ABSTRACT In recent years, spiral structures have been seen in scattered light observations and signs of vortices in millimeter images of protoplanetary disks, both probably linked with the presence ...of planets. We present Atacama Large Millimeter/submillimeter Array Band 7 (335 GHz or 0.89 mm) continuum observations of the transition disk HD 135344B at an unprecedented spatial resolution of 0 16, using superuniform weighting. The data show that the asymmetric millimeter-dust ring seen in previous work actually consists of an inner ring and an outer asymmetric structure. The outer feature is cospatial with the end of one of the spiral arms seen in scattered light, but the feature itself is not consistent with a spiral arm due to its coradiance. We propose a new possible scenario to explain the observed structures at both wavelengths. Hydrodynamical simulations show that a massive planet can generate a primary vortex (which dissipates at longer timescales, becoming an axisymmetric ring) and trigger the formation of a second generation vortex further out. Within this scenario, the two spiral arms observed at scattered light originate from a planet at ∼30 au and from the secondary vortex at ∼75 au rather than a planet further out as previously reported.
ABSTRACT
There is growing amount of very high resolution polarized scattered light images of circumstellar discs. Nascent giant planets are surrounded by their own circumplanetary discs that may ...scatter and polarize both the planetary and stellar light. Here, we investigate whether we could detect circumplanetary discs with the same technique and what can we learn from such detections. Here, we created scattered light mock observations at 1.245 microns (J band) for instruments like SPHERE and GPI, for various planetary masses (0.3, 1.0, 5.0, and 10.0 $\rm {\mathrm{ M}_{Jup}}$), disc inclinations (90, 60, 30, and 0 deg), and planet position angles (0, 45, and 90 deg). We found that the detection of a circumplanetary disc at 50 au from the star is significantly favoured if the planet is massive (${\ge} 5 \,\rm {\mathrm{ M}_{Jup}}$) and the system is nearly face-on (≤30°). In these cases, the accretion shock front on the surface of the circumplanetary discs is strong and bright enough to help the visibility of this subdisc. Its detection is hindered by the neighbouring circumstellar disc that also provides a strong polarized flux. However, the comparison between the PI and the Qϕ maps is a viable tool to pinpoint the presence of the circumplanetary disc within the circumstellar disc, as the two discs are behaving differently on those images.
Context. High-contrast scattered light observations have revealed the surface morphology of several dozen protoplanetary disks at optical and near-infrared wavelengths. Inclined disks offer the ...opportunity to measure part of the phase function of the dust grains that reside in the disk surface which is essential for our understanding of protoplanetary dust properties and the early stages of planet formation. Aims. We aim to construct a method which takes into account how the flaring shape of the scattering surface of an optically thick protoplanetary disk projects onto the image plane of the observer. This allows us to map physical quantities (e.g., scattering radius and scattering angle) onto scattered light images and retrieve stellar irradiation corrected images (r2-scaled) and dust phase functions. Methods. The scattered light mapping method projects a power law shaped disk surface onto the detector plane after which the observed scattered light image is interpolated backward onto the disk surface. We apply the method on archival polarized intensity images of the protoplanetary disk around HD 100546 that were obtained with VLT/SPHERE in the R′ band and VLT/NACO in the H and Ks bands. Results. The brightest side of the r2-scaled R′ band polarized intensity image of HD 100546 changes from the far to the near side of the disk when a flaring instead of a geometrically flat disk surface is used for the r2-scaling. The decrease in polarized surface brightness in the scattering angle range of ~40°–70° is likely a result of the dust phase function and degree of polarization which peak in different scattering angle regimes. The derived phase functions show part of a forward scattering peak, which indicates that large, aggregate dust grains dominate the scattering opacity in the disk surface. Conclusions. Projection effects of a protoplanetary disk surface need to be taken into account to correctly interpret scattered light images. Applying the correct scaling for the correction of stellar irradiation is crucial for the interpretation of the images and the derivation of the dust properties in the disk surface layer.
To date, nearly two hundred planet-forming disks have been imaged at high resolution. Our propensity to study bright and extended objects does, however, bias our view of the disk demography. In this ...work, we aim to help alleviate this bias by analyzing fifteen disks targeted with VLT/SPHERE that look faint in scattered light. Sources were selected based on a low far-infrared excess from the spectral energy distribution. The comparison with the ALMA images available for a few sources shows that the scattered light surveyed by these datasets is only detected from a small portion of the disk extent. The mild anticorrelation between the disk brightness and the near-infrared excess demonstrates that these disks are self-shadowed: the inner disk rim intercepts much starlight and leaves the outer disk in penumbra. Based on the uniform distribution of the disk brightness in scattered light across all spectral types, self-shadowing would act similarly for inner rims at a different distance from the star. We discuss how the illumination pattern of the outer disk may evolve with time. Some objects in the sample are proposed to be at an intermediate stage toward bright disks from the literature, with either no shadow or with signs of azimuthally confined shadows.
Planet-forming disks are not isolated systems. Their interaction with the surrounding medium affects their mass budget and chemical content. In the context of the ALMA-DOT program, we obtained ...high-resolution maps of assorted lines from six disks that are still partly embedded in their natal envelope. In this work, we examine the SO and SO2 emission that is detected from four sources: DG Tau, HL Tau, IRAS 04302+2247, and T Tau. The comparison with CO, HCO+, and CS maps reveals that the SO and SO2 emission originates at the intersection between extended streamers and the planet-forming disk. Two targets, DG Tau and HL Tau, offer clear cases of inflowing material inducing an accretion shock on the disk material. The measured rotational temperatures and radial velocities are consistent with this view. In contrast to younger Class 0 sources, these shocks are confined to the specific disk region impacted by the streamer. In HL Tau, the known accreting streamer induces a shock in the disk outskirts, and the released SO and SO2 molecules spiral toward the star in a few hundred years. These results suggest that shocks induced by late accreting material may be common in the disks of young star-forming regions with possible consequences for the chemical composition and mass content of the disk. They also highlight the importance of SO and SO2 line observations in probing accretion shocks from a larger sample.
Context.
Shadows in scattered light images of protoplanetary disks are a common feature and support the presence of warps or misalignments between disk regions. These warps are possibly caused by an ...inclined (sub-)stellar companion embedded in the disk.
Aims.
We aim to study the morphology of the protoplanetary disk around the Herbig Ae star HD 139614 based on the first scattered light observations of this disk, which we model with the radiative transfer code
MCMax3D
.
Methods.
We obtained
J
- and
H
-band observations that show strong azimuthal asymmetries in polarized scattered light with VLT/SPHERE. In the outer disk, beyond ~30 au, a broad shadow spans a range of ~240 deg in position angle, in the east. A bright ring at ~16 au also shows an azimuthally asymmetric brightness, with the faintest side roughly coincidental with the brightest region of the outer disk. Additionally, two arcs are detected at ~34 and ~50 au. We created a simple four-zone approximation to a warped disk model of HD 139614 in order to qualitatively reproduce these features. The location and misalignment of the disk components were constrained from the shape and location of the shadows they cast.
Results.
We find that the shadow on the outer disk covers a range of position angles too wide to be explained by a single inner misaligned component. Our model requires a minimum of two separate misaligned zones – or a continuously warped region – to cast this broad shadow on the outer disk. A small misalignment of ~4° between adjacent components can reproduce most of the observed shadow features.
Conclusions.
Multiple misaligned disk zones, potentially mimicking a warp, can explain the observed broad shadows in the HD 139614 disk. A planetary mass companion in the disk, located on an inclined orbit, could be responsible for such a feature and for the dust-depleted gap responsible for a dip in the SED.
Context. The mechanisms governing planet formation are not fully understood. A new era of high-resolution imaging of protoplanetary disks has recently started, thanks to new instruments such as ...SPHERE, GPI, and ALMA. The planet formation process can now be directly studied by imaging both planetary companions embedded in disks and their effect on disk morphology. Aims. We image disk features that could be potential signs of planet-disk interaction with unprecedented spatial resolution and sensitivity. Two companion candidates have been claimed in the disk around the young Herbig Ae/Be star HD 100546. Thus, this object serves as an excellent target for our investigation of the natal environment of giant planets. Methods. We exploit the power of extreme adaptive optics operating in conjunction with the new high-contrast imager SPHERE to image HD 100546 in scattered light. We obtained the first polarized light observations of this source in the visible (with resolution as fine as 2 AU) and new H and K band total intensity images that we analyzed with the pynpoint package. Results. The disk shows a complex azimuthal morphology, where multiple scattering of photons most likely plays an important role. High brightness contrasts and arm-like structures are ubiquitous in the disk. A double-wing structure (partly due to angular differential imaging processing) resembles a morphology newly observed in inclined disks. Given the cavity size in the visible (11 AU), the CO emission associated to the planet candidate c might arise from within the circumstellar disk. We find an extended emission in the K band at the expected location of b. The surrounding large-scale region is the brightest in scattered light. There is no sign of any disk gap associated to b.
Context. Dozens of protoplanetary disks have been imaged in scattered light during the last decade. Aims. The variety of brightness, extension, and morphology from this census motivates a taxonomical ...study of protoplanetary disks in polarimetric light to constrain their evolution and establish the current framework of this type of observation. Methods. We classified 58 disks with available polarimetric observations into six major categories (Ring, Spiral, Giant, Rim, Faint, and Small disks) based on their appearance in scattered light. We re-calculated the stellar and disk properties from the newly available Gaia DR2 and related these properties with the disk categories. Results. More than half of our sample shows disk substructures. For the remaining sources, the absence of detected features is due to their faintness, their small size, or the disk geometry. Faint disks are typically found around young stars and typically host no cavity. There is a possible dichotomy in the near-infrared (NIR) excess of sources with spiral-disks (high) and ring-disks (low). Like spirals, shadows are associated with a high NIR excess. If we account for the pre-main sequence evolutionary timescale of stars with different mass, spiral arms are likely associated with old disks. We also found a loose, shallow declining trend for the disk dust mass with time. Conclusions. Protoplanetary disks may form substructures like rings very early in their evolution but their detectability in scattered light is limited to relatively old sources ( ≳5 Myr) where the recurrently detected disk cavities cause the outer disk to be illuminate. The shallow decrease of disk mass with time might be due to a selection effect, where disks observed thus far in scattered light are typically massive, bright transition disks with longer lifetimes than most disks. Our study points toward spirals and shadows being generated by planets of a fraction of a Jupiter mass to a few Jupiter masses in size that leave their (observed) imprint on both the inner disk near the star and the outer disk cavity.
Abstract
We present new Very Large Array observations, between 6.8 and 66 mm, of the edge-on Class I disk IRAS04302+2247. Observations at 6.8 mm and 9.2 mm lead to the detection of thermal emission ...from the disk, while shallow observations at the other wavelengths are used to correct for emission from other processes. The disk radial brightness profile transitions from broadly extended in previous Atacama Large Millimeter/submillimeter Array 0.9 mm and 2.1 mm observations to much more centrally brightened at 6.8 mm and 9.2 mm, which can be explained by optical depth effects. The radiative transfer modeling of the 0.9 mm, 2.1 mm, and 9.2 mm data suggests that the grains are smaller than 1 cm in the outer regions of the disk, allowing us to obtain the first lower limit for the scale height of grains emitting at millimeter wavelengths in a protoplanetary disk. We find that the millimeter dust scale height is between 1 au and 6 au at a radius 100 au from the central star, while the gas scale height is estimated to be about 7 au, indicating a modest level of settling. The estimated dust height is intermediate between less evolved Class 0 sources, which are found to be vertically thick, and more evolved Class II sources, which show a significant level of settling. This suggests that we are witnessing an intermediate stage of dust settling.
Context. The study of dynamical processes in protoplanetary disks is essential to understand planet formation. In this context, transition disks are prime targets because they are at an advanced ...stage of disk clearing and may harbor direct signatures of disk evolution. Aims. We aim to derive new constraints on the structure of the transition disk MWC 758, to detect non-axisymmetric features and understand their origin. Methods. We obtained infrared polarized intensity observations of the protoplanetary disk MWC 758 with VLT/SPHERE at 1.04 μm to resolve scattered light at a smaller inner working angle (0.093′′) and a higher angular resolution (0.027′′) than previously achieved. Results. We observe polarized scattered light within 0.53′′ (148 au) down to the inner working angle (26 au) and detect distinct non-axisymmetric features but no fully depleted cavity. The two small-scale spiral features that were previously detected with HiCIAO are resolved more clearly, and new features are identified, including two that are located at previously inaccessible radii close to the star. We present a model based on the spiral density wave theory with two planetary companions in circular orbits. The best model requires a high disk aspect ratio (H/r ~ 0.20 at the planet locations) to account for the large pitch angles which implies a very warm disk. Conclusions. Our observations reveal the complex morphology of the disk MWC 758. To understand the origin of the detected features, the combination of high-resolution observations in the submillimeter with ALMA and detailed modeling is needed.
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