The protoplanetary disk population in the ρ-Ophiuchi region L1688 and the time evolution of Class II YSOs

doi:10.1051/0004-6361/202141380

The protoplanetary disk population in the ρ-Ophiuchi region L1688 and the time evolution of Class II YSOs

Context. Planets form during the first few Myr of the evolution of the star-disk system, possibly before the end of the embedded phase. The properties of very young disks and their subsequent evolution reflect the presence and properties of their planetary content.
Aims: We present a study of the Class II/F disk population in L1688, the densest and youngest region of star formation in Ophiuchus. We also compare it to other well-known nearby regions of different ages, namely Lupus, Chamaeleon I, Corona Australis, Taurus and Upper Scorpius.
Methods: We selected our L1688 sample using a combination of criteria (available ALMA data, Gaia membership, and optical and near-IR spectroscopy) to determine the stellar and disk properties, specifically stellar mass (M_⋆), average population age, mass accretion rate (Ṁ_acc) and disk dust mass (Ṁ_dust). We applied the same procedure in a consistent manner to the other regions.
Results: In L1688 the relations between Ṁ_acc and M_⋆, M_dust and M_⋆, and Ṁ_acc and M_dust 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 ~5 Myr, Ṁ_acc decreases as t⁻¹, when corrected for the different stellar mass content; M_dust follows roughly the same trend, ranging between 0.5 and 5 Myr, but has an increase of a factor of ~3 at ages of 2-3 Myr. 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 Ṁ_acc and M_dust around the best-fitting relation with M_⋆, as well as that of Ṁ_acc versus M_dust 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 (~0.8 dex).
Conclusions: 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 ~1 Myr 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 M_dust/M_disk at the earliest age (0.5-1 Myr) is not known. Two properties are still not understood: the steep dependence of Ṁ_acc and M_dust on M_⋆ and the cause of the large dispersion in the three relations analyzed in this paper, in particular that of the Ṁ_acc versus M_dust relation.