ON THE NATURE OF THE EXCITATION OF HERBIG-HARO OBJECT-2

We present VLA observations of the NH3(1, 1) and NH3(2, 2) lines toward the HH 2 object using the D configuration. We detected several small (approximately 20') clumps located near HH 2. These clumps are cold, T(R)(2, 2; 1, 1) less-than-or-equal-to 20 K, and with narrow line widths, DELTA-V less-than-or-equal-to 1 km s-1. We find that these clumps appear a few arcseconds downwind with respect to the HH 2 optical knots and the H-2 [S(1), nu = 1 --> 0] line emission. The low temperatures and narrow line widths found in the ammonia clumps imply that they cannot be ambient clumps compressed as a whole by a shock wave. We suggest that these clumps are random ambient high-density clumps in the way of the collimated wind from VLA 1. Alternatively, they could be random ambient clumps with the observed ammonia emission enhanced by the radiation field generated at the bow shock of the jet, as proposed to explain the HCO+ emission near HH 1 and HH 2. However, detailed theoretical calculations will be needed to investigate this possibility. We favor an interstellar jet origin for HH 2. We suggest that the observed optical knots in HH 2 could be part of the bow shock of the VLA 1 jet, but now being disrupted and fragmented by the interaction with ambient clumps such as those observed in ammonia.