Herbig-Haro Objects (HHOs) are shock-excited nebulosities observed in star forming regions. They are powered by the energy released in the shocks between outflows from pre-main-sequence stars and interstellar gas (or previous ejecta). They were discovered in the Orion region by George Herbig and Guillermo Haro in the late forties. Ambartsumian (1954, 1957) called these nebulosities Herbig-Haro objects and suggested, for the first time, that they may be related with star formation. A recent review on these 50 years of HH objects research can be found in Reipurth & Heathcote (1997).
The IUE was well suited to study HH objects because shock waves emit strong lines (resonance and semiforbidden) in the UV range. However the detection of HH 1 with the IUE (Ortolani & D’Odorico, 1980) was somewhat surprising since HHOs were expected to be heavely extincted and moreover, the shock wave models available at the beginning of the IUE mission (Dopita 1978, Schwartz 1978, Raymond 1979) predicted lower line fluxes than what, at the end, was observed with the IUE.
During the IUE lifetime (1978-1996) up to 19 HHOs were observed (see Sect. 4) but only 11 were actually detected, in fact, rather sofisticated extraction (and observation) techniques were used to detect 3 of them namely, HH 7, HH 11 and HH 29 (Cameron & Liseau, 1990, Liseau et al 1996). The following is just a brief summary on the UV spectral characteristics of the HH objects (as measured with the IUE) and on the main contributions of the IUE to this research field.
Background information is presented on the Herbig-Haro nebulosities observed with the IUE until the end of the mission. The log of observations and the UV spectrum are provided for all the objects. This information is completed with basic data on the individual sources.