Young stars in star forming regions

We applied the same procedure in a consistent manner to the other regions. Results. In L1688 the relations between dM/dt_acc_ and M*, Mdust and M*, and dM/dt_acc_ Mdust have a roughly linear trend with slopes 1.8-1.9 for the first two relations and ~1 for the third, which is similar to what found in the other regions.

When ordered according to the characteristic age of each region, which ranging from ~0.5 to ~5Myr, dM/dt_acc_ as t^-1^, when corrected for the different stellar mass content; Mdust follows roughly the same trend, ranging between 0.5 and 5Myr, but has an increase of a factor of ~3 at ages of 2-3Myr. We suggest that this could result from an earlier planet formation, followed by collisional fragmentation that temporarily replenishes the millimeter-size grain population.

The dispersion of dM/dt_acc_ and Mdust around the best-fitting relation with M*, as well as that of dM/dt_acc_ Mdust are equally large. When adding all the regions together to increase the statistical significance, we find that the dispersions have continuous distributions with a log-normal shape and similar widths (~0.8dex). This detailed study of L1688 confirms the general picture of Class II/F disk properties and extends it to a younger age.

The amount of dust observed at ~1Myr is not sufficient to assemble the majority of planetary systems, which suggests an earlier formation process for planetary cores. The dust mass traces to a large extent the disk gas mass evolution, even if the ratio Mdust/Mdisk at the earliest age (0.5-1Myr) is not known. Two properties are still not understood: the steep dependence of dM/dt_acc_ Mdust on M* and the cause of the large dispersion in the three relations analyzed in this paper, in particular that of the dM/dt_acc_ Mdust relation.