A Twin-jet Structure Rather than Jet Rotation in the Young Stellar Object OMC 2/FIR 6b

Abstract

Abstract We analyze recent high-quality Atacama Large Millimeter Array (ALMA) molecular line mapping observations of the northeast jet of the young stellar object (YSO) OMC 2/FIR 6b (HOPS-60) and find that these ALMA observations are much more likely to indicate a twin-jet structure than jet rotation, as previously hypothesized. The interpretation of the line-of-sight velocity gradient across (perpendicular to its axis) the northeast jet of Fir 6b in terms of jet rotation leads to jet-launching radii of ≃2–3 au. However, the velocities of the jets ≃100–400 km s−1 are much larger than the escape speed from these radii. We argue that the northeast jet of FIR 6b is instead compatible with a twin-jet structure, as observed in some planetary nebulae. Specifically, we find that the main, redshifted jet emanating from the central YSO is composed of two, very closely aligned, narrower jets that were launched by the central YSO at about the same time but at different inclinations with respect to the plain of the sky. This twin-jet structure removes the extreme requirement that jets with velocities similar to the escape velocity from the YSO be launched from very large radii. The YSO FIR 6b and certain planetary nebulae also share the characteristics of unequal structures and intensities of their two opposing bipolar jets. We propose that such opposing lobe asymmetries can result from a substellar binary companion on an eccentric orbit that is inclined to the accretion disk plane.