Line-driven ablation and wind tilting by external irradiation

The directional variation of the velocity gradient in a supersonic, radiati vely accelerated flow gives an effectively anisotropic character to the lin e-scattering process. This leads to surprising consequences in source geome tries that are more complex than isolated nonrotating stars. In this paper we explore the wind dynamics from a planar slab atmosphere that is irradiat ed by an external oblique source, within the framework of standard Castor, Abbott, & Klein (CAK) wind theory. We show that the presence of externally incident radiation can be surprisingly effective at tilting the how away fr om the vertical. Even more surprising is our conclusion that such illuminat ion should often enhance the mass loss and can even induce outflow from a s urface with no intrinsic radiation source. We examine the physical causes o f such "line-driven ablation" and discuss the potential implications for mo deling line-driven flows in massive-star binary and accretion-disk systems.