The role of wind driving in OB star bow nebulae
  Bow-shaped mid-infrared emission regions have been discovered in satellite
observations of numerous late-type O and early-type B stars with moderate
velocities relative to the ambient interstellar medium. Previously,
hydrodynamical bow shock models have been used to study this emission. It
appears that such models are incomplete in that they neglect kinetic effects
associated with long mean free paths of stellar wind particles, and the
complexity of Weibel instability fronts. Wind ions are scattered in the Weibel
instability and mix with the interstellar gas. However, they do not lose their
momentum and most ultimately diffuse further into the ambient gas like cosmic
rays, and share their energy and momentum. Lacking other coolants, the heated
gas transfers energy to interstellar dust grains, which radiate it. This
process, in addition to grain photo-heating, provides the energy for the
emission. A weak R-type ionization front, formed well outside the infrared
emission region, generally moderates the interstellar gas flow into the
emission region. The theory suggests that the infrared emission process is
limited to cases of moderate stellar peculiar velocities, evidently in accord
with the observations.
