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We consider the Orion Nebula (M 42) within a project aimed at studying the interaction between massive stars and their surrounding ISM. This is an HII region ionized by θ1 Ori C, one of the four massive stars in the Trapezium Cluster. θ1 Ori C has the earliest spectral type (O7Vp) among them, emitting an ionizing flux several orders of magnitude

It is often stated that there is no point in obtaining mid-infrared data with S/N>20, even in the best of cases, because it is impossible to obtain a calibration to better than 5%, although in many cases 10% or greater is a more accurate reflection of the true quality of calibration. Mid-infrared calibration is difficult because of the lack of

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In a recent paper (Crivellari et al., 2003) we summarized the principles of the algorithmic representation of the structure of a stellar atmosphere. We mentioned there our recent progresses in the numerical treatment of both the global method and the basic components of the corresponding models. As the natural sequel to that paper, we wish to

A new scenario is proposed in which the continuous creation of stars results into a highly concentrated massive (globular cluster-like) stellar system. We show that under very general conditions a large-scale gravitational instability in the ISM that triggers the collapse of a massive cloud leads with the aid of newly-formed stars to a standing