PROMPT ENTRAINMENT IN THE VARIABLE MOLECULAR JET FROM RNO 15-FIR

Optical, near-infrared, and sub-millimetre observations of the outflow from the young (Class I/Class 0) source RNO 15-FIR indicate that it i s jet-driven, and that the ''prompt'' or bow shock entrainment mechani sm dominates over ''turbulent'' entrainment. The CO J=3-2 observations presented in this paper reveal a collimated, bipolar, molecular outfl ow driven by RNO 15-FIR. The peaks in the CO outflow lobes are coincid ent with compact H-2 line emission features. We also find that the mas s and momentum distributions in both flow lobes decrease with distance from the source, and that localised ''peaks'' in these distributions coincide with the H-2 knots. It is likely, therefore, that the H-2 kno ts represent bow shocks along the jet which accelerate ambient gas int o the flow via a prompt entrainment mechanism. Careful analysis of the data also suggests that the molecular outflow is ''wiggling'' This va riation in flow direction is possibly due to the orbital motion of the outflow source about some unseen binary companion. The orbital period and binary separation estimated from a sinusoidal fit to the wiggling along the flow suggest two embedded sources with a combined mass of r oughly 12M..