Outflow Cavity Research Articles

Spiral Arm, Rotating Structure and Outflow Cavity in Massive Star-Forming Region G23.43−0.18

Abstract We confirmed the existence of a massive proto-cluster in G23.43−0.18 from our ALMA 1.3 mm continuum and molecular line observations. We resolved the region into 1 main massive protostellar object, G23.43−0.18 A, 1 intermediate mass protostellar object, G23.43−0.18 B, and 3 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○. G23.43−0.18 B presents a compact rotating structure, and possibly an inner Keplerian disk, traced with methanol lines and powers a jet revealed by multiple compact emission peaks in CO, indicating episodic ejections every 300 years. 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.

A kinematical study of the launching region of the blueshifted HH 46/47 outflow with SINFONI K-band observations

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.

CORINOS. II. JWST-MIRI Detection of Warm Molecular Gas from an Embedded, Disk-bearing Protostar

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.

Magnetic Fields in Massive Star-forming Regions (MagMaR). IV. Tracing the Magnetic Fields in the O-type Protostellar System IRAS 16547–4247

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.

FAUST XIX. D2CO in the outflow cavities of NGC 1333 IRAS 4A: Recovering the physical structure of its original prestellar core

FAUST XIX. D2CO in the outflow cavities of NGC 1333 IRAS 4A: Recovering the physical structure of its original prestellar core

Constraining the stellar masses and origin of the protostellar VLA 1623 system

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 Observed along the East–West Outflow of IRAS 16293-2422

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).

Disk Wind Feedback from High-mass Protostars. IV. Shock-ionized Jets

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.

Multiple chemical tracers finally unveil the intricate NGC 1333 IRAS 4A outflow system. FAUST XVI

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.

JWST/NIRCam Imaging of Young Stellar Objects. III. Detailed Imaging of the Nebular Environment around the HL Tau Disk

As part of the James Webb Space Telescope (JWST) Guaranteed Time Observation program “Direct Imaging of YSOs” (program ID 1179), we use JWST NIRCam’s direct imaging mode in F187N, F200W, F405N, and F410M to perform high-contrast observations of the circumstellar structures surrounding the protostar HL Tau. The data reveal the known stellar envelope, outflow cavity, and streamers, but do not detect any companion candidates. We detect scattered light from an inflowing spiral streamer previously detected in HCO+ by the Atacama Large Millimeter/submillimeter Array, and part of the structure connected to the c-shaped outflow cavity. For detection limits in planet mass we use BEX evolutionary tracks when M p < 2 M J and AMES-COND evolutionary tracks otherwise, assuming a planet age of 1 Myr (youngest available age). Inside the disk region, due to extended envelope emission, our point-source sensitivities are ∼5 mJy (37 M J) at 40 au in F187N and ∼0.37 mJy (5.2 M J) at 140 au in F405N. Outside the disk region, the deepest limits we can reach are ∼0.01 mJy (0.75 M J) at a projected separation ∼ 525 au.

The kinematic and dynamic properties of HBC 494’s wide-angle outflows

ABSTRACT We present Atacama Large Millimeter/sub-millimeter Array (ALMA) Cycle-5 observations of HBC 494, as well as calculations of the kinematic and dynamic variables which represent the object’s wide-angle bipolar outflows. HBC 494 is a binary FU Orionis type object located in the Orion A molecular cloud. We take advantage of combining the ALMA main array, Atacama Compact Array (ACA), and Total Power (TP) array in order to map HBC 494’s outflows and thus, estimate their kinematic parameters with higher accuracy in comparison to prior publications. We use 12CO, 13CO, C18O, and SO observations to describe the object’s outflows, envelope, and disc, as well as estimate the mass, momentum, and kinetic energy of the outflows. After correcting for optical opacity near systemic velocities, we estimate a mass of 3.0 × 10−2 M⊙ for the southern outflow and 2.8 × 10−2 M⊙ for northern outflow. We report the first detection of a secondary outflow cavity located approximately 15 arcsec north of the central binary system, which could be a remnant of a previous large-scale accretion outburst. Furthermore, we find CO spatial features in HBC 494’s outflows corresponding to position angles of ∼35° and ∼145°. This suggests that HBC 494’s outflows are most likely a composite of overlapping outflows from two different sources, i.e. HBC 494a and HBC 494b, the two objects in the binary system.

Seven-year periodic variations in the methanol maser line displayed by the massive protostar IRAS\,20216+4104

We report the discovery and analysis of a periodic methanol maser in the massive protostar IRAS\,20216+4104. To obtain the light curve, we used the 6.7\,GHz methanol maser spectra collected between 2000-2003 and 2009-2023 with the Hartebeesthoek and Torun radio telescopes, as well as spectra from the literature reported prior to 1992. The velocity-integrated flux density shows sinusoidal-like variations with a period of 6.9pm 0.03\,yr. All but one of the features show periodic changes with a relative amplitude of 2 up to $&gt;$89. A slightly variable feature displays a moderate anti-correlation between the flux density and the other significantly variable features. The maser emission appears to follow the continuum emission of the red-shifted outflow cavity. A maximum emission of 3.4 and 4.6\,mu m precedes the maser peak by 15&lt;!PCT!&gt; of the period and the (infrared) IR light centroids show time-dependent displacement. The periodic behaviour of the maser and IR emission is likely due to the eclipsing effect from a wobbling inner disk.

ALMA and VLBA views on the outflow associated with an O-type protostar in G26.50+0.28

Protostellar jets and outflows are essential ingredients of the star formation process. A better understanding of this phenomenon is important in its own right as well as for many fundamental aspects of star formation. Jets and outflows associated with O-type protostars are rarely studied with observations reaching the close vicinity of the protostars. In this work, we report high-resolution ALMA and VLBA observations to reveal a clear and consistent picture of an outflow associated with an O-type protostar candidate in the G26.50+0.28 region. These observations reveal, for the first time, a collimated jet located in the middle of the outflow cavity. The jet is found to be perpendicular to an elongated disk/toroid and its velocity gradient. The collimated jet appears to show a small amplitude (α≈0°.06) counterclockwise precession, when looking along the blueshifted jet axis from the strongest continuum source MM1, with a precession length of 0.22 pc. The inclination of the jet is likely to be very low (≈8°), which makes it a promising target to study its transverse morphologies and kinematics. However, no clear evidence of jet rotation is found in the ALMA and VLBA observations. The three-dimensional velocities of the water maser spots appear to show the same absolute speed with respect to different opening angles, suggesting the jet winds may be launched in a relatively small region. This favors the X-wind model, that is, jets are launched in a small area near the inner disk edge.

ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP): A Forming Quadruple System with Continuum “Ribbons” and Intricate Outflows

One of the most poorly understood aspects of low-mass star formation is how multiple-star systems are formed. Here we present the results of Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 observations toward a forming quadruple protostellar system, G206.93-16.61E2, in the Orion B molecular cloud. ALMA 1.3 mm continuum emission reveals four compact objects, of which two are Class I young stellar objects and the other two are likely in prestellar phase. The 1.3 mm continuum emission also shows three asymmetric ribbon-like structures that are connected to the four objects, with lengths ranging from ∼500 to ∼2200 au. By comparing our data with magnetohydrodynamic simulations, we suggest that these ribbons trace accretion flows and also function as gas bridges connecting the member protostars. Additionally, ALMA CO J = 2−1 line emission reveals a complicated molecular outflow associated with G206.93-16.61E2, with arc-like structures suggestive of an outflow cavity viewed pole-on.

JWST Peers into the Class I Protostar TMC1A: Atomic Jet and Spatially Resolved Dissociative Shock Region

Outflows and winds launched from young stars play a crucial role in the evolution of protostars and the early stages of planet formation. However, the specific details of the mechanism behind these phenomena, including how they affect the protoplanetary disk structure, are still debated. We present JWST NIRSpec integral field unit observations of atomic and H2 lines from 1 to 5.1 μm toward the low-mass protostar TMC1A. For the first time, a collimated atomic jet is detected from TMC1A in the [Fe ii] line at 1.644 μm along with corresponding extended H2 2.12 μm emission. Toward the protostar, we detected spectrally broad H i and He i emissions with velocities up to 300 km s−1 that can be explained by a combination of protostellar accretion and a wide-angle wind. The 2 μm continuum dust emission, H i, He i, and O i all show emission from the illuminated outflow cavity wall and scattered line emission. These observations demonstrate the potential of JWST to characterize and reveal new information about the hot inner regions of nearby protostars; in this case, a previously undetected atomic wind and ionized jet in a well-known outflow.

Early Planet Formation in Embedded Disks (eDisk). III. A First High-resolution View of Submillimeter Continuum and Molecular Line Emission toward the Class 0 Protostar L1527 IRS

Studying the physical and chemical conditions of young embedded disks is crucial to constrain the initial conditions for planet formation. Here we present Atacama Large Millimeter/submillimeter Array observations of dust continuum at ∼0.″06 (8 au) resolution and molecular line emission at ∼0.″17 (24 au) resolution toward the Class 0 protostar L1527 IRS from the Large Program eDisk (Early Planet Formation in Embedded Disks). The continuum emission is smooth without substructures but asymmetric along both the major and minor axes of the disk as previously observed. The detected lines of 12CO, 13CO, C18O, H2CO, c-C3H2, SO, SiO, and DCN trace different components of the protostellar system, with a disk wind potentially visible in 12CO. The 13CO brightness temperature and the H2CO line ratio confirm that the disk is too warm for CO freezeout, with the snowline located at ∼350 au in the envelope. Both molecules show potential evidence of a temperature increase around the disk–envelope interface. SO seems to originate predominantly in UV-irradiated regions such as the disk surface and the outflow cavity walls rather than at the disk–envelope interface as previously suggested. Finally, the continuum asymmetry along the minor axis is consistent with the inclination derived from the large-scale (100″ or 14,000 au) outflow, but opposite to that based on the molecular jet and envelope emission, suggesting a misalignment in the system. Overall, these results highlight the importance of observing multiple molecular species in multiple transitions to characterize the physical and chemical environment of young disks.

Can Protostellar Outflows Set Stellar Masses?

The opening angles of some protostellar outflows appear too narrow to match the expected core–star mass efficiency (SFE) = 0.3–0.5, if the outflow cavity volume traces outflow mass, with a conical shape and a maximum opening angle near 90°. However, outflow cavities with a paraboloidal shape and wider angles are more consistent with observed estimates of the SFE. This paper presents a model of infall and outflow evolution based on these properties. The initial state is a truncated singular isothermal sphere which has mass ≈ 1 M ⊙, freefall time ≈ 80 kyr, and small fractions of magnetic, rotational, and turbulent energy. The core collapses pressure free as its protostar and disk launch a paraboloidal wide-angle wind. The cavity walls expand radially and entrain envelope gas into the outflow. The model matches the SFE values when the outflow mass increases faster than the protostar mass by a factor 1–2, yielding protostar masses typical of the IMF. It matches the observed outflow angles if the outflow mass increases at nearly the same rate as the cavity volume. The predicted outflow angles are then typically ∼50° as they increase rapidly through the stage 0 duration of ∼40 kyr. They increase more slowly up to ∼110° during their stage I duration of ∼70 kyr. With these outflow rates and shapes, the model predictions appear consistent with observational estimates of the typical stellar masses, SFEs, stage durations, and outflow angles, with no need for external mechanisms of core dispersal.

The Role of Outflow Feedback on Accretion of Compact Objects in Accretion Disk of Active Galactic Nuclei

Compact objects (COs) can exist and evolve in an active galactic nuclei (AGN) disk, triggering a series of attractive CO-related multimessenger events around a supermassive black hole. To better understand the nature of an embedded CO and its surroundings and to investigate CO-related events more accurately, in this paper, we study the specific accretion process of a CO in an AGN disk and explore the role of outflow feedback. We show that the asymptotically isotropic outflow generated from the CO hyper-Eddington accretion would truncate the circum-CO disk and push out its surrounding gas, resulting in recurrent formation and refilling of an outflow cavity to intermittently stop the accretion. Applying this universal cyclic process to black holes (BHs) and neutron stars (NSs), we find that, even if it is above the Eddington rate, the mass rate accreted onto a BH is dramatically reduced compared with the initial gas captured rate and thus consumes little mass of the AGN disk; outflow feedback on an NS is generally similar, but possesses complexities on the existence of a stellar magnetic field and hard surface. We demonstrate that although outflow feedback itself may be unobservable, it remarkably alters the CO evolution via reducing its mass growth rate, and the AGN disk can survive from the otherwise drastic CO accretion overlooking outflow. In addition, we discuss the potential influence of an underdense cavity on CO-related events, which embodies the significant role of outflow feedback as well.

FAUST – VIII. The protostellar disc of VLA 1623–2417W and its streamers imaged by ALMA

ABSTRACT More than 50 per cent of solar-mass stars form in multiple systems. It is therefore crucial to investigate how multiplicity affects the star and planet formation processes at the protostellar stage. We report continuum and C18O (2–1) observations of the VLA 1623–2417 protostellar system at 50 au angular resolution as part of the ALMA (Atacama Large Millimeter/submillimeter Array) Large Program FAUST. The 1.3 mm continuum probes the discs of VLA 1623A, B, and W, and the circumbinary disc of the A1 + A2 binary. The C18O emission reveals, for the first time, the gas in the disc envelope of VLA 1623W. We estimate the dynamical mass of VLA 1623W, Mdyn = 0.45 ± 0.08 M⊙, and the mass of its disc, Mdisc ∼ 6 × 10−3 M⊙. C18O also reveals streamers that extend up to 1000 au, spatially and kinematically connecting the envelope and outflow cavities of the A1 + A2 + B system with the disc of VLA 1623W. The presence of the streamers, as well as the spatial (∼1300 au) and velocity (∼2.2 km s−1) offsets of VLA 1623W, suggests that either sources W and A + B formed in different cores, interacting between them, or source W has been ejected from the VLA 1623 multiple system during its formation. In the latter case, the streamers may funnel material from the envelope and cavities of VLA 1623AB on to VLA 1623W, thus concurring to set its final mass and chemical content.

The SOUL view of IRAS 20126+4104

Context. We exploit the increased sensitivity of the recently installed adaptive optics SOUL at the LBT to obtain new high-spatial-resolution near-infrared images of the massive young stellar object IRAS20126+4104 and its outflow. Aims. We aim to derive the jet proper motions and kinematics, as well as to study its photometric variability by combining the novel performances of SOUL together with previous near-infrared images. Methods. We used both broad-band (Ks, K′) and narrow-band (Brγ, H2) observations from a number of near-infrared cameras (UKIRT/UFTI, SUBARU/CIAO, TNG/NICS, LBT/PISCES, and LBT/LUCI1) to derive maps of the continuum and the H2 emission in the 2.12 µm line. Three sets of images, obtained with adaptive optics (AO) systems (CIAO, in 2003; FLAO, in 2012; SOUL, in 2020), allowed us to derive the proper motions of a large number of H2 knots along the jet. Photometry from all images was used to study the jet variability. Results. We derived knot proper motions in the range of 1.7–20.3 mas yr−1 (i.e. 13–158 km s−1 at 1.64 kpc), implying an average outflow tangential velocity of ~80 km s−1. The derived knot dynamical age spans a ~200–4000 yr interval. A ring-like H2 feature near the protostar location exhibits peculiar kinematics and may represent the outcome of a wide-angle wind impinging on the outflow cavity. Both H2 geometry and velocities agree with those inferred from proper motions of the H2O masers, located at a smaller distance from the protostar. Although the total H2 line emission from the knots does not exhibit time variations at a ⪞0.3 mag level, we have found a clear continuum flux variation (radiation scattered by the dust in the cavity opened by the jet) which is anti-correlated between the blue-shifted and red-shifted lobes and may be periodic (with a period of ~12–18 yr). We suggest that the continuum variability might be related to inner-disc oscillations which have also caused the jet precession. Conclusions. Our analysis shows that multi-epoch high-spatial-resolution imaging in the near-infrared is a powerful tool to unveil the physical properties of highly embedded massive protostars.