Mass vs. diameter diagram for the sources in Vela-C. Red filled circles and red open circles are prestellar and unbound sources, respectively. Blue filled circles are protostellar sources. Dotted lines are the loci of sources with M = 0.5   M_BE, for T = 8 K and T = 20 K, while the dashed vertical line represents the spatial resolution limit. We also show the curve representing the relation between mass and diameter in the case λ₀ = 160   μm. This relation shifts towards higher masses with increasing λ₀: hence, since all our sources are located below the reported curve, they have optically thin emission at λ > 160   μm.