H2 Fluorescence in HH 7 and DR 21

We present evidence for Ly pumping of the Lyman band system of molecular hydrogen in Herbig-Haro 7 and the bipolar outflow DR 21. For this study we have measured several vibrational-rotational emission lines of H whose energy levels are widely spaced and ranging from 6000 ( = 1) to 25000 Kelvin ( = 4). We show that the near-infrared H emission from the shocked gas in HH 7 can be well described by a bow C-type shock. The enhanced emission observed from the higher energy levels ( > 3) can be well modelled by employing the Ly pumping mechanism.In the DR 21 outflow the multi-line study showed that different physical conditions exist in the eastern and western emission lobes. The higher H line ratios measured in the eastern lobe suggests a higher Ly pump rate which may be locally produced in the fast bowshocks. The FUV radiation field emanating from the central HII regions may in addition be exciting the Lyman and Werner bands of H in the molecular lobes.We show that the observed H emission can be interpreted in terms of a simple model consisting of a C-type bowshock, which produces the low excitation H emission, and a FUV radiation field with enough Ly line radiation to produce the high excitation H emission through fluorescence.