A twin-jet structure rather than jet-rotation in the young stellar object OMC 2/FIR 6b

TL;DR

This study reinterprets ALMA observations of the young stellar object FIR6b's jet, suggesting a twin-jet structure rather than jet rotation, which simplifies jet-launching conditions and implies a binary companion may influence jet asymmetry.

Contribution

The paper provides evidence that the northeast jet of FIR6b is a twin-jet structure, challenging previous jet rotation hypotheses and proposing a binary companion as the cause of jet asymmetries.

Findings

ALMA data favors twin-jet interpretation over jet rotation

Jets have velocities much higher than escape speed from launch radii

Opposing jet asymmetries may result from a binary companion

Abstract

We analyse recent high-quality Atacama Large Millimeter Array (ALMA) molecular line mapping observations of the northeast jet of the young stellar object (YSO) OMC 2/FIR6b (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 Fir6b in terms of jet rotation leads to jet-launching radii of ~2-3AU. However, the velocities of the jets ~100-400 km/s are much larger than the escape speed from these radii. We argue that the northeast jet of FIR6b 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 FIR6b 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 sub-stellar binary companion on an eccentric orbit that is inclined to the accretion disk plane.