The Outflow of the B335 Protostar II: After the Outburst

The B335 protostar has undergone a major outburst detected in the scattered light of its outflow cavity that has not yet ended. B335 therefore offers the rare opportunity to study its effect on the jet of a protostellar object. Photometry of background stars behind B335 is used to map visual continuum extinction and H$_2$O ice absorption and demonstrates that the outflow has carved out a cavity. Precise proper motions of the shock fronts emerging from the B335 protostar were obtained. The kinematic age of the most prominent shock front (3E) corresponds to the early phases of the ongoing outburst of the B335 protostar. Shock 3E shows strong CO gas emission, as well as H$_2$ and [\ion{Fe}{2}] emission. Older shock fronts show diminished CO emission and are dominated by H$_2$ and [\ion{Fe}{2}]. The emission feature 0E, closest to the protostar, is distinct in proper motion and radial velocity from the other shock fronts in the jet. In the span of 4\arcsec\ closest to the protostar, the continuum extinction in front of the outflow cavity increases by A$_V$~$\approx$~200 mag. The CO-line-removed spectra close to the protostar show the unsaturated absorption features of $^{13}$CO$_2$, OCN$^-$, and OCS have strongly increasing column densities toward the protostar. The ice characteristics are overall similar to those found in lines of sight with less extinction. The central regions of the bipolar nebula show CO gas emission, but at distances of a few arcsec from the protostar, absorption by CO gas is also detected.

💡 Research Summary

The paper presents a comprehensive study of the B335 protostar, which is currently undergoing a major accretion outburst that was first detected through enhanced scattered light in its outflow cavity. Using two epochs of JWST NIRCam imaging (F444W) taken in 2023 and 2024, together with a JWST NIRSpec IFU data set from 2022 and complementary ALMA observations, the authors map visual extinction, water‑ice absorption, and gas‑phase CO across the region, and they measure the proper motions of individual shock fronts in the jet.

Background‑star photometry reveals that the outflow has carved a low‑density cavity, while the line‑of‑sight extinction rises dramatically to A_V ≈ 200 mag within 4″ of the protostar. Ice spectroscopy shows unsaturated absorption from ^13CO₂, OCN⁻, and OCS, whose column densities increase sharply toward the source, yet the overall ice composition remains similar to that seen in lower‑extinction lines of sight.

Proper‑motion analysis, performed by cross‑correlating the two NIRCam epochs after careful astrometric alignment (including a measured proper motion of the protostar itself from ALMA data), yields precise velocities for the shock knots labeled 0E, 0Wn, 0Ws, 1E‑8E. The most recent, brightest knot (3E) has a kinematic age of only a few decades, consistent with the early phase of the ongoing outburst. Knot 3E exhibits strong CO (2‑1) emission together with H₂ 1‑0 S(1) and