EVIDENCE FOR MULTIPLE OUTBURSTS FROM THE CEPHEUS-A MOLECULAR OUTFLOW

We report evidence for multiple episodes of outflow activity in the Ce pheus A star-forming region. We present new, high signal-to-noise CSO observations of (CO)-C-12 5 = 3 --> 2, (CO)-C-13 5 = 3 --> 2, and CS J = 7 --> 6 emission. We also present new, interferometric and single-d ish observations of (CO)-C-12 J = 1 --> 0 emission toward the Cepheus A molecular outflow. Using line core velocity centroid maps, we argue that the multiple self-absorption features in the CO J = 3 --> 2 line profiles are tracing cool shells of material swept-up by an episodic o utflow. We present the results of a flexible three-dimensional LTE out flow model and radiative transfer code that best explain the observati ons as tracing multiple generations of outflow. The difference in the dynamical timescales between the ''old'' and ''new'' swept-up shells g ives an estimate of similar to 1.6 x 10(5) yr between the two generati ons of outbursts. The high-resolution (CO)-C-12 J = 1--> 0 maps obtain ed by combining single-dish observations with interferometric data cle arly show a shell-like morphology at low velocities. This cool shell a ppears to encompass the hot, extremely high velocity (EHV) winds seen in the J = 3 --> 2 transition. The interferometric observations show t hat the current generation of outflow is being powered by the object C epheus A-HW 2. There is also evidence for redirection of the blueshift ed lobe of the current generation of outflow, possibly by the extended NH3 structure Cep A-3. We present a model of the outflow geometry tha t can explain most of the observed structures in Cepheus A. The rotati ng, dense core traced by the CS observations is similar to 0.32 pc in diameter and has an estimated dynamical mass of 330 M.. The velocity s tructure of the core suggests that it is being disrupted by the high-v elocity winds driving the molecular outflow. This new technique of ext racting information from self-absorbed line profiles could be used to study other deeply embedded protostellar systems. Since outflows are b elieved to be intimately tied to accretion, such studies could lead to constraints on mass accretion models for young stellar objects.