1999ApJ...522..921G

We present high angular resolution and multitransition HCO⁺ observations toward the NGC 2071 molecular outflow. Comparison of the high-velocity (HV) HCO⁺ and the near-IR H₂ in the molecular outflow shows a clear correlation. At high HCO⁺ flow velocities the spatial coincidence is especially remarkable. In addition, the HV HCO⁺ presents clear morphological and kinematical differences with the CO outflow. These differences appear not only in the HV HCO⁺ emission associated with the H₂ but in the overall outflow. There is a clear HCO⁺ emission enhancement, relative to CO, at increasing flow velocities. This enhancement is probably due to an abundance enhancement produced by a velocity-dependent chemistry in the shocks. An overabundance of CH in low Mach shocks may cause the HCO⁺ abundance enhancement. Because of the short cooling time for H₂, the correlation between the HCO⁺ and the H₂ implies that HCO⁺ emission can provide a useful tool to study in detail the current interactions of protostellar winds with the dense ambient medium. At the position of the extremely high velocity (EHV) CO component in the red lobe we detect HCO⁺ (J=3⟶2) emission within the velocity range of the EHV CO gas. This emission is roughly compatible with the expected HCO⁺ emission associated with EHV gas arising from behind dissociative shocks.