Color–period diagram, showing the variability period as a function of a pseudo-color for our final sample described in Sect. 2. This pseudo-color, denominated c3, is suggested as reddening-free by Catelan et al. (2011) and is computed as described in Sect. 2.6. Circle size represents the variability amplitude in mag and colors indicate the luminosity class. The typical error of c₃ is displayed by the error bar.