Prompt entrainment in the variable molecular jet from RNO15-FIR

Optical, near-infrared, and sub-millimetre observations of the outflow from the young (Class I/Class 0) source RNO15-FIR indicate that it is jet-driven, and that the “prompt” or bow shock entrainment mechanism dominates over “turbulent” entrainment. The CO J=3-2 observations presented in this paper reveal a collimated, bipolar, molecular outflow driven by RNO15-FIR. The peaks in the CO outflow lobes are coincident with compact H2 line emission features. We also find that the mass and momentum distributions in both flow lobes decrease with distance from the source, and that localised “peaks” in these distributions coincide with the H2 knots. It is likely, therefore, that the H2 knots represent bow shocks along the jet which accelerate ambient gas into the flow via a prompt entrainment mechanism. Careful analysis of the data also suggests that the molecular outflow is “wiggling”. This variation 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 roughly 12M .