Kurt Liffmann (CSIRO/MSE)

Accretion Disk Processes: Magnetic Flows, Photo Evaporation and Disk Compression -- Kurt Liffman

Abstract

Recent results from the Spitzer Space Telescope suggest that magnetically powered, protostellar jet flows are reprocessing the disks that surround young stars. Crystalline dust is being formed via outburst radiation close to protostars and ejected away from the protostar at average radial speeds of approximately 40 km/s. These observations are consistent with the Stardust mission that gathered dust from Comet Wild 2, where this dust had been processed at very high temperatures that could only have existed near the proto-Sun.

Stellar radiation also heats the surface of young stellar disks and produces photo-evaporative flows. There is a critical radial distance from the star where the disk surface is subject to photo-evaporation at distances beyond this "critical" or "gravitational" radius. Over time, a gap appears in the accretion disk, so the disk is split in two and becomes a transition disk. It has been observed that the scale height of the inner disk can compress and decompress with time, while the outer disk is subsequently illuminated and shadowed. This lighthouse effect may be due to magnetic compression of the inner disk due to interaction with the stellar magnetosphere. It is shown how this time variable magnetic compression may arise. It is also suggested that a double peaked Pedersen conductivity exists in stellar accretion disks that helps produce disk compression and the outflow/accretion activity.