Wind bubbles within H II regions around slowly moving stars
  Interstellar bubbles around O stars are driven by a combination of the star's
wind and ionizing radiation output. The wind contribution is uncertain because
the boundary between the wind and interstellar medium is difficult to observe.
Mid-infrared observations (e.g., of the H II region RCW 120) show arcs of dust
emission around O stars, contained well within the H II region bubble. These
arcs could indicate the edge of an asymmetric stellar wind bubble, distorted by
density gradients and/or stellar motion. We present two-dimensional,
radiation-hydrodynamics simulations investigating the evolution of wind bubbles
and H II regions around massive stars moving through a dense (n=3000 cm^{-3}),
uniform medium with velocities ranging from 4 to 16 km/s. The H II region
morphology is strongly affected by stellar motion, as expected, but the wind
bubble is also very aspherical from birth, even for the lowest space velocity
considered. Wind bubbles do not fill their H II regions (we find filling
factors of 10-20%), at least for a main sequence star with mass M~30 Msun.
Furthermore, even for supersonic velocities the wind bow shock does not
significantly trap the ionization front. X-ray emission from the wind bubble is
soft, faint, and comes mainly from the turbulent mixing layer between the wind
bubble and the H II region. The wind bubble radiates <1 per cent of its energy
in X-rays; it loses most of its energy by turbulent mixing with cooler
photoionized gas. Comparison of the simulations with the H II region RCW 120
shows that its dynamical age is <=0.4 Myr and that stellar motion <=4 km/s is
allowed, implying that the ionizing source is unlikely to be a runaway star but
more likely formed in situ. The region's youth, and apparent isolation from
other O or B stars, makes it very interesting for studies of massive star
formation and of initial mass functions.
