Abstract
I present simple analytic models for steady-state photoevaporation flows in H II regions. Two cases are considered: (1) the globally open flow from a plane ionization front, where the ionizing source is offset a finite distance from the front; (2) local flows from the crests of ionization-front undulations in a globally closed H II region. I show that the first case can well reproduce the observed geometry and physical properties of the principal optical line-emitting layer in the inner Orion nebula, while the second case can naturally explain the observed ionized density increase in the vicinity of the Orion bar.
