A morphological diagnostic for dynamical evolution of Wolf-Rayet bubbles

We have observed H alpha and [O III] emission from eight of the most well-d efined Wolf-Rayet ring nebulae in the Galaxy. We find that in many cases th e outermost edge of the [O III] emission leads the H alpha emission. We sug gest that these offsets, when present, are due to the shock from the Wolf-R ayet bubble expanding into the circumstellar envelope. Thus, the details of the WR bubble morphology at Ha and [O III] can then be used to understand better the physical condition and evolutionary stage of the nebulae around Wolf-Rayet stars, as well as to place constraints on the nature of the stel lar progenitor and its mass-loss history.