Transitional Disks, Planet Formation, and ALMA Observation
Transitional disks are protoplanetary disks around young stars which are optically thick and gas-rich, but which have AU-scale radial gaps or central clearings in their dust distribution. We will introduce the newest largest sample of transitional disks, which are found by homogenous selection criteria, at 1-3 Myr old star-forming regions: NGC1333, Orion A, Taurus, Chamaeleon, and Ophiuchus. We will demonstrate statistical trends between stellar and disk properties of transitional disks which support the giant planet formation as the origin of gaps and holes in transitional disks. Therefore, transitional disks are important sources to understand a process of planet formation at very early stage and evolution from dusty disks to planetary systems. We will discuss how we can use ALMA to observe transitional disks and what we can expect from the future observation.