During their short existence lasting only few million years, massive stars (more massive than 8 solar masses with spectral type O and B-early) strongly affect the surrounding environment thanks to their intense UV radiation and stellar winds. A single O star, in fact, can loose about 10-6 solar masses of gas in a wind reaching velocities of 1600–2500 km s−1 (Stevens & Hartwell, 2003).
Stars in several star forming regions are observed with a spread in age. This support the idea that star formation is a “slow” process which can propagate across a molecular cloud over million of years (as suggested, for instance, by the Palla & Stahler 2000 study), while several authors have instead suggested that star formation is a “fast” process (e.g.
The study of star-forming regions of our Galaxy is one of the main research topic of the Astronomical Observatory of Palermo. This because they can provide crucial information on how large molecular clouds collapse and form stars, on the early stellar evolutionary stages, on the formation of planetary systems, the formation and dispersion of protoplanetary disks, and the history and
