Abstract
The Herbig-Haro objects are optical nebulosities excited by a shock wave produced by the wind of a young star. A review of recent radio observations of Herbig-Haro objects and their environment is presented. Studies of neutral gas (both molecular and atomic) can give us information on three key components of these regions of recent star formation and outflows: (1) the dense, quiescent (Δν ≅ 1 km s-1) gas surrounding the exciting source of the outflow, (2) the high-velocity (Δν ≅ 10 km s-1) bipolar outflow gas, most probably ambient gas accelerated by a stellar wind and, (3) the extremely-high-velocity (Δν ≅ 100 km s-1) gas that may be the stellar wind itself or at least be very closely associated with it. The ionized gas component can also be studied via its free-free emission, and radio observations of this continuum emission from the HH objects and their exciting sources is also developing into a powerful technique to study the outflow phenomenon in star-forming regions. Some examples of radio continuum emission from Herbig-Haro objects are discussed.
