We investigate the scale dependence of fluctuations inside a realistic model of an evolving turbulent HII region and to what extent these may be studied observationally. We find that the multiple scales of energy injection from champagne flows and th
e photoionization of clumps and filaments leads to a flatter spectrum of fluctuations than would be expected from top-down turbulence driven at the largest scales. The traditional structure function approach to the observational study of velocity fluctuations is shown to be incapable of reliably determining the velocity power spectrum of our simulation. We find that a more promising approach is the Velocity Channel Analysis technique of Lazarian & Pogosyan (2000), which, despite being intrinsically limited by thermal broadening, can successfully recover the logarithmic slope of the velocity power spectrum to a precision of +-0.1 from high resolution optical emission line spectroscopy.
We study the evolution of the interstellar and circumstellar media around massive stars (M > 40M_{odot}) from the main sequence through to the Wolf-Rayet stage by means of radiationhydrodynamic simulations. We use publicly available stellar evolution
models to investigate the different possible structures that can form in the stellar wind bubbles around Wolf-Rayet stars. We find significant differences between models with and without stellar rotation, and between models from different authors. More specifically, we find that the main ingredients in the formation of structures in the Wolf-Rayet wind bubbles are the duration of the Red Supergiant (or Luminous Blue Variable) phase, the amount of mass lost, and the wind velocity during this phase, in agreement with previous authors. Thermal conduction is also included in our models. We find that main-sequence bubbles with thermal conduction are slightly smaller, due to extra cooling which reduces the pressure in the hot, shocked bubble, but that thermal conduction does not appear to significantly influence the formation of structures in post-main-sequence bubbles. Finally, we study the predicted X-ray emission from the models and compare our results with observations of the Wolf-Rayet bubbles S,308, NGC,6888, and RCW,58. We find that bubbles composed primarily of clumps have reduced X-ray luminosity and very soft spectra, while bubbles with shells correspond more closely to observations.
