CMD of the open cluster NGC 6633 from GDR2. The displayed isochrones are for metallicity Z = 0.012, log(t/yr) = 8.85, (m − M)₀ = 7.841, and A_V = 0.451 mag. The red line represents the non-rotating case, and the two cyan lines are for rotating isochrones with the same ω_i = 0.80, and inclination angles i = 0° (solid line) and i = 90° (dashed line). The green line is the isochrone obtained with PARSEC V1.2S assuming the same parameters of the previous non-rotating case.