  We use multi-frequency radiation hydrodynamics (rad-HD) to simulate radiative
acceleration of a spherically symmetric stellar wind. We demonstrate the rad-HD
capabilities of Athena++ for a series of test problems with multi-group
radiation transfer. We then model the radiative transfer of a single spectral
line through a spherically symmetric, isothermal, "CAK"-type line driven wind.
We find that correctly accounting for the Doppler shift of the absorbed
radiation, the force is well described by the analytic Sobolev line transfer in
the supersonic parts of the solution where the flow is stationary and the
effects of Abbott waves is negligible. Unlike in the analytic, steady-state
solution re-radiation is important and leads to non-trivial radiation energy
density and fluxes in the outer parts of the wind. We discuss a variety of
applications to these multi-group methods that are currently computationally
tractable.
