SUCCESSIVE EJECTION EVENTS IN THE L1551 MOLECULAR OUTFLOW

We report CO J = 2 --> 1 strip maps along the axis and across the lobe s of the L1551 molecular outflow. The overall structure of the outflow is more complicated than previously believed. In particular, we find at least four successive high-velocity features along the axis of the blueshifted lobe which are very suggestive of different ejection episo des. The well-known ''shell structure'' is restricted to the feature c losest to the exciting source, indicating that a simple hollow shell m odel is inappropriate to explain the overall outflow structure. In con trast, our data are more consistent with recent jet-driven models for bipolar outflows. The presence of different high-velocity features sug gest that the entraining jet could be of intermittent nature. We have also carried out high-sensitivity observations of (CO)-C-13 toward sel ected positions in the outflow, and we infer from them that self-absor ption effects in the CO wing profiles are unimportant.