Color-period-diagrams in both Johnson B − V (a) and Gaia (b) colors. Both show our Ru147 stars (green) and those from NGC 6819 (red; Meibom et al. 2015), compared with Ba10 models for three different ages. We only display stars that are neither evolved nor suspected binaries, and only those with periods classified as Category 1 (unambiguous). The rotational isochrones from the Ba10 model are also displayed for ages of 3.0, 2.5, and 1.6 Gyr using blue, gray and yellow corridors respectively. (See text for details.) The central black lines within each corridor correspond to initial period P₀ = 1.1 d for the relevant age.