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In this paper we make predictions for the behaviour of wind bubbles aroundyoung massive stars using analytic theory. We do this in order to determine whythere is a discrepancy between theoretical models that predict that windsshould play a secondary role to photoionisation in the dynamics of HII regions,and observations of young HII regions that seem to suggest a driving role forwinds. In particular, regions such as M42 in Orion have neutral hydrogenshells, suggesting that the ionising radiation is trapped closer to the star.We first derive formulae for wind bubble evolution in non-uniform densityfields, focusing on singular isothermal sphere density fields with a power lawindex of -2. We find that a classical "Weaver"-like expansion velocity becomesconstant in such a density distribution. We then calculate the structure of thephotoionised shell around such wind bubbles, and determine at what point themass in the shell cannot absorb all of the ionising photons emitted by thestar, causing an "overflow" of ionising radiation. We also estimateperturbations from cooling, gravity, magnetic fields and instabilities, all ofwhich we argue are secondary effects for the conditions studied here. Ourwind-driven model provides a consistent explanation for the behaviour of M42 towithin the errors given by observational studies. We find that in relativelydenser molecular cloud environments \around single young stellar sources,champagne flows are unlikely until the wind shell breaks up due to turbulenceor clumping in the cloud.

Bottling the Champagne: Dynamics and Radiation Trapping of Wind-Driven Bubbles around Massive Stars