A spectacular molecular outflow in the Monoceros OB1 molecular cloud

We present detailed observations of CO, CS, infrared continuum, and H₂ emission from a large, highly collimated, bipolar outflow in the Monoceros OB1 molecular cloud. From the high-resolution observations of CO emission, we find evidence that molecular gas in the outflow is contained in a shell with higher velocity material situated interior to lower velocity material. We also find the observed velocities of outflow emission to increase with increasing distance from the center of the outflow, and the gas in the outflow to be clumpy. A peak in the distribution of CS emission from the ambient cloud has also been found between the two outflow lobes and may indicate the existence of a dense core of gas in which the driving source of the outflow has formed. In addition, we have detected shock-excited molecular hydrogen emission from the blueshifted lobe of the outflow. Six 2 μm sources have been detected in the direction of the outflow. Of these, two are the most likely candidate driving sources. One source is situated coincident on the sky with the peak of the CS emission, and the other has a spectral energy distribution which is steeply rising toward the far-infrared. However, analysis of the near-infrared and IRAS observations suggests that any driving source for the outflow must have a bolometric luminosity less than about 4.5 L_⊙. The ratio of driving source radiant luminosity to flow mechanical luminosity is less than or equal to 1.8, an order of magnitude lower than that determined for any other known outflow source. This suggests that it is unlikely for this flow to be driven by stellar radiation from a central source since conversion efficiences in excess of 50% from stellar luminosity to flow mechanical luminosity would be required.