Abstract We present a comprehensive study on the physical and chemical structures of a chemically rich bipolar outflow in a high-mass star-forming region IRAS 16272−4837 (SDC335), utilizing high-resolution spectral line data at 1.3 and 3 mm dual bands from the Atacama Large Millimeter/submillimeter Array, ATOMS, and QUARKS surveys. The high-velocity jet is enveloped by a lower-velocity outflow cavity, containing bright knots that show enhanced molecular intensities and elevated excitation temperatures. Along the outflow, we have identified 35 transitions from 22 molecular species. By analyzing the spatial distribution and kinematics of these molecular lines, we find that the molecular inventory in the outflow is regulated by three processes: (i) direct entrainment from the natal molecular core by the outflow; (ii) shock-induced release of molecules or atoms from dust grains; and (iii) thermal desorption and gas-phase reactions driven by shock heating. These results confirm that outflows are not only dynamical structures but also active chemical factories, where entrainment, shocks, and thermal processing jointly enrich the molecular content. Our findings confirmed that outflow chemistry has a multiorigin nature, and provide critical insights into chemical evolution during high-mass star formation.

Context. Recent studies indicate that the formation of planets in protoplanetary disks begins early in the embedded Class 0/I phases of protostellar evolution. The physical and chemical makeup of the embedded phase can provide valuable insights into the process of star and planet formation. Aims. This study aims to provide a thorough overview of the various morphologies for molecular emissions observed on disk scales (≲100 au) toward nearby embedded sources. Methods. We present high angular resolution (0 ⋅ ′′ 1, ~ 15 au) molecular line emissions for 12 CO, 13 CO, C 18 O, SO, SiO, DCN, CH 3 OH, H 2 CO, and c –C 3 H 2 toward 19 nearby protostellar sources in the context of the Atacama Large Millimeter/submillimeter Array (ALMA) Large Program “Early Planet Formation in Embedded Disks (eDisk).” Results. Emissions in 12 CO are seen toward all sources and primarily trace outflowing materials. A few sources also show high-velocity jets in SiO emission and high-velocity channel maps of 12 CO. The 13 CO and C 18 O emissions are well-known tracers of high-density regions and trace the inner envelope and disk regions with clear signs of rotation seen at continuum scales. The large-scale emissions of 13 CO also delineate the outflow cavity walls where the outflowing and infalling materials interact with each other, and exposure to UV radiation leads to the formation of hydrocarbons such as c –C 3 H 2 . Both DCN and CH 3 OH, when detected, show compact emissions from the inner envelope and disk regions that peak at the position of the protostar. The CH 3 OH emissions are contained within the region of DCN emissions, which suggests that CH 3 OH traces the hot core regions. Likewise, a few sources, also display emissions in CH 3 OH toward the outflow. Both SO and H 2 CO show complex morphology among the sources, suggesting that they are formed through multiple processes in protostellar systems.

Abstract Magnetic fields influence the structure and evolution of protostellar systems; thus, understanding their role is essential for probing the earliest stages of star formation. We present Atacama Large Millimeter/submillimeter Array Band 3 and 6 polarized continuum observations at ∼0 . ″ 5 resolution toward the Class 0 protostellar system HH 211. Three dust filaments (∼4000 au in length) are found in the HH 211 protostellar envelope, two of which are aligned with core-scale (∼10,000 au) magnetic fields detected by previous James Clerk Maxwell Telescope observations. This result suggests that the formation of the dust filaments may be influenced by magnetic fields. In the inner envelope (∼1000 au), we detect a clear hourglass-shaped magnetic field morphology near the protostar and toroidal fields along the outflow directions. We also estimate the line-of-sight averaged temperature and column density distributions in the inner envelope and find that the temperature is higher in the east, while the column density is enhanced in the southern and western regions. The southern dense regions of the inner envelope may trace either outflow cavity walls, due to their alignment with the outflow, or possible infalling channels in the midplane, given the close correspondence between the observed magnetic fields and the predicted infall trajectories.

Abstract Optical and infrared surveys have detected increasing numbers of disc accretion outbursts in young stars. Some models of these FU Ori-type events predict that the outburst should start at near- to mid-infrared wavelengths before an optical rise is detected, and this lag between infrared and optical bursts has been observed in at least two systems. Detecting and characterizing infrared precursors can constrain the outburst trigger region, and thus help identify the mechanism producing the outburst. However, because FU Ori objects are generally young and usually embedded in dusty protostellar envelopes, it is not clear whether or how well such infrared precursors can be detected in the presence of strong envelope extinction. To explore this question, we combine time-dependent outburst models of the inner disc with an outer dusty disc and protostellar envelope, and calculate the resulting spectral energy distributions (SEDs) using the radiative transfer code RADMC3D. We find that, for envelope mass infall rates ≳ 10−5M⊙ yr−1 (rc/30 au)−1/2, where rc is a characteristic inner radius for the infalling envelope, the infrared precursor is only apparent in the SED when viewed along an outflow cavity. At other inclinations, the precursor is most easily distinguished with limited envelope extinction at infall rates ≲ 10−6M⊙ yr−1 (rc/30 au)−1/2. We also show that far-infrared and submm/mm monitoring can enable the indirect detection of precursor evolution long before the optical outburst, emphasizing the potential of long-wavelength monitoring for studying the earliest stages of protostar formation.

Abstract One possible explanation for the presence of very large grains (VLGs) larger than 10 μ m in the inner envelope of intermediate-mass Class 0/I young stellar objects is their migration from the protostellar disk via outflows. To assess whether RATD hinders this grain transport, we conducted numerical modeling of RATD alongside grain dynamics, using gas velocity and density profiles from an MHD simulation of an intermediate Class 0 protostar. Our results show that, when the central luminosity L center is ≥5 L ⊙ , porous grains larger than 1 μ m with tensile strengths S max ∼ 1 0 3 - 1 0 4 erg cm − 3 are efficiently destroyed by RATD at the outflow within ∼1 yr. This limits the outward migration of VLGs/submillimeter grains and leads submicron grains to dominate a few hundred astronomical unit inside the outflow cavity until L center drops below <5 L ⊙ . In contrast, L center > 20 L ⊙ is required for RATD significantly affecting aggregate/composite grains with higher S max ≥ 1 0 5 erg cm − 3 . We further incorporated RATD into POLARIS under the assumption that grains remain stationary. POLARIS accurately models the disruption for porous grains, but overestimates results for aggregate/composite grains at L center = 100 L ⊙ . At such high luminosities, the destruction of VLGs with S max ∼ 1 0 3 - 1 0 4 erg cm − 3 within the outflow cavity wall and inner envelope (after ∼20 yr) can reduce the observed polarization degree along the cavity wall by a factor of 2. However, RATD is not the dominant factor shaping dust polarization; magnetic inclusions, such as iron, play a more significant role.

Context. The (sub-)millimetre dust opacity spectral index (β) is a critical observable for constraining dust properties, such as the maximum grain size of an observed dust population. It has been widely measured at Galactic scales and down to protoplanetary disks. Because of observational and analytical challenges, however, quite a gap exists in following the evolution of dust in the interstellar medium (ISM): we lack measures of the dust properties in the envelopes that feed newborn protostars and their disks. Aims. To fill this gap, we used sensitive dust continuum emission data at 1.2 and 3.1 mm from the ALMA FAUST Large Program and constrained the spectral index of the submillimetre dust opacity for a sample of protostars. Methods. Our high-resolution data, along with a method that was more refined than the methods in previous efforts, allowed us to distinguish the contributions from the disk and envelope in the uv-plane, and thus, to measure spectral indices for the envelopes that are not contaminated by the optically thick emission of the inner disk regions. Results. The FAUST sources (n = 13) include a variety of morphologies in continuum emission: compact young disks, extended collapsing envelopes, and dusty outflow cavity walls. Firstly, we found that the young disks in our sample are small (down to < 9 au) and optically thick. Secondly, we measured the dust opacity spectral index β at envelope scales for n = 11 sources: The β of n = 9 of these sources were not constrained before. We effectively doubled the number of sources for which the dust opacity spectral index β has been measured at these scales. Thirdly, by combining the available literature measurements with our own (a total n = 18), we showed the distribution of the envelope spectral indices between ISM-like and disk-like values. This bridges the gap in the inferred dust evolution. Finally, we statistically confirmed a significant correlation between β and the mass of protostellar envelopes, as previously suggested in the literature. Conclusions. Our findings indicate that the optical dust properties smoothly vary from the ISM (≫ 0.1 parsec) through envelopes (∼ 500–2000 au) to protoplanetary disks (< 200 au). Multi-wavelength surveys including longer wavelengths and in controlled starforming regions are needed to further this study and make more general claims about the dust evolution in its pathway from the cloud to disks.

Context. Planet formation around young stars requires the growth of interstellar dust grains from micron-sized (μm-sized) particles to kilometre-sized (km-sized) planetesimals. Numerical simulations have shown that large (mm-sized) grains found in the inner envelope of young protostars could be lifted from the disc via winds. However, we are still lacking unambiguous evidence for large grains in protostellar winds and outflows. Aims. We investigated dust continuum emission in the envelope of the Class I binary L1551 IRS5 in the Taurus molecular cloud, aiming to identify observational signatures of grain growth, such as variations in the dust emissivity index (βmm). Methods. In this context, we present new, high-angular resolution (50 au) observations of thermal dust continuum emission at 1.3 mm and 3 mm in the envelope (∼3000 au) of L1551 IRS5, obtained as part of the ALMA-FAUST Large Program. Results. We analysed dust emission along the cavity walls of the CO outflow, extended up to ∼1800 au. We found an H2 volume density > 2 × 105 cm−3, a dust mass of ∼58 M⊕, and βmm ≲ 1, implying the presence of grains ∼103 times larger than typical sizes for the interstellar medium (ISM). Conclusions. We present the first spatially resolved observational evidence of large grains within an outflow cavity wall. Our results suggest that these grains have been transported from the inner disc to the envelope by protostellar winds and may subsequently fall back into the outer disc by gravity and/or via accretion streamers. This cycle provides longer time for grains to grow, demonstrating their crucial role in the formation of planetesimals.

Abstract The composition of protoplanetary disks, and hence the initial conditions of planet formation, may be strongly influenced by the infall and thermal processing of material during the protostellar phase. The composition of dust and ice in protostellar envelopes, shaped by energetic processes driven by the protostar, serves as the fundamental building material for planets and complex organic molecules. As part of the JWST General Observers program, “Investigating Protostellar Accretion,” we observed an intermediate-mass protostar HOPS 370 (OMC2-FIR3) using NIRSpec integral field unit and Mid-Infrared Instrument medium-resolution spectroscopy. This study presents the gas and ice phase chemical inventory revealed with the JWST in the spectral range of ∼2.9–28 μm and explores the spatial variation of volatile ice species in the protostellar envelope. We find evidence for the thermal processing of ice species throughout the inner envelope. We present the first high-spatial resolution (∼80 au) maps of key volatile ice species H2O, CO2, 13CO2, CO, and OCN−, which reveal a highly structured and inhomogeneous density distribution of the protostellar envelope, with a deficiency of ice column density that coincides with the jet/outflow shocked knots. Further, we observe high relative crystallinity of H2O ice around the shocked knot seen in the H2 and OH wind/outflow, which can be explained by a lack of outer colder material in the envelope along the line of sight due to the irregular structure of the envelope. These observations show clear evidence of thermal processing of the ices in the inner envelope, close to the outflow cavity walls, heated by the luminous protostar.

Abstract While molecular outflows have been studied in detail with radio interferometry, observations of the hotter gas in protostellar outflows at a comparable physical scale are often challenging. Combined with the Atacama Large Millimeter/submillimeter Array (ALMA), JWST allows us to investigate the cold and hot gas with unprecedented spatial resolution and sensitivity. We present a detailed comparison between the gas distributions probed with ALMA and JWST in the primary outflow of IRAS 15398−3359. At 2000 au scale, the southwestern outflow shows four shell structures in 5–10 μm continuum, whereas the submillimeter H2CO emission traces two of the four shells closest to the protostar. Submillimeter emission from CS, CCH, c–C3H2, and CH3OH shows the same two shells, and the 12CO emission covers most of the outflow region. SO and SiO only trace a condensation at the edge of the shell closest to the protostar. None of these lines observed with ALMA show the outermost shell. At 500 au scale, we find hot H2 gas inside the outflow cavity with JWST. The derived temperature of H2 is 1147 ± 198 K within a 0 . ″ 5 aperture at the protostar. The foreground mass column density of dust is (1.4–2.0) × 10−3 g · cm−2 (AV = 47–66 mag) in the outflow, using the dust model from J. C. Weingartner & B. T. Draine (2001). We also find an 8∘ difference between the directions toward the [Fe ii] knot and the outermost shell in the MIRI image, which may be interpreted as the precession of the [Fe ii] jet. The dynamical timescale of the [Fe ii] knot is 10 yr, suggesting a current event.

Abstract Utilizing the James Webb Space Telescope (JWST), the Atacama Large Millimeter/submillimeter Array (ALMA), and the Very Large Array (VLA), we present high angular resolution (0 . ″ 06–0 . ″ 42), multiwavelength (4 μm–3 cm) observations of the VLA 1623-2417 protostellar system to characterize the origin, morphology and, properties of the continuum emission. JWST observations at 4.4 μm reveal outflow cavities for VLA 1623 A and, for the first time, VLA 1623 B, as well as scattered light from the upper layers of the VLA 1623 W disk. We model the millimeter-centimeter spectral energy distributions to quantify the relative contributions of dust and ionized gas emission, calculate dust masses, and use spectral index maps to determine where optical depth hinders this analysis. In general, all objects appear to be optically thick down to ∼90 GHz, show evidence for significant amounts (tens to hundreds of M ⊕) of large (>1 mm) dust grains, and are dominated by ionized gas emission for frequencies ≲​​​​​​15 GHz. In addition, we find evidence of unsettled millimeter dust in the inclined disk of VLA 1623 B possibly attributed to instabilities within the circumstellar disk, adding to the growing catalog of unsettled Class 0/I disks. Our results represent some of the highest-resolution observations possible with current instrumentation, particularly in the case of the VLA. However, our interpretation is still limited at low frequencies (≲22 GHz) and thus motivates the need for next-generation interferometers operating at centimeter wavelengths.

Abstract The study of deuterium fractionation is a valuable tool for reconstructing our chemical history from the early prestellar stages to the formation of planets. In the context of the ALMA Large Programme FAUST, we observed formaldehyde, H2CO, and its singly and doubly deuterated forms, HDCO and D2CO, towards the protostellar cluster VLA1623–2417, on scales of ∼2000 − 50 au. Formaldehyde probes the inner envelopes of the protostars VLA1623A, B, and W, the rotating cavities opened by the VLA1623A outflow, and several streamers. The HDCO and D2CO emissions are observed towards VLA1623A, in its outflow cavities, and in one of the streamers. We estimate the gas temperature from the HDCO lines: T∼125 K towards VLA1623A, indicating hot-corino emission, lower temperatures in the outflow cavities (20 − 40 K), and in the streamers (≤15 K). The D2CO lines also trace the flattened envelope of VLA1623A, where H2CO and HDCO are fainter. This may be due to D2CO formation on dust grains in the cold prestellar phase, and subsequent photodesorption caused by the enhanced UV flux from two nearby B stars. We inferred the molecular deuteration: [HDCO]/[H2CO] ∼0.16, ∼0.07 − 0.13, and ∼0.3; [D2CO]/[H2CO] ∼0.003, ∼0.05 − 0.13, and ∼0.03 in the hot corino, in the outflow cavities, and in the streamer, respectively. The spatial distribution of D2CO, which points to formation on dust grains, and the similar values of [HDCO]/[H2CO] and [D2CO]/[H2CO] in the components of the system, suggest that deuterium fractionation occurs at the prestellar stage and is then inherited, mostly unaltered, in the protostellar phase.

ABSTRACT We confirmed the existence of a massive protocluster in G23.43−0.18 from our Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm continuum and molecular line observations. We resolved the region into one main massive protostellar object, G23.43−0.18 A, one intermediate mass protostellar object, G23.43−0.18 B, and three low mass objects, G23.43−0.18 C1, G23.43–0.18 C2, and G23.43−0.18 C3. A spiral arm structure is observed in G23.43−0.18 B. G23.43−0.18 A 1.3 mm dust continuum emission showed a ‘butterfly’ morphology with clear evidence of the existence of a cavity and bipolar outflow with an inclination angle of 50$^\circ$. G23.43−0.18 B presents a compact rotating structure, and possibly an inner Keplerian disc, traced with methanol lines and powers a jet revealed by multiple compact emission peaks in CO, indicating episodic ejections every 300 yr. The presence of 6.7 GHz methanol masers in G23.43−0.18 A and G23.43−0.18 B are strong indications that both objects host massive protostars and are good sites to test some theories of the early evolutionary phases of massive stars.

Studying outflows is important, as they may significantly contribute to angular momentum removal from a star-disc system and thus affect disc evolution and planet formation. To investigate the different outflow components, including the collimated jet, wide-angled molecular outflow, and outflow cavity, of the Class I HH 46/47 outflow system, we focused on their kinematics. We present near-infrared (NIR) K-band integral field observations of the blueshifted HH 46/47 outflow base obtained using VLT/SINFONI with an angular resolution of 0 Our analysis focuses on Fe ii H$_2$ 1–0 S(1), and Br-gamma emission. We employed a wavelength recalibration technique based on OH telluric lines in order to probe the kinematics of the wide-angled flow with an accuracy of sim 1 km s$^ $ - 3 km s$^ We confirmed a velocity gradient of sim 10 km s$^ $ transverse to the outflow direction in the wide-angled H$_2$ outflow cavity. We find that the H$_2$ cavity peaks at radial velocities of sim $-$15 km s$^ $ to $-$30 km s$^ $, and that the atomic jet peaks at $v_ rad $ sim $-$210 km s$^ $. The outflow exhibits a layered structure: The high-velocity Fe ii and Br-gamma jet is surrounded by a wide-angled H$_2$ outflow cavity that is in turn nested within the continuum emission and CO molecular outflow. The continuum emission and H$_2$ outflow cavity are asymmetric with respect to the jet axis. We propose that the origin of the asymmetries and the velocity gradient detected in the wide-angled H$_2$ cavity is due to a wide-angled outflow or successive jet bowshocks expanding into an inhomogeneous ambient medium or the presence of a secondary outflow. We eliminated outflow rotation as an exclusive origin of this velocity gradient due to large specific angular momenta values, $J(r)$ approx 3000 - 4000 km s$^ \,$au, calculated from 1 to 2 along the outflow and the fact that the sense of apparent rotation we detected is opposite to that of the CO envelope emission. The observations reveal the complexities inherent in outflow systems and the risk of attributing transverse velocity gradients solely to rotation.

We present James Webb Space Telescope (JWST) Mid-InfraRed Instrument (MIRI) observations of warm CO and H2O gas in emission toward the low-mass protostar IRAS 15398-3359, observed as part of the CORINOS program. The CO is detected via the rovibrational fundamental band and hot band near 5 μm, whereas the H2O is detected in the rovibrational bending mode at 6–8 μm. Rotational analysis indicates that the CO originates in a hot reservoir with an excitation temperature of 1598 ± 118 K, while the water is much cooler at 204 ± 7 K. Neither the CO nor the H2O line images are significantly spatially extended, constraining the emission to within ∼40 au of the protostar. The compactness and high temperature of the CO are consistent with an origin in the embedded protostellar disk, or in a compact disk wind. In contrast, the water must arise from a cooler region and requires a larger emitting area (compared to the CO) to produce the observed fluxes. The water may arise from a more extended part of the disk, or from the inner portion of the outflow cavity. Thus, the origin of the molecular emission observed with JWST remains ambiguous. Better constraints on the overall extinction, comparison with realistic disk models, and future kinematically resolved observations may all help to pinpoint the true emitting reservoirs.

The formation of the massive stars, and in particular, the role that the magnetic fields play in their early evolutionary phase is still far from being completely understood. Here, we present the Atacama Large Millimeter/submillimeter Array 1.2 mm full polarized continuum and H13CO+(3−2), CS(5−4), and HN13C(3−2) line observations with a high angular resolution (∼0.″4 or 1100 au). In the 1.2 mm continuum emission, we reveal a dusty envelope surrounding the massive protostars, IRAS16547-E and IRAS16547-W, with dimensions of ∼10,000 au. This envelope has a biconical structure likely carved by the powerful thermal radio jet present in region. The magnetic field vectors follow very well the biconical envelope. The polarization fraction is ∼2.0% in this region. Some of these vectors seem to converge to IRAS 16547-E and IRAS 16547-W, the most massive protostars. Moreover, the velocity fields revealed from the spectral lines H13CO+(3−2) and HN13C(3−2) show velocity gradients with a good correspondence with the magnetic fields, which maybe are tracing the cavities of molecular outflows or maybe infalling in some parts. We derived a magnetic field strength in some filamentary regions that goes from 2 to 6.1 mG. We also find that the CS(5−4) molecular line emission reveals multiple outflow cavities or bow shocks with different orientations, some of which seem to follow the NW–SE radio thermal jet.

ABSTRACT Molecular deuteration is a powerful diagnostic tool for probing the physical conditions and chemical processes in astrophysical environments. In this work, we focus on formaldehyde deuteration in the protobinary system NGC 1333 IRAS 4A, located in the Perseus molecular cloud. Using high-resolution ($\sim$100 au) ALMA (The Atacama Large Millimeter/submillimeter Array) observations, we investigate the [D$_2$CO]/[HDCO] ratio along the cavity walls of the outflows emanating from IRAS 4A1. Our analysis reveals a consistent decrease in the deuteration ratio (from $\sim$60-20 per cent to $\sim$10 per cent) with increasing distance from the protostar (from $\sim$2000 to $\sim$4000 au). Given the large measured [D$_2$CO]/[HDCO], both HDCO and D$_2$CO are likely injected by the shocks along the cavity walls into the gas-phase from the dust mantles, formed in the previous prestellar phase. We propose that the observed [D$_2$CO]/[HDCO] decrease is due to the density profile of the prestellar core from which NGC 1333 IRAS 4A was born. When considering the chemical processes at the base of formaldehyde deuteration, the IRAS 4A’s prestellar precursor had a predominantly flat density profile within 3000 au and a decrease of density beyond this radius.

We present ALMA Band 7 molecular line observations of the protostars within the VLA 1623 system. We detect C17O (3–2) in the circumbinary disk around VLA 1623A and the outflow cavity walls of the collimated outflow. We further detect redshifted and blueshifted velocity gradients in the circumstellar disks around VLA 1623B and VLA 1623W that are consistent with Keplerian rotation. We used the radiative transfer modelling code pdspy and simple flared disk models to measure stellar masses of 0.27 ± 0.03 M⊙, 1.9−0.2+0.3 M⊙, and 0.64 ± 0.06 M⊙ for the VLA 1623A binary, VLA 1623B, and VLA 1623W, respectively. These results represent the strongest constraints yet on stellar mass for both VLA 1623B and VLA 1623W, and the first mass measurement for all stellar components using the same tracer and methodology. We use these masses to discuss the relationship between the young stellar objects (YSOs) in the VLA 1623 system. We find that VLA 1623W is unlikely to be an ejected YSO, as has been previously proposed. While we cannot rule out that VLA 1623W is a unrelated YSO, we propose that it is a true companion star to the VLA 1623A/B system and that these stars formed in situ through turbulent fragmentation and have had only some dynamical interactions since their inception.

Magnetic fields likely play an important role in the formation of young protostars. Multiscale and multiwavelength dust polarization observations can reveal the inferred magnetic field from scales of the cloud to core to protostar. We present continuum polarization observations of the young protostellar triple system IRAS 16293-2422 at 89 μm using HAWC+ on SOFIA. The inferred magnetic field is very uniform with an average field angle of 89° ± 23° (E of N), which is different from the ∼170° field morphology seen at 850 μm at larger scales (≳2000 au) with JCMT POL-2 and at 1.3 mm on smaller scales (≲300 au) with Atacama Large Millimeter/submillimeter Array. The HAWC+ magnetic field direction is aligned with the known E-W outflow. This alignment difference suggests that the shorter wavelength HAWC+ data is tracing the magnetic field associated with warmer dust likely from the outflow cavity, whereas the longer wavelength data are tracing the bulk magnetic field from cooler dust. Also, we show in this source the dust emission peak is strongly affected by the observing wavelength. The dust continuum peaks closer to source B (northern source) at shorter wavelengths and progressively moves toward the southern A source with increasing wavelength (from 22 to 850 μm).

Massive protostars launch accretion-powered, magnetically collimated outflows, which play crucial roles in the dynamics and diagnostics of the star formation process. Here we calculate the shock heating and resulting free–free radio emission in numerical models of outflows of massive star formation within the framework of the Turbulent Core Accretion model. We postprocess 3D magnetohydrodynamic simulation snapshots of a protostellar disk wind interacting with an infalling core envelope, and calculate shock temperatures, ionization fractions, and radio free–free emission. We find heating up to ∼107 K and near-complete ionization in shocks at the interface between the outflow cavity and infalling envelope. However, line-of-sight averaged ionization fractions peak around ∼10%, in agreement with values reported from observations of massive protostar G35.20-0.74N. By calculating radio-continuum fluxes and spectra, we compare our models with observed samples of massive protostars. We find our fiducial models produce radio luminosities similar to those seen from low- and intermediate-mass protostars that are thought to be powered by shock ionization. Comparing to more massive protostars, we find our model radio luminosities are ∼10–100 times less luminous. We discuss how this apparent discrepancy either reflects aspects of our modeling related to the treatment of cooling of the post-shock gas or a dominant contribution in the observed systems from photoionization. Finally, our models exhibit 10 yr radio flux variability of ∼5%, especially in the inner 1000 au region, comparable to observed levels in some hypercompact H ii regions.

ABSTRACT The exploration of outflows in protobinary systems presents a challenging yet crucial endeavour, offering valuable insights into the dynamic interplay between protostars and their evolution. In this study, we examine the morphology and dynamics of jets and outflows within the IRAS 4A protobinary system. This analysis is based on ALMA observations of SiO(5–4), H2CO(30, 3–20, 3), and HDCO(41, 4–31, 3) with a spatial resolution of ∼150 au. Leveraging an astrochemical approach involving the use of diverse tracers beyond traditional ones has enabled the identification of novel features and a comprehensive understanding of the broader outflow dynamics. Our analysis reveals the presence of two jets in the redshifted emission, emanating from IRAS 4A1 and IRAS 4A2, respectively. Furthermore, we identify four distinct outflows in the region for the first time, with each protostar, 4A1 and 4A2, contributing to two of them. We characterize the morphology and orientation of each outflow, challenging previous suggestions of bends in their trajectories. The outflow cavities of IRAS 4A1 exhibit extensions of 10 and 13 arcsec with position angles (PA) of 0° and -12°, respectively, while those of IRAS 4A2 are more extended, spanning 18 and 25 arcsec with PAs of 29° and 26°. We propose that the misalignment of the cavities is due to a jet precession in each protostar, a notion supported by the observation that the more extended cavities of the same source exhibit lower velocities, indicating they may stem from older ejection events.