HOPS 361-C's Jet Decelerating and Precessing Through NGC 2071 IR

TL;DR

This study uses multi-epoch HST and SOFIA observations to analyze the deceleration and precession of the jet from protostar HOPS 361-C in NGC 2071 IR, revealing a decelerating, precessing jet with specific physical and geometric properties.

Contribution

It presents the first detailed model of a precessing, decelerating jet from a protostar, combining proper motion measurements, emission line ratios, and new infrared spectra to characterize jet dynamics and environment.

Findings

Jet knots decelerate from 350 to 100 km/s with distance.

Precession period estimated at 1,000–3,000 years.

Jet is embedded at 1/5 to 4/5 of cloud depth.

Abstract

We present a two-epoch Hubble Space Telescope (HST) study of NGC 2071 IR highlighting HOPS 361-C, a protostar producing an arced 0.2 parsec-scale jet. Proper motions for the brightest knots decrease from 350 to 100 km/s with increasing distance from the source. The [Fe II] and Pa$\beta$ emission line intensity ratio gives a velocity jump through each knot of 40--50 km/s. A new [O I] 63 \mic\ spectrum, taken with the German REciever for Astronomy at Terahertz frequencies (GREAT) instrument aboard Stratospheric Observatory for Infrared Astronomy (SOFIA), shows a low line-of-sight velocity indicative of high jet inclination. Proper motions and jump velocities then estimate 3D flow speed for knots. Subsequently, we model knot positions and speeds with a precessing jet that decelerates. Measurements are matched with a precession period of 1,000--3,000 years and half opening angle of $15^\circ$. The [Fe II] 1.26-to-1.64 \mic\ line intensity ratio determines visual extinction to each knot from 5--30 mag. Relative to $\sim$14 mag of extinction through the cloud from $\rm{C}^{18}$O emission maps, the jet is embedded at a 1/5 to 4/5 fractional cloud depth. Our model suggests the jet is dissipated over a 0.2 pc arc. This short distance may result from the jet sweeping through a wide angle, allowing the cloud time to fill cavities opened by the jet. Precessing jets contrast with nearly unidirectional protostellar jets that puncture host clouds and can propagate significantly further.