r_I − Hα vs. r_I − i two-colour diagram for variable sources. The stars in the upper panel are coloured according to the logarithm of the distance from Gaia DR2 (Bailer-Jones et al. 2018). The solid red line is the unreddened MS, while the dashed red line is the reddening line for an A2V star up to A_V = 10. The blue line is the unreddened sequence for the giants. Lower panel: density plot of the stars identified as variables. Evidently, the great majority are located in the main stellar locus at r_I − i ≲ 1. The other notable feature is the “island” of relatively extreme red giants beginning at r_I − i ∼ 2.5.