of the H$\alpha$ loop (or “break-out” feature), causing a noticeable s-shaped distortion in the surface of the larger shell. The H$\alpha$ emission in the limb of the Group I shell is clearly enhanced in the region to the north and south of the H$\alpha$ loop. An effect of the expansion of these shells into one another may have been to weaken the surface of the Group I shell, such that the fast wind from MS11 was able to punch a hole in its wall. Interestingly, there is a gap between the shells. Therefore, if the shells are interacting this would imply they are radiation bounded, and the outer layers of the shells are likely neutral.

In Figure 1d we see, for ob33wr3 and ob33wr2, another interesting case of potentially interacting shells, and the effects of WR winds. A large arc of emission south-west of ob33wr3 is impinging upon a shell structure containing ob33wr2. Interestingly, the Group Ib shell is centered within this arc. As above, the gap between the shell and this arc could indicate the shell is radiation bounded, with neutral material in between. The possibility of a neutral outer layer is strengthened by the evidence for a dust 