u- and r-band variability amplitudes observed for WTTS (blue squares) and CTTS (magenta circles) are compared to cool (upper panel) and hot (lower panel) spot model predictions. Model tracks are traced assuming a fixed photospheric temperature Tphot of 4000 K (corresponding to a K7 star). Each model track corresponds to a different spot temperature Tspot: in the upper panel (cool spots), four different Tspot values are considered, ranging from 200 K to 1500 K lower than Tphot; in the lower panel (hot spots), five different Tspot values are explored, ranging from 200 K to 4000 K above the photospheric temperature. Along each track, ℱeq varies from 0.1% to 60%; reference values of the spot-to-star surface ratio are marked with crosses for clarity. For CTTS, two additional subclasses are highlighted: objects dominated by stochastic accretion bursts (Stauffer et al. 2014, orange dots) and objects dominated by circumstellar extinction (McGinnis et al. 2015, green triangles), either quasi-periodic (AA Tau objects) or aperiodic.
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