Massive young star clusters contain dozens or hundreds of massive stars that inject mechanical energy in the form of winds and supernova explosions, producing an outflow which expands into their surrounding medium, shocking it and forming structures
called superbubbles. The regions of shocked material can have temperatures in excess of 10$^6$ K, and emit mainly in thermal X-rays (soft and hard). This X-ray emission is strongly affected by the action of thermal conduction, as well as by the metallicity of the material injected by the massive stars. We present three-dimensional numerical simulations exploring these two effects, metallicity of the stellar winds and supernova explosions, as well as thermal conduction.
We present new H$alpha$ and H$beta$ images of the HH~1/2 system, and we find that the H$alpha$/H$beta$ ratio has high values in ridges along the leading edges of the HH~1 bow shock and of the brighter condensations of HH~2. These ridges have H$alpha$
/H$beta=4to 6$, which is consistent with collisional excitation from the $n=1$ to the $n=3$ and 4 levels of hydrogen in a gas of temperatures $T=1.5to 10times 10^4$~K. This is therefore the first direct proof that the collisional excitation/ionization region of hydrogen right behind Herbig-Haro shock fronts is detected.
