The different paths of disk dispersal and evolution: A Herschel view of two regions

Cluster studies reveal that signs of disk evolution (inner holes or gaps, grain growth, small-dust depletion, low accretion rates) are common, even in regions with young ages. First Spitzer, and now also Herschel, combined with ground-based observations, show that not all disks follow the same evolutionary paths, suggesting an interplay of different effects in disk dispersal. In particular, the different properties of transition disks (presence of accretion, radial variations of disk properties, global dust mass) can give valuable information to the processes acting on disk dispersal. The differences in the typical disk structures observed from region to region also suggest that the system's initial conditions and environment probably play an important role and that initial interactions and crowdedness could also affect the disk properties. We present multiwavelength data, including new Herschel/PACS observations, of two very different regions, the young, sparse Coronet cluster, and the older, more populous Cep OB2 region, with the clusters Tr37 and NGC7160. The new Herschel data helps to constrain disk masses and global properties, while our previous Spitzer and ground-based observations, including optical photometry and spectroscopy, provide us information on the presence of gas accretion. Individual disks range from evolved-looking objects in young regions, to the rare long-surviving disks that continue to accrete after 10 Myr. Processes like dust growth/setting/depletion and the opening of inner holes appear to be relatively independent: most dust-depleted/settled disks do not have inner holes, and most disks with inner holes do not have low dust masses. Accretion termination and dust evolution are strongly correlated, but objects with very low accretion rates are rare, which could be consistent with photoevaporation. The diversity in structure and accretion behavior of individual disks shows us the different ways disk dispersal can operate, and what consequences this may have for the outcome of protoplanetary disk evolution.