Observations of Outflows from Young Stars

Recent near-IR observations of Herbig-Haro (HH) jets and molecular outflows from very young, deeply embedded protostars are discussed. Proper motion measurements, and both lowand high-resolution spectroscopic studies reveal the excitation and kinematics of individual objects, which may be interpreted in terms of highvelocity bow shocks which sweep up and entrain ambient material to form molecular “CO” outflows. The observed properties of many objects can be explained reasonably well with magnetized bow C-shock models, although J-type shocks cannot be ruled out. We also discuss new echelle observations of the outflow sources themselves. These H2 data reveal intermediate and high-velocity line emission from the base of the outflow (from within a few hundred AU of the driving source) in most of the flows observed. The properties of these “Molecular Hydrogen Emission Line”—or MHEL—regions, are similar to those of Forbidden Emission Line (FEL) regions towards T Tauri stars.