THE HII REGIONS AND BOW SHOCKS AROUND RUNAWAY O STARS

Abstract

We present a model for the HII region and stellar wind bow shock formed by runaway O stars passing through the Galactic disk. We develop a quasi-analytic approach in which the absorption of stellar ionizing photons by the bow shock is considered. With these models we study the transition between a detached ionization front (leading the bow shock) and an ionization front trapped by the stellar wind bow shock. We find that for an O7 star one needs to have a stellar velocity of only a few km/s and an environmental density > 105 cm−3.