Published online by Cambridge University Press: 12 April 2016
The boundary layer region, where the accretion disk meets the accreting star, is crucial to understanding the spectra and evolution of accretion disk systems. Recent numerical modeling of the flow of the accreting material and radiation in the boundary layer has provided a better understanding of this region. I will describe the “standard” boundary layer structure predicted by the models for the case where the boundary layer is optically thick and geometrically thin in the vertical direction. Large variations in this structure can occur when the boundary layer becomes optically thin or geometrically thick. Boundary layer models have been applied to cataclysmic variables and accreting pre-main-sequence stars. I will discuss the boundary layer spectra predicted by the models and how well they agree with observations of these objects. The boundary layer also controls the transfer of angular momentum and energy between the disk and star. This can have important effects upon pre-main-sequence stellar evolution.