L_bol − M diagram for prestellar and protostellar sources in Vela-C (red and blue circles, respectively). Grey solid lines represent the evolutionary tracks for low-mass objects adopted by Molinari et al. (2008), for initial values of 0.5, 1, 5, and 10 M_⊙, respectively. An arrow indicates the evolution direction, while green lines delimit the region of transition between Class 0 and Class I sources (André et al. 2000). The red dotted line represents the best-fitting power law (L_bol ∝ M^{0.42 ± 0.04}) for the distribution of the prestellar sources.