Global Protoplanetary Disk Evolution and Clumpy Star Formation in the Cephei OB2 Region

The Herschel/PACS view of the Cep OB2 region: Global protoplanetary disk evolution and clumpy star formation

Authors:

Sicilia-Aguilar et al

Abstract:

We use Herschel PACS observations at 70 and 160μm to probe the protoplanetary disks around young stars in the CepOB2 clusters Tr37 and NGC7160 and to trace the small-scale cloud structure. We detect 95 protoplanetary disks at 70μm, 41 at 160μm, and obtain upper limits for over 130 objects. The detection fraction at 70μm depends on the spectral type (88% for K4 or earlier, 17% for M3 or later stars) and on the disk type (∼50% for full and pre-transitional disks, ∼35% for transitional disks, no low-excess/depleted disks detected). Non-accreting disks are consistent with significantly lower masses. Accreting transition and pre-transition disks have higher 70μm excesses than full disks, suggestive of more massive, flared and/or thicker disks. Herschel data also reveal several mini-clusters in Tr37, small, compact structures containing a few young stars surrounded by nebulosity. Far-IR data are an excellent probe of the evolution of disks that are too faint for submillimetre observations. We find a strong link between far-IR emission and accretion, and between the inner and outer disk structure. Herschel confirms the dichotomy between accreting and non-accreting transition disks. Substantial mass depletion and global evolution need to occur to shut down accretion in a protoplanetary disk, even if the disk has inner holes. Disks likely follow different evolutionary paths: Low disk masses do not imply opening inner holes, and having inner holes does not require low disk masses. The mini-clusters reveal multi-episodic star formation in Tr37. The long survival of mini-clusters suggest that they formed from the fragmentation of the same core. Their various morphologies favour different formation/triggering mechanisms acting within the same cluster. Herschel also unveils what could be the first heavy mass loss episode of the O6.5 star HD206267.