and a position angle of 153 \degr .
From the RR Lyrae stars we infer a small metallicity dispersion for the old population of Crater II of only 0.17 dex .
There are hints that the most metal-poor stars in that narrow distribution have a wider distribution across the galaxy , while the slightly more metal rich part of the population is more centrally concentrated .
Given the features in the color-magnitude diagram of Crater II , the anomalous Cepheids in this galaxy must have formed through a binary evolution channel of an old population .