Molecular Hydrogen Emission from Herbig-Haro Objects

Abstract The faint emission line knots known as Herbig–Haro objects (Herbig 1951; Haro 1952) have been shown to be shock waves driven by (and in) outflows from young stars (Schwartz 1977; Dopita 1978; Raymond 1979). They are typically 0.1 pc long, with densities of order .104 cm-3. Doppler shifts and proper motions of 100–400 km s-1 arecommon, and the exciting stars are most often classical T Tauri stars.