SIMBAD references

Embedded clusters usually contain young stellar objects in different evolutionary stages. We investigate number ratios of objects in these classes in the star-forming regions ρ Ophiuchi, Serpens, Taurus, Chamaeleon I, NGC 7129, IC 1396A and IC 348. They are compared to the temporal evolution of young stars in numerical simulations of gravoturbulent fragmentation in order to constrain the models and to determine the evolutionary stage of the clusters. Serpens is the youngest and IC 348 the most evolved cluster, although the time when the observations are best represented by the models varies strongly depending on the model. We find an inverse correlation of the star formation efficiency (SFE) of the models with the Mach number. However, the observational SFE values cannot be reproduced by the current isothermal models. This argues for models that take into account protostellar feedback processes and/or the effects of magnetic fields.