Abstract
Ultracompact HII regions are in a regime of approximate pressure balance with the surrounding, dense molecular clouds. In this paper, we apply a newly developed ``thick shell'' formalism to the case of an expanding HII region energized by both the photoionizing radiation and the wind from the central stellar source. The resulting model leads to analytic and quasi-analytic solutions that have a transition to a regime (absent in the classical ``wind-driven bubble'' analytic solutions) in which the hot, stellar wind bubble expands quasi-statically, in approximate pressure equilibrium with the surrounding ISM. This regime is relevant for the observed ultracompact HII regions. We present the time-evolution of the radius and the thickness of the expanding HII shell for different values of a single, dimensionless parameter that determines the characteristics of the solution.
