AMMONIA EMISSION FROM BOW SHOCKS IN THE L1157 OUTFLOW

We present high-resolution (approximate to 5 '') NH3(1, 1) and NH3(3, 3) observations toward the blue lobe of the remarkable bipolar outflow L1157. We find that the ammonia emission arises from several compact condensations that are well aligned with IRAS 20386+6751, the origin o f the outflow. The gas that emits in ammonia has been strongly affecte d by the outflow. In addition of having been accelerated, the gas has been heated to temperatures of more than 60-80 K (a factor of 5 with r espect to its quiescent value), and its ammonia abundance has been enh anced by more than an order of magnitude. We interpret the ammonia emi ssion as arising from a series of bow shocks along the outflow axis, a nd although we cannot detect the shocking agent, our observations sugg est that it is in the form of a highly collimated jet. The multiplicit y of the ammonia peaks along the outflow suggests the jet is episodic, and the emitting source is so reddened, that most likely represents a case of a Class 0 object.