Halting planet migration by photoevaporation from the central source

The recent discovery of Jupiter-mass planets orbiting at a few AU from their stars compliments earlier detections of massive planets on very small orbits. The short period orbits strongly suggest that planet migration has occurred, with the likely mechanism being tidal interactions between the planets and the gas disks out of which they formed. The newly discovered long period planets, together with the gas giant planets in our solar system, show that migration is either absent or rapidly halted in at least some systems. We propose a mechanism for halting type-II migration at several AU in a gas disk. Photoevaporation of the disk by irradiation from the central star can produce a gap in the disk at a few AU, preventing planets outside the gap from migrating down to the star. This would result in an excess of systems with planets at or just outside the photoevaporation radius. Subject headings: accretion, accretion disks—planetary systems: formation— planetary systems: protoplanetary disks—planets and satellites: formation— solar system: formation Department of Astronomy and Astrophysics,University of Toronto, Toronto, ON M5S 3H8, Canada; [email protected] National Research Council Canada, Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada; [email protected] Canadian Institute for Theoretical Astrophysics, University of Toronto, Toronto, ON M5S 3H8, Canada; [email protected] Canada Research Chair in Astrophysics