Star ISM interaction
Star-ISM interaction
Stars interact with the interstellar medium in many different ways. They interact through energetic UV photons that heat and ionize gas and dust. The heated dust then reemits this energy at longer wavelengths where it is observed with infrared instruments. The interfaces where this energy transfer is important are called Photo-Dissociation Regions or PDRs. The energy input from the star creates a rich chemistry in these regions and numerical models of have been developed (eg. the Meudon PDR code) that can determine the physical parameters (density, temperature, ionization fraction) and the chemical composition.
Benchmarking PDR models in the horsehead nebula
The Horsehead WHISPER project aims to benchmark PDR models on the Horsehead Nebula. This source is an ideal case because the geometry is simple : almost 1D, viewed edge-on, and the density profile is well constrained. The combination of small distance to Earth (at 400 pc, 1” corresponds to 0.002 pc), low illumination (χ = 60) and high density (nH ∼ 105 cm−3) implies that all the interesting physical and chemical processes can be probed in a field-of-view of less than 50” (with typical spatial scales ranging between 1” and 10”).
The interaction of the AE Aur runaway star with the Flaming Star Nebula (IC405)
The runaway star AE Aur (HD34078) is a young bright hot (30 000K) O type star that was ejected 2.5 millions years ago from the Trapezium cluster in Orion. It is now traveling at 120km/s and is illuminating a diffuse cloud of gas and dust to form the Flaming Star Nebula (IC405). Through ionization effects, the gas is compressed to numerous globules that are observable in CO.