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Analytic and numerical models for the expansion of a compact H ii region




‘Compact’ H ii regions (embedded in dense molecular clouds) relax to a pressure equilibrium configuration in shorter time-scales than the main-sequence lifetime of the exciting O stars. This result motivates a rederivation of the analytic model for the expansion of an H ii region into a uniform environment. We have modified the classical model so as to include the breaking of the expansion necessary to reach the correct, final pressure equilibrium configuration. We find that this extended model also has a full analytic solution. A comparison of the analytic solution with a (spherically symmetric) numerical simulation is also presented.