Dr. Curt Struck, Iowa State

Beautiful bow-shaped mid-infrared emission regions have been discovered in satellite observations of many 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. Such models appear to 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. The heated gas transfers energy into interstellar dust grains, which radiate it. This process, in addition to grain photo-heating, provides an important part of the energy for the emission. The theory suggests that the IR emission process is limited to cases of moderate stellar peculiar velocities, evidently in accord with the observations.