17μm molecular hydrogen line emission from OMC-1

The v=0-0 S(1) line of molecular hydrogen at 17.03μm has been measured in the source OMC-1 along a 90′′ cut passing through the near-IRH2 emission Peaks 1 and 2 using the Kuiper Airborne Observatory. The line flux is typically 50% of the 2.12μm v=1-0 S(1) line, but its distribution is somewhat more extended and it is relatively brighter at Peak 2.We interpret this as shocked emission coming from two regions of roughly equal brightness and lying close to the plane of the sky, plus a more extended contribution from slower shocks (∼ 5 km s−1) which do not contribute significantly to the near-IR vibrationalrotational lines. The 17μm line flux is an order ofmagnitude too strong to be explained by planar Jand C-shock models. However our data cannot distinguish between the merits of a cooling flow dominated by H2 line emission and the integrated emission from a C-type bow-shock. Both models predict column density ratios close to those observed from a variety of lines covering a range from 1 000 to 25 000K in upper state energy. We predict a flux for the ground state 28.2μm 0-0 S(0) line of ∼ 2% that of the 1-0 S(1) line at Peak 1, and suggest that a consistent set of observations of the lowest pure rotational lines of H2 would allow us to distinguish between these shock models.