The fluxes of the [O i] 63 μm, the [C ii] 158 μm, the CO J = 18−17, and the o-H₂O 179.5 μm lines are plotted versus the source luminosity (upper panel) and their adjacent continuum (lower panel) for all the sources in our sample (black, red, green, and blue dots). For FS Tau A+B and T Tau N+S the plotted source luminosity is a lower limit, since L _∗  of the Class I components FS Tau B and T Tau S is unknown. The upper limit on the stellar luminosity for DG Tau B corresponds to its bolometric luminosity as estimated by Kruger et al. (2011).