Molecular hydrogen observations of Cepheus A West ?

The Herbig–Haro complex GGD37 is an active region in the west of Cepheus A. We have used the ISO Short Wavelength Spectrometer (SWS) to investigate the physics of this region by observations of molecular hydrogen and forbidden atomic and ionic emission lines over a wide wavelength and excitation energy range. We find excitation temperatures of the emitting molecular gas to be between 700 and 11000 K, the former being thermal in nature, whilst the latter implies a contribution from non–thermal processes. Gas densities in the emitting region are at least 105 cm 3. An H2 ortho–to–para ratio of 3, equal to the ratio of statistical weights, is consistent with our observations. The forbidden transitions can be modelled by a planar J–shock with pre–shock density of 103 to 104 cm 3 and velocity 70 to 80 km s 1. The H2 lines cannot be fit by either a single planar J– or C–shock, but instead require a combination of at least two C–shocks with different pre–shock density, shock velocity and covering factor.