Jet Motion, Internal Working Surfaces, and Nested Shells in the Protostellar System HH 212

TL;DR

This study provides high-resolution observations of the HH 212 protostellar jet, revealing detailed structures, kinematics, and potential instabilities, advancing understanding of jet dynamics in early star formation.

Contribution

First detailed SiO and CO mapping of HH 212's inner jet at high resolution, revealing internal working surfaces, nested shells, and jet wiggles, with implications for jet stability and evolution.

Findings

Jet consists of knots, bow shocks, and sinuous structures.

Nested shells driven by knots and bow shocks are observed.

Jet exhibits a semi-periodical wiggle with a ~93-year period.

Abstract

HH 212 is a nearby (400 pc) highly collimated protostellar jet powered by a Class 0 source in Orion. We have mapped the inner 80" (~ 0.16 pc) of the jet in SiO (J=8-7) and CO (J=3-2) simultaneously at ~ 0.5 resolution with the Atacama Millimeter/Submillimeter Array at unprecedented sensitivity. The jet consists of a chain of knots, bow shocks, and sinuous structures in between. As compared to that seen in our previous observations with the Submillimeter Array, it appears to be more continuous, especially in the northern part. Some of the knots are now seen associated with small bow shocks, with their bow wings curving back to the jet axis, as seen in pulsed jet simulations. Two of them are reasonably resolved, showing kinematics consistent with sideways ejection, possibly tracing the internal working surfaces formed by a temporal variation in the jet velocity. In addition, nested shells are seen in CO around the jet axis connecting to the knots and bow shocks, driven by them. The proper motion of the jet is estimated to be ~ 115+-50 km/s, comparing to our previous observations. The jet has a small semi-periodical wiggle, with a period of ~ 93 yrs. The amplitude of the wiggle first increases with the distance from the central source and then stays roughly constant. One possible origin of the wiggle could be the kink instability in a magnetized jet.