CMD showing the positions of our cluster variable sources, separated into four panels by variability class: pulsational, solar-like oscillators, binaries, and rotational variables. High-probability NGC 6819 members (P  >  0.9) are overplotted as gray boxes. The solid curve is a 2.5 Gyr MIST isochrone with [Fe/H] = +0.05 dex (J. Choi et al. 2016). We annotate the top of the figure to indicate the range of spectral types, adding shaded panels that correspond to the hexadecimal color codes for a given spectral type (corresponding to luminosity class V and subclass 5), as reported by J.-V. Harre & R. Heller (2021).