UV observations of Herbig-Haro objects associated with bipolar molecular outflows : HH 7, HH 11 and HH 29.

Abstract

Results are presented of IUE observations of three shock excited visible Herbig-Haro nebulae: HH7, HH 11, and HH 29. With the possible exception of HH 11, large deviations were found from the 2 2S-1 2S two-photon decay continuum of atomic hydrogen. It was also found that the continuum of HH 29 varies considerably in both the intensity and the spectral slope. A model accounting for the clumpiness of the interstellar medium at the position of HH 29 is proposed, that explains the continuum and line changes with time in this object. A UV color index for Herbig-Haro objects is proposed, which is extinction-free (if the dust surrounding and/or within the objects consists predominantly of large grains). By applying this color index to available observations for eight HH objects, it is shown that the results obtained with the IUE are not accurate enough for detailed comparisons between theory and observations.