BOUNDARY-LAYERS IN PRE-MAIN-SEQUENCE ACCRETION DISKS

We present self-consistent solutions, using alpha-viscosity, for the flow and energetics of optically thick boundary layers in accretion disks around pre-main-sequence stars. The solutions span a range of accretion rates from M = 10(-7) to 10(-4) M. yr-1 and are in qualitative agreement with observations of T Tauri and FU Orionis stars. The boundary layers in the solutions have two radial zones. The viscous dissipation occurs in a relatively narrow dynamical boundary layer, but most of the energy is actually radiated over a wider thermal boundary layer which extends to larger radii. We find that at low accretion rates, the boundary layer emission is clearly visible as a separate hot component in the combined spectrum of the disk and boundary layer, but this component is more difficult to distinguish at higher accretion rates.