Abstract

Protoplanetary disks are the birthplaces of plants, but the spatial resolution at long wavelengths has so far been insufficient to resolve the critical 5-30 AU region where they are formed. ALMA now allows us to zoom in to nearby disks and probe the physical and chemical structure associated with planet formation. In this talk, an overview of recent work by our group and colleagues on observations and models of protoplanetary disks around young stars in various stages of evolution will be presented. Early ALMA results include evidence for rotationally supported disks in the deeply embedded stage, the detection of organic molecules (including sugar) and water in forming disks, and the first images of the CO snowline in mature disks. The ALMA data are complemented by VLT -CRIRES, Spitzer and Herschel observations, which reveal new processes in the inner few AU of disks. Special attention will be given to transitional disks, which are a subset of disks with evidence for sharp-rimmed cavities (gaps or holes) in their inner part but with otherwise normal outer disks. These disks are called ‘transitional’ because they are thought to represent the evolutionary phase from the gas-rich protoplanetary disk to the gas-poor debris disk stage. They are the best candidate sources for harbouring young giant planets or where planet formation is currently taking place. The surprising results of our ALMA Cycle 0 program on the discovery of a huge dust trap (a ‘planetesimal or Kuiper-Belt factory’) in one particular transitional disk will be presented.