Mass–age plane for the Antennae clusters. This is an alternative, but equivalent, representation of the data plotted in Figure 1. The lines in the two diagrams are also equivalent: the dashed horizontal one indicates M = 2 × 10 ⁵ M _☉, while the solid diagonal one indicates L = 3 × 10 ⁵ L _☉, the approximate upper limit for stellar contamination. The vertical gap in the data points just above τ = 1 × 10 ⁷ yr is an artifact caused by loops in the color tracks of stellar population models during the RSG phase (see the text).