An IR Study of the Velocity Structure of the Cometary Compact HII region   G29.96-0.02
  We have mapped the velocity structure of the cometary compact HII region G29.96-0.02 using long-slit echelle spectra of the HI Br gamma line. This technique detects line emission over a much wider area at the necessary spatial resolution compared to radio recombination line observations. Significant structure in both the velocity centroids and the line widths is seen over the entire nebula. Large line widths are seen ahead of the bow and in the tail which may be due to turbulent motions in shocked and interface regions respectively. We construct analytic models of the density and velocity structure in order to attempt to distinguish between the bow shock and champagne flow models which have been put forward to explain the cometary morphology of many compact HII regions. The bow shock model is unable to explain the large velocity gradient that we see right across the tail of the cometary region which can only be explained by the streaming motions towards low density regions in the champagne model. However, our approximation to the champagne model is also not able to fit all of the features of the data. More realistic versions of this model which include the effects of stellar winds and density gradients may be able to provide a better match to these data. 
Stuart Lumsden (AAO) and Melvin Hoare (MPIA)