  Dust waves and bow waves result from the action of a star's radiation
pressure on a stream of dusty plasma that flows past it. They are an
alternative mechanism to hydrodynamic bow shocks for explaining the curved arcs
of infrared emission seen around some stars. When gas and grains are perfectly
coupled, for a broad class of stellar parameters, wind-supported bow shocks
predominate when the ambient density is below 100 per cubic cm. At higher
densities radiation-supported bows can form, tending to be optically thin bow
waves around B stars, or optically thick bow shocks around early O stars. For
OB stars with particularly weak stellar winds, radiation-supported bows become
more prevalent.
