Stellar Wind Erosion of Protoplanetary Discs

An analytic model is developed for the erosion of protoplanetary gas discs by high velocity magnetized stellar winds. The winds are centrifugally driven from the surface of rapidly rotating, strongly magnetized young stars. The presence of the magnetic field in the wind leads to Reynolds numbers sufficiently large to cause a strongly turbulent wind/disk boundary layer which entrains and carries away the disc gas. The model uses the conservation of mass and momentum in the turbulent boundary layer. The time-scale for significant erosion depends on the disc accretion speed and accretion rate and on the wind mass loss rate and the wind velocity. The time-scale is estimated to be 2E6 yr. A significant contribution to the disc erosion can come from frequent powerful coronal mass ejections (CMEs) where the average mass loss rate in CMEs and velocities have values comparable to those for the steady wind.