The driving of stellar winds from the radiation pressure of hot stars was suggested early in the century, and has since been found to provide a good explanation of mass loss in a wide variety of astronomical objects, ranging from very hot ("O-type") stars, to active galactic nuclei, to quasars. In past NSF supported work the Principal Investigator (PI) has demonstrated fundamental flaws in earlier concepts of radiatively driven winds. For example, it is now clear that scattering of photons in dense winds inhibits the growth of self-induced instabilities so that the winds only develop mild inhomogeneities. However, such instabilities have been observed in both optical and ultraviolet spectral lines and are thought to indicate the presence of colliding winds moving at different speeds. The shocks generated by these collisions may be the primary source of x-rays in objects with radiatively driven winds. With this three-year award the PI and a postdoctoral fellow will develop numerical simulations with more realistic atmospheric models and to extend earlier analytical solutions to two and even three dimensions. This work will assess the role of turbulent instabilities in the evolution of inhomogeneities through the wind flow. It is expected that this work will ultimately have a wide application to extragalactic objects in addition to O stars.
