a) CO J = 2 → 1 emission plotted with the corresponding continuum measurement, the fluxes being normalized at 100 pc. Blue corresponds to CTTS, violet to Herbig, orange to WTTS, red to hybrid and green to debris disks. The open circles mark the binary systems. The Pearson coefficient of correlation of the data, P_c, is indicated in the lower right-hand corner. b) As for Fig. 7a but for the CO J = 3 → 2/0.8 mm emission.