The bipolar outflow toward G5.89-0.39

We present high-resolution observations of G5.89-0.39 in CO(1 → 0), ¹³CO(1 → 0), C¹⁸O(1 → 0), and HCO⁺(1 → 0). We characterize the G5.89-0.39 outflow using the ¹³CO emission. The outflow is found to be young, massive, and powerful. We conclude that (1) the outflow is nearly along the line of sight, (2) there is dynamical evidence for entrainment of ambient interstellar material into the outflow, (3) the mass entrainment rate is ∼4 × 10^-3 M_⊙ yr^-1, (4) in the blue lobe, only ∼27% of the outflow mass is due to entrainment, and (5) expansion of the outflow lobes perpendicular to the flow axis is occurring at ∼1-10 v_sound. A neutral and ionized outflow tracer are compared. Watson and coworkers predicted that if entrainment through the Kelvin-Helmholtz shear instability adds significantly to the outflow mass, a difference in the turbulent velocity widths of neutral and ionized outflow tracers could be measurable. We cannot conclude that the Kelvin-Helmholtz shear instability is the physical process causing this entrainment, but it may operate at a level below our detection limit.