Absolute I-magnitude versus intrinsic I − K for GES targets in the open clusters NGC 2516, NGC 2547 and NGC 2264 using the cluster parameters shown in Table 2. Points show all GES targets (with spectra that have S/N> 5). Black crosses show stars with reported periods that are cluster members based on their RV (see Sect. 2.3) with v sin i> 5 km s^-1, red triangles show other GES targets with reported periods. Lines show solar metallicity model isochrones interpolated to the cluster age for different evolutionary models, see Sect. 4.1, solid line – BHAC15 (Baraffe et al. 2015), blue dotted line – Dartmouth (Dotter et al. 2008), blue dashed line – , Dartmouth modified for magnetic fields (Feiden & Chaboyer 2013).