Luminosity–age plane for the Antennae clusters. The luminosities are in the V band and have been corrected for extinction. The dashed diagonal line is the evolutionary track of a model cluster with an initial mass of M = 2 × 10 ⁵ M _☉ (Bruzual & Charlot 2003), while the solid horizontal line at L = 3 × 10 ⁵ L _☉ is 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).