Ammonia emission downstream of the Herbig-Haro Object 1

We report VLA D-configuration NH3(1, 1) and (2, 2) observations of Herbig-Haro Object 1 (HH 1). In direct analogy to the case of HH 2 (Torrelles et al. 1992b), we have found ammonia emission immediately adjacent to and downstream of HH 1. As in the case of HH 2, there is no evidence of any significant perturbation in terms of heating and broadening of the ammonia lines. This high degree of symmetry between the HH 1 and HH 2 ammonia clumps implies a causal physical relationship between the HH objects and the ammonia emission, discarding the possibility that these clumps are just ambient clumps projected by chance downstream of the HH objects. In particular, we think that there is the possibility that these clumps delineate nearby ambient gas whose ammonia emission is enhanced by some still unknown process related to the radiation field generated at the head of the jet of the VLA-1 source. However, detailed theoretical calculations will be needed to investigate this possibility. We also detected two other clumps located to the southwest of HH 1. One of them, seen only in the (2, 2) line, coincides with an H2O maser, and its temperature (≳30 K) suggests that there might be a young star embedded in this clump. The other clump is located ∼15″ south of the H2O maser. We also detected ammonia emission from the previously reported condensation associated with VLA-1 (Rodríguez et al. 1990a). As it was also previously reported, this condensation consists of two halves with a velocity shift of ∼2 km s-1 of the same direction and sign as those of the HH 1-2 optical outflow. However, on dynamical considerations, we argue that this shift could represent expanding or contracting motions of a flattened structure seen almost edge-on, rather than a molecular outflow of low collimation.