Hertzsprung–Russell diagram showing pulsating stars (left panel) and rotationally modulated stars (right-hand panel). The dashed line shows the zero-age main sequence, dash-dotted lines show the evolutionary tracks for stars with different masses, all taken from Murphy et al. (2019). The blue and red continuous lines show the empirical boundaries of the instability strip determined by Murphy et al. (2019). The shaded area enclosed by the dotted lines shows the GDOR instability region, following Dupret et al. (2005). The grey dots show all stars including non-variable stars in our sample.