Abstract
The observations of masers and compact HII regions near Herbig-Haro objects are reviewed. H2O masers and H-H objects are probably both manifestations of shocked gas in the outflowing envelopes of newly formed stars. H20 masers have been detected near HH 1, HH 7-11 and HH 19-24 and near GGD 4, 5-6, 12-15, 16-17, 25, 27-28, 29, 32-35 and 37. Most of these masers have luminosities ∼10^-7, which is smaller than the luminosities of masers near massive OB stars. VLB observations show that the components in HH 7-11/H20(A) are very small, ∼ 2x10^12 cm in diameter and clustered within an area of diameter 3x10^13 cm. The dispersal time for the maser is 1 year. Hence, the masing cloud could not have travelled intact from a distant source, but is probably excited locally at the interface between the stellar wind and ambient cloud. It should be possible to measure proper motions of the HH/H20 masers with either the VLA or VLB Network. Compact HIl regions have been observed with the VLA at 5 GHz near HH 7-11, and GGD 5-6, 12-15, 25, 27-28, 29, and 37. If they are optically thin at 5 GHz they correspond to B0-B3 stars, whereas if they are stellar wind sources they would be substantially more luminous. The conpact HIl regions near HH 7-11, GGD 12-15, and GGD 37 could be ionized by embedded stars that are the energy sources for the associated bipolar molecular outflows. However, the momentum rates in the flows exceed those inferred for the radiation fields.
