The Outflow of the B335 Protostar II: After the Outburst

TL;DR

This study leverages two-epoch JWST NIRCam imaging and NIRSpec IFU spectroscopy, plus background-star photometry and archival ALMA/VLA data, to dissect the impact of a major protostellar outburst in B335 on its outflow and surrounding envelope. By mapping continuum extinction and H$_2$O ice across the blue-shifted outflow cavity, the authors demonstrate a carved-out cavity with substantially lower dust and ice content, consistent with elevated temperatures and ice destruction in the outflow. They measure proper motions of multiple shock fronts, with the bright inner shock 3E tracing a fast, newly launched jet that interacts with older, slower material, while other shocks show diminishing CO excitation down the jet. The results reveal a coherent picture of episodic accretion driving a fast, CO-rich jet within a broader, CO-poor cavity, accompanied by shadowing and variability in the reflection nebula on yearly timescales. Collectively, the findings illuminate how accretion outburst activity shapes jet physics, cavity structure, and ice/dust processing in a deeply embedded protostar.

Abstract

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.

Figures (28)

• Figure 1: RGB color composite sky-subtracted image of the B335 outflow: F277W, F150W, F090W. This image clearly shows the "core shine" scattered light from the interstellar radiation field outlining the B335 cloud and core. The densest parts of the core, where the protostar is located, are seen as a depression in the scattered interstellar light, showing in a brownish color. In the center of this dark region, in the F277W filter images displayed in red, the bipolar reflection nebula, illuminated by the protostar appears in reddish color. A few contours (white lines) of the flux in the F444W filter are included to show the knots in the inner jet and the outline of the inner outflow cavity. The distant parts of the outflow cavity appear as a region of reduced scattered light in the eastern part of the image. The B335 cloud only contains one flattened dense molecular core. The extent of the stripe used for extracting the crosscuts shown in Figure \ref{['cloudshine-crosscuts']} is indicated by dashed lines. We have added labels (in red) for the distant shock fronts (appearing pink in this RGB image) in the eastern lobe, since this figure is the only one in this paper showing these shock fronts.
• Figure 2: Crosscuts in declination direction centered on the protostellar source (offset 0), between the dashed lines in Figure \ref{['cloudshine-image']}. The crosscuts are colored in wavelength order and the filters used are indicated. At the shortest wavelength (F150W, blue), B335 appears as a dark cloud against the background, the apparent size of which gets smaller with increasing wavelength (F200W, green). At even longer wavelengths, the reflection nebula illuminated by the protostar begins to be detectable (F277W, yellow), and becomes dominant in the F356W filter (red)
• Figure 3: Top: Cutout of the F356W image with smoothed ($\sigma$ = 15 pixels) contours of the continuum extinction overlaid, to demonstrate the relation between the outflow cavity and the cloud structure. The outflow cavity is traced by the bipolar reflection nebula. Bottom: The continuum extinction map in its original resolution shown in greyscale with smoothed contours of that map overlaid.
• Figure 4: top: Cutout of the image in F356W with smoothed ($\sigma$ = 15 pixels) contours of the H$_2$O ice column density overlaid. The outflow cavity is traced by the bipolar reflection nebula. Bottom: The H$_2$O ice column density map in its original resolution shown in greyscale with smoothed contours of that map overlaid.
• Figure 5: NEOWISE W1 and W2 light curve in Vega magnitudes. The epoch of the NIRSpec IFU (MJD 59838.0, 2022 Sept. 16, black line) and the two epochs of NIRCam imaging 2023 04 25 UTC (MJD 60059.1, 2023 Apr. 25, brown line, and MJD 60424.3, 2024 Apr. 24, green line) are indicated by vertical lines. We have also included the photometry based on Spitzer images in 2004 and 2016. The open red square is the large-aperture magnitude from Kim.2024.ApJ.961.108.COoutflow, the open circles are our raw and corrected r=4 magnitudes. We have indicated the ejection times of shocks 4Ea and 3E. Shock 3E was ejected in the early phase of the presently on-going outburst. The wind causing shock 4Ea was plausibly ejected during the earlier outburst indicated by the 2004 Spitzer photometry.