International Summer Institute for Modeling in Astrophysics

The transitional disks around young stars are protoplanetary disks with inner holes that are relatively empty of small dust grains, as inferred from the excess of far-infrared emission in their spectral energy distribution (SED) (Espaillat et al. 2007,2010). Recently, a new class of 'pre-transitional disks' are identified as exhibiting substantial emission from an optically thick inner disk separated from an optically thick outer disk by an optically thin gap (Espaillat et al. 2010). One plausible model for gap opening in these disks is by multiple giant planets (Zhu et al. 2011). However, two major problems remain to be solved. Firstly, micron-sized dust grains are not removed efficiently enough from the giant planet's gap to explain the observed low disk emission at near/mid-infrared wavelengths. Secondly, the presence of multiple Jupiter mass planets in resonance is not likely in standard disk models. We have developed a simple but robust coagulation-fragmentation model showing that piled-up material at the outer gap edge acts as a very efficient filter for micron-sized grains. Its reduction of the particle flow by two orders of magnitude provides excellent agreement with observational data. We can also produce high local surface density of particles at the outer edge of the gap, which may trigger planet formation in the outer disk.