A Morphological Diagnostic for Dynamical Evolution of Wolf-Rayet Bubbles
  We have observed H-alpha and [OIII] emission from eight of the most well defined Wolf-Rayet ring nebulae in the Galaxy. We find that in many cases the outermost edge of the [OIII] emission leads the H-alpha emission. We suggest that these offsets, when present, are due to the shock from the Wolf-Rayet bubble expanding into the circumstellar envelope. Thus, the details of the WR bubble morphology at H-alpha and [OIII] can then be used to better understand the physical condition and evolutionary stage of the nebulae around Wolf-Rayet stars, as well as place constraints on the nature of the stellar progenitor and its mass loss history. 
Robert A. Gruendl, You-Hua Chu, Bryan C. Dunne and Sean D. Points   (University of Illinois at Urbana-Champaign)