Since the last ten years it has been recognized that many stars are associated with molecular outflows. These are characterized by the presence, near the star, of high velocity molecular gas seen mainly in the millimeter lines of 12CO. The CO spectra observed near such stars present the usual gaussian shape plus high velocity emission, generally faint. The observed velocities may amount to 100 km/s, much larger than the escape velocities. These high velocity wings are also seen in other molecules such as HCO+, OH, NH3. About one hundred of such sources are now recognized. They are often found in the vicinity of H2O masers, T Tauri stars, and Herbig-Haro objects. The central object is often observed as an infra-red source.
Protostars and Molecular Clouds
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