Low‐Mass Protoplanet Migration in T Tauri α‐Disks

We present detailed estimates of ''type-I'' migration rates for low-massproto-planets embedded in steady-state T-Tauri alpha-disks, based on Lindbladtorque calculations ignoring feedback on the disk. Differences in migrationrates for several plausible background disk models are explored and we contrastresults obtained using the standard two dimensional formalism of spiral densitywave theory with those obtained from a simple treatment of three-dimensionaleffects. Opacity transitions in the disk result in sudden radial variations ofthe migration rates. Regions with minimal migration rates may be preferredsites of gravitational interactions between proto-planets. Three-dimensionaltorques are significantly weaker than two-dimensional ones and they aresensitive to the surface density profile of the background disk. We find thatmigration times in excess of runaway envelope accretion times or T-Tauri disklifetimes are possible for Earth-mass proto-planets in some background diskmodels, even at sub-AU distances. We conclude that an understanding of thebackground disk structure and ''viscosity'', as well as a proper treatment ofthree-dimensional effects in torque calculations, are necessary to obtainreliable estimates of ``type-I'' migration rates.Comment: Minor revisions, 31 pages, 7 figures, accepted for publication in Ap