Age spread test. Top, from left to right: the open histograms represent the age distribution simulated for a sample of stars of mean age of 2.2 Myr, assuming an observational uncertainty on the luminosity of σ(log L) = 0.10 and intrinsic age spreads of 1, 1.5, 2, 1.5, 3, 1.5, and 4 Myr, respectively. The KS test probability that the two distributions are drawn from the same parent function is also given. Bottom: cumulative functions for each simulation. We use the same legend as in Fig. 10.