We present ALMA 12-m, 7-m Total Power (TP) Array observations of the FU Orionis outbursting system, covering spatial scales ranging from 160 to 25,000 au. The high-resolution interferometric data reveals an elongated ^12CO(2-1) feature previously observed at lower resolution in ^12CO(3-2). Kinematic modeling indicates that this feature can be interpreted as an accretion streamer feeding the binary system. The mass infall rate provided by the streamer is significantly lower than the typical stellar accretion rates (even in quiescent states), suggesting that this streamer alone is not massive enough to sustain the enhanced accretion rates characteristic of the outbursting class prototype. The observed streamer may not be directly linked to the current outburst but rather a remnant of a previous, more massive streamer that may have contributed enough to the disk mass to render it unstable and trigger FU Ori's outburst. The new data detects, for the first time, a vast, slow-moving carbon monoxide molecular outflow emerging from this object. To accurately assess the outflow properties (mass, momentum, kinetic energy), we employed ^13CO(2-1) data to correct for optical depth effects. The analysis indicates that the outflow corresponds to swept-up material not associated with the current outburst, similar to slow-molecular outflows observed around other FUor and Class I protostellar objects.

Eruptive stars are a class of young stellar objects that show an abrupt increase in their luminosity. These burst-like episodes are thought to dominate the stellar accretion process during the class 0/class I stage. We present an overview of a survey of seven episodically accreting protostars aimed at studying their potentially complex circumstellar surroundings. The observations were performed with the instrument SPHERE, mounted at the VLT. We observed the eruptive stars in H-band with the near-infrared imager IRDIS and used the polarimeter to extract the polarized light scattered from the stars' surroundings. We produced polarized light images for three FUor objects, Z CMa, V960 Mon, and FU Ori, and four EXor objects, XZ Tau, UZ Tau, NY Ori, and EX Lup. We calculated the intrinsic polarization fraction for all the observed stars. In all systems we registered scattered light from around the primary star. FU Ori and V960 Mon are surrounded by complex structures including spiral-like features. In Z CMa, we detected a point source 0.7 arcsec to the northeast of the primary. Based on the astrometric measurements from archival Keck/NIRC2 data, we find this source to be a third member of the system. Further, Z CMa displays an outflow extending thousands of au. Unlike the other EXor objects in our sample, XZ Tau shows bright, extended scattered light structures, also associated with an outflow on a scale of hundreds of au. The other EXors show relatively faint disk-like structures in the immediate vicinity of the coronagraph. Asymmetric arms were only found around FUor objects, while faint disks seem to predominantly occur around EXors. Importantly, for Z CMa the detection of the faint extended structure questions previous interpretations of the system's dynamic state. The streamer which was associated with a fly-by object turned out to be part of a huge outflow extending 6000 au.

The sample of planet-forming disks observed by high-contrast imaging campaigns over the last decade is mature enough to enable the demographical analysis of individual star-forming regions. We present the full census of Taurus sources with VLT/SPHERE polarimetric images available. The whole sample sums up to 43 targets (of which 31 have not been previously published) corresponding to one-fifth of the Class II population in Taurus and about half of such objects that are observable. A large fraction of the sample is apparently made up of isolated faint disks (equally divided between small and large self-shadowed disks). Ambient signal is visible in about one-third of the sample. This probes the interaction with the environment and with companions or the outflow activity of the system. The central portion of the Taurus region almost exclusively hosts faint disks, while the periphery also hosts bright disks interacting with their surroundings. The few bright disks are found around apparently older stars. The overall picture is that the Taurus region is in an early evolutionary stage of planet formation. Yet, some objects are discussed individually, as in an intermediate or exceptional stage of the disk evolution. This census provides a first benchmark for the comparison of the disk populations in different star forming regions.

Dense stellar environments as hosts of ongoing star formation increase the probability of gravitational encounters among stellar systems during the early stages of evolution. Stellar interaction may occur through non-recurring, hyperbolic or parabolic passages (a so-called 'fly-by'), through secular binary evolution, or through binary capture. In all three scenarios, the strong gravitational perturbation is expected to manifest itself in the disc structures around the individual stars. Here, we present near-infrared polarised light observations that were taken with the SPHERE/IRDIS instrument of three known interacting twin-disc systems: AS 205, EM* SR 24, and FU Orionis. The scattered light exposes spirals likely caused by the gravitational interaction. On a larger scale, we observe connecting filaments between the stars. We analyse their very complex polarised intensity and put particular attention to the presence of multiple light sources in these systems. The local angle of linear polarisation indicates the source whose light dominates the scattering process from the bridging region between the two stars. Further, we show that the polarised intensity from scattering with multiple relevant light sources results from an incoherent summation of the individuals' contribution. This can produce nulls of polarised intensity in an image, as potentially observed in AS 205. We discuss the geometry and content of the systems by comparing the polarised light observations with other data at similar resolution, namely with ALMA continuum and gas emission. Collective observational data can constrain the systems' geometry and stellar trajectories, with the important potential to differentiate between dynamical scenarios of stellar interaction.

The formation of giant planets has traditionally been divided into two pathways: core accretion and gravitational instability. However, in recent years, gravitational instability has become less favored, primarily due to the scarcity of observations of fragmented protoplanetary disks around young stars and the low occurrence rate of massive planets on very wide orbits. In this study, we present a SPHERE/IRDIS polarized light observation of the young outbursting object V960 Mon. The image reveals a vast structure of intricately shaped scattered light with several spiral arms. This finding motivated a reanalysis of archival Atacama Large Millimeter/submillimeter Array 1.3 mm data acquired just two years after the onset of the outburst of V960 Mon. In these data, we discover several clumps of continuum emission aligned along a spiral arm that coincides with the scattered light structure. We interpret the localized emission as fragments formed from a spiral arm under gravitational collapse. Estimating the mass of solids within these clumps to be of several Earth masses, we suggest this observation to be the first evidence of gravitational instability occurring on planetary scales. This study discusses the significance of this finding for planet formation and its potential connection with the outbursting state of V960 Mon.

We present ALMA multiwavelength observations of the protoplanetary disk around the nearby (d$\sim$100 pc) young solar analog MP Mus (PDS 66). These observations at 0.89 mm, 1.3 mm, and 2.2 mm have angular resolutions of $\sim$ 1", 0.05", and 0.25", respectively, and probe the dust and gas in the system with unprecedented detail and sensitivity. The disk appears smooth down to the 4 au resolution of the 1.3 mm observations, in contrast with most disks observed at comparable spatial scales. The dust disk has a radius of 60$\pm$5 au, a dust mass of $0.14_{-0.06}^{+0.11} M_{\rm Jup}$, and a mm spectral index $<2$ in the inner 30 au, suggesting optically thick emission from grains with high albedo in this region. Several molecular gas lines are also detected extending up to 130$\pm$15 au, similar to small grains traced by scattered light observations. Comparing the fluxes of different CO isotopologues with previous models yields a gas mass of $0.1-1 M_{\rm Jup}$, implying a gas to dust ratio of 1-10. We also measure a dynamical stellar mass of $M_{\rm dyn}$=1.30$\pm$0.08 $M_\odot$ and derive an age of 7-10 Myr for the system. The survival of large grains in an evolved disk without gaps/rings is surprising, and it is possible that existing substructures remain undetected due to optically thick emission at 1.3 mm. Alternatively, small structures may still remain unresolved with the current observations. Based on simple scaling relations for gap-opening planets and gap widths, this lack of substructures places upper limits to the masses of planets in the disk as low as 2 $M_\oplus$-0.06 $M_{\rm Jup}$ at $r > 40$ au. The lack of mm emission at radii $r > 60$ au also suggests that the gap in scattered light between 30-80 au is likely not a gap in the disk density, but a shadow cast by a puffed-up inner disk.

ABSTRACT Warps have often been used to explain disc properties, but well-characterized examples are important due to their role in disc evolution. Scattered light images of discs with central gaps have revealed sharp warps, such that the outer rings are shadowed by tilted inner discs. The near-infrared intensity drops along the ring around T-Tauri star DoAr 44 have been interpreted in terms of a central warp. We report new ALMA observations of DoAr 44 in the continuum at 230 and 350 GHz (at ∼10 au), along with a new epoch of Spectro Polarimetric High-contrast Exoplanet REsearch (SPHERE)/Infrared Dual-band Imager and Spectrograph differential polarized imaging taken during excellent weather conditions. The ALMA observations resolve the ring and confirm the decrements proposed from deconvolution of coarse 336 GHz data. The scattered light image constrains the dips, which correspond to a misaligned inner disc with a relative inclination ξ = 21.4 $^{+6.7}_{-8.3}$ deg. The SPHERE intensity profile shows a morphological change compared to a previous epoch that may be interpreted as a variable orientation of the inner disc, from ξ ∼ 30 deg to ξ ∼ 20 deg. The intensity dips probably correspond to temperature decrements, as their mm-spectral index, $\alpha ^{230 \textrm {GHz}}_{350 \textrm {GHz}} \sim$ 2.0 ± 0.1, is indicative of optically thick emission. The azimuth of the two temperature decrements are leading clockwise relative to the infrared-dips, by η = 14.95 deg and η = 7.92 deg. For a retrograde disc, such shifts are expected from a thermal lag and imply gas surface densities of Σg = 117 ± 10 g cm−2 and Σg = 48 ± 10 g cm−2. A lopsided disc, with contrast ratio fr = 2.4 ± 0.5, is also consistent with the large continuum crescent.

The interpretation of molecular-line data using hydrodynamical simulations of planet–disk interactions fosters new hope for the indirect detection of protoplanets. In a model-independent approach, embedded protoplanets should be found at the roots of abrupt Doppler flips in velocity centroid maps. However, the largest velocity perturbation known for an unwarped disk, in the disk of HD 100546, leads to a conspicuous Doppler flip that coincides with a thick dust ring, in contradiction with an interpretation in terms of a ≳1 M jup body. Here we present new ALMA observations of the 12CO(2–1) kinematics in HD 100546, with a factor of 2 finer angular resolutions. We find that the disk rotation curve is consistent with a central mass 2.1 < M ⋆/M ⊙ < 2.3 and that the blueshifted side of the Doppler flip is due to vertical motions, reminiscent of the disk wind proposed previously from blueshifted SO lines. We tentatively propose a qualitative interpretation in terms of a surface disturbance to the Keplerian flow, i.e., a disk eruption, driven by an embedded outflow launched by a ∼10 M earth body. Another interpretation involves a disk-mass-loading hot spot at the convergence of an envelope accretion streamer.

Recent imaging of the disc around the V4046Sgr spectroscopic binary revealed concentric regions of dust rings and gaps. The object's proximity and expected equilibrated state due to its old age (>20Myr) make it a superb testbed for hydrodynamical studies in direct comparison to observations. We employ two-dimensional hydrodynamical simulations of gas and multiple dust species to test whether the observed structure conforms with the presence of giant planets embedded in the disc. We then perform radiative transfer calculations of sky images, which we filter for the telescope response for comparison with near-infrared and millimetre observations. We find that the existing data are in excellent agreement with a flared disc and the presence of two giant planets, at 9au and 20au, respectively. The different ring widths are recovered by diffusion-balanced dust trapping within the gas pressure maxima. In our radiative transfer model, the diffusion in vertical direction is reduced in comparison to the radial value by a factor of five to recover the spectral energy distribution. Further, we report a previously unaddressed, azimuthally-confined intensity decrement on the bright inner ring in the near-infrared scattered light observation. Our model shows that this decrement can be explained by a shadow cast by a circumplanetary disc around the same giant planet that creates the inner cavity in the hydrodynamical simulations. We examine the shape of the intensity indentation and discuss the potential characterisation of a giant planet and its associated disc by its projected shadow in scattered light observations.

The nearby V4046 Sgr spectroscopic binary hosts a gas-rich disc known for its wide cavity and dusty ring. We present high resolution (∼20 mas or 1.4 au) ALMA observations of the 1.3mm continuum of V4046 Sgr which, combined with SPHERE–IRDIS polarised images and a well-sampled spectral energy distribution (SED), allow us to propose a physical model using radiative transfer (RT) predictions. The ALMA data reveal a thin ring at a radius of 13.15±0.42 au (Ring13), with a radial width of 2.46±0.56 au. Ring13 is surrounded by a ∼10 au-wide gap, and it is flanked by a mm-bright outer ring (Ring24) with a sharp inner edge at 24 au. Between 25 and ∼35 au the brightness of Ring24 is relatively flat and then breaks into a steep tail that reaches out to ∼60 au. In addition, central emission is detected close to the star which we interpret as a tight circumbinary ring made of dust grains with a lower size limit of 0.8 mm at 1.1 au. In order to reproduce the SED, the model also requires an inner ring at ∼5 au (Ring5) composed mainly of small dust grains, hiding under the IRDIS coronagraph, and surrounding the inner circumbinary disc. The surprisingly thin Ring13 is nonetheless roughly 10 times wider than its expected vertical extent. The strong near-far disc asymmetry at 1.65 μm points at a very forward-scattering phase function and requires grain radii of no less than 0.4 μm.

Context. High-resolution ALMA observations such as the DSHARP campaign have revealed a variety of rich substructures in numerous protoplanetary disks. These structures consist of rings, gaps, and asymmetric features. It has been debated whether planets can be accounted for among these substructures in the dust continuum. Characterizing the origin of asymmetries, as seen in HD 163296, might lead to a better understanding of planet formation and the underlying physical parameters of the system. Aims. We test the possibility that the formation of the crescent-shaped asymmetry in the HD 163296 disk can be attributed to planet-disk interaction. The goal is to obtain constraints on planet masses, eccentricities, and disk viscosities. Furthermore, we test the reproducibility of the two prominent rings in the HD 163296 disk at 67 and 100 au. Methods. We performed two-dimensional, multi-fluid, hydrodynamical simulations with the FARGO3D code, including three embedded planets in the setup. Dust is described via the pressureless fluid approach and distributed over eight size bins. The resulting grids were post-processed with the radiative transfer code RADMC-3D and CASA software to model the synthetic observations. Results. We find that the crescent-shaped asymmetry can be qualitatively modeled with a Jupiter mass planet at a radial distance of 48 au. Dust is trapped in the trailing Lagrange point L5, preferably, with a mass of between 10 and 15 earth masses. The observation of such a feature constrains the level of viscosity and planetary mass. Increased values of eccentricity of the innermost Jupiter mass planet negatively impacts the stability of the crescent-shaped feature and does not reproduce the observed radial proximity to the first prominent ring in the system. Generally, a low level of viscosity (α ≤ 2 × 10−3) is necessary to allow for the existence of such a feature. Including dust feedback in the leading point, L4, can dominantly capture dust for dust grains with an initial Stokes number ≤ 3.6 × 10−2. In the synthetic ALMA observation of the model with dust feedback, two crescent-shaped features are visible. The observational results suggest a negligible effect on the part of dust feedback since only one such feature has been detected so far. The dust-to-gas ratio may thus be overestimated in the models. Additionally, the planet mass growth time scale does not strongly affect the formation of such asymmetries in the co-orbital region.

Context. In recent years, protoplanetary disks with spiral structures have been detected in scattered light, millimeter continuum, and CO gas emission. The mechanisms causing these structures are still under debate. A popular scenario to drive the spiral arms is the one of a planet perturbing the material in the disk. However, if the disk is massive, gravitational instability is usually the favored explanation. Multiwavelength studies could be helpful to distinguish between the two scenarios. So far, only a handful of disks with spiral arms have been observed in both scattered light and millimeter continuum. Aims. We aim to perform an in-depth characterization of the protoplanetary disk morphology around WaOph 6 analyzing data obtained at different wavelengths, as well as to investigate the origin of the spiral features in the disk. Methods. We present the first near-infrared polarimetric observations of WaOph 6 obtained with SPHERE at the VLT and compare them to archival millimeter continuum ALMA observations. We traced the spiral features in both data sets and estimated the respective pitch angles. We discuss the different scenarios that can give rise to the spiral arms in WaOph 6. We tested the planetary perturber hypothesis by performing hydrodynamical and radiative transfer simulations to compare them with scattered light and millimeter continuum observations. Results. We confirm that the spiral structure is present in our polarized scattered light H-band observations of WaOph 6, making it the youngest disk with spiral arms detected at these wavelengths. From the comparison to the millimeter ALMA-DSHARP observations, we confirm that the disk is flared. We explore the possibility of a massive planetary perturber driving the spiral arms by running hydrodynamical and radiative transfer simulations, and we find that a planet of minimum 10 MJup outside of the observed spiral structure is able to drive spiral arms that resemble the ones in the observations. We derive detection limits from our SPHERE observations and get estimates of the planet’s contrast from different evolutionary models. Conclusions. Up to now, no spiral arms had been observed in scattered light in disks around K and/or M stars with ages <1 Myr. Future observations of WaOph 6 could allow us to test theoretical predictions for planet evolutionary models, as well as give us more insight into the mechanisms driving the spiral arms.

ABSTRACT Planet–disc interactions build up local pressure maxima that may halt the radial drift of protoplanetary dust, and pile it up in rings and crescents. ALMA observations of the HD 135344B disc revealed two rings in the thermal continuum stemming from ∼mm-sized dust. At higher frequencies the inner ring is brighter relative to the outer ring, which is also shaped as a crescent rather than a full ring. In near-IR scattered light images, the disc is modulated by a two-armed grand-design spiral originating inside the ALMA inner ring. Such structures may be induced by a massive companion evacuating the central cavity, and by a giant planet in the gap separating both rings, that channels the accretion of small dust and gas through its filamentary wakes while stopping the larger dust from crossing the gap. Here we present ALMA observations in the J = (2 − 1) CO isotopologue lines and in the adjacent continuum, with up to 12 km baselines. Angular resolutions of ∼0${_{.}^{\prime\prime}}$03 reveal the tentative detection of a filament connecting both rings, and which coincides with a local discontinuity in the pitch angle of the IR spiral, proposed previously as the location of the protoplanet driving this spiral. Line diagnostics suggests that turbulence, or superposed velocity components, is particularly strong in the spirals. The 12CO(2-1) 3D rotation curve points at stellocentric accretion at radii within the inner dust ring, with a radial velocity of up to ${\sim}5{{\ \rm per\ cent}}\pm 0.5{{\ \rm per\ cent}}$ Keplerian, which corresponds to an excessively large accretion rate of ${\sim}2\times 10^{-6}\, M_\odot \,$yr−1 if all of the CO layer follows the 12CO(2-1) kinematics. This suggests that only the surface layers of the disc are undergoing accretion, and that the line broadening is due to superposed laminar flows.

Jupiter and Saturn formed early, before the gas disk dispersed. The presence of gap-opening planets affects the dynamics of the gas and embedded solids and halts the inward drift of grains above a certain size. A drift barrier can explain the absence of calcium–aluminum-rich inclusions (CAIs) in chondrites originating from parent bodies that accreted in the inner solar system. Employing an interdisciplinary approach, we use a μ-X-ray-fluorescence scanner to search for large CAIs and a scanning electron microscope to search for small CAIs in the ordinary chondrite NWA 5697. We carry out long-term, two-dimensional simulations including gas, dust, and planets to characterize the transport of grains within the viscous α-disk framework exploring the scenarios of a stand-alone Jupiter, Jupiter and Saturn in situ, or Jupiter and Saturn in a 3:2 resonance. In each case, we find a critical grain size above which drift is halted as a function of the physical conditions in the disk. From the laboratory search we find four CAIs with a largest size of ≈200 μm. Combining models and data, we provide an estimate for the upper limit of the α-viscosity and the surface density at the location of Jupiter, using reasonable assumptions about the stellar accretion rate during inward transport of CAIs, and assuming angular momentum transport to happen exclusively through viscous effects. Moreover, we find that the compound gap structure in the presence of Saturn in a 3:2 resonance favors inward transport of grains larger than CAIs currently detected in ordinary chondrites.

The migration of planetary cores embedded in a protoplanetary disk is an important mechanism within planet-formation theory, relevant for the architecture of planetary systems. Consequently, planet migration is actively discussed, yet often results of independent theoretical or numerical studies are unconstrained due to the lack of observational diagnostics designed in light of planet migration. In this work we follow the idea of inferring the migration behavior of embedded planets by means of the characteristic radial structures that they imprint in the disk's dust density distribution. We run hydrodynamical multifluid simulations of gas and several dust species in a locally isothermal alpha-disk in the low-viscosity regime (alpha = 10(-5)) and investigate the obtained dust structures. In this framework, a planet of roughly Neptune mass can create three (or more) rings in which dust accumulates. We find that the relative spacing of these rings depends on the planet's migration speed and direction. By performing subsequent radiative transfer calculations and image synthesis we show that-always under the condition of a near-inviscid disk-different migration scenarios are, in principle, distinguishable by long-baseline, state-of-the-art Atacama Large Millimeter/submillimeter Array observations.

Aerodynamic theory predicts that dust grains in protoplanetary disks will drift radially inward on comparatively short timescales. In this context, it has long been known that the presence of a gap opened by a planet can significantly alter the dust dynamics. In this paper, we carry out a systematic study employing long-term numerical simulations aimed at characterizing the critical particle size for retention outside a gap as a function of particle size, as well as various key parameters defining the protoplanetary disk model. To this end, we perform multifluid hydrodynamical simulations in two dimensions, including different dust species, which we treat as pressureless fluids. We initialize the dust outside of the planet’s orbit and study under which conditions dust grains are able to cross the gap carved by the planet. In agreement with previous work, we find that the permeability of the gap depends both on dust dynamical properties and the gas disk structure: while small dust follows the viscously accreting gas through the gap, dust grains approaching a critical size are progressively filtered out. Moreover, we introduce and compute a depletion factor that enables us to quantify the way in which higher viscosity, smaller planet mass, or a more massive disk can shift this critical size to larger values. Our results indicate that gap-opening planets may act to deplete the inner reaches of protoplanetary disks of large dust grains—potentially limiting the accretion of solids onto forming terrestrial planets.