Context. While planet formation is thought to occur early in the history of a protoplanetary disk, the presence of planets embedded in disks, or of other processes driving disk evolution, might be ...traced from their imprints on the disk structure. Aims. We study the morphology of the disk around the T Tauri star HD 143006, located in the ~5–11 Myr-old Upper Sco region, and we look for signatures of the mechanisms driving its evolution. Methods. We observed HD 143006 in polarized scattered light with VLT/SPHERE at near-infrared (J-band, 1.2 μm) wavelengths, reaching an angular resolution of ~0.037′′ (~6 au). We obtained two datasets, one with a 145 mas diameter coronagraph, and the other without, enabling us to probe the disk structure down to an angular separation of ~0.06′′ (~10 au). Results. In our observations, the disk of HD 143006 is clearly resolved up to ~0.5′′ and shows a clear large-scale asymmetry with the eastern side brighter than the western side. We detect a number of additional features, including two gaps and a ring. The ring shows an overbrightness at a position angle (PA) of ~140°, extending over a range in position angle of ~60°, and two narrow dark regions. The two narrow dark lanes and the overall large-scale asymmetry are indicative of shadowing effects, likely due to a misaligned inner disk. We demonstrate the remarkable resemblance between the scattered light image of HD 143006 and a model prediction of a warped disk due to an inclined binary companion. The warped disk model, based on the hydrodynamic simulations combined with three-dimensional radiative transfer calculations, reproduces all major morphological features. However, it does not account for the observed overbrightness at PA ~ 140°. Conclusions. Shadows have been detected in several protoplanetary disks, suggesting that misalignment in disks is not uncommon. However, the origin of the misalignment is not clear. As-yet-undetected stellar or massive planetary companions could be responsible for them, and naturally account for the presence of depleted inner cavities.
Full text
Available for:
FMFMET, NUK, UL, UM, UPUK
Vortices are one of the most promising mechanisms to locally concentrate millimeter dust grains and allow the formation of planetesimals through gravitational collapse. The outer disk around the ...binary system HD 142527 is known for its large horseshoe structure with azimuthal contrasts of ~3–5 in the gas surface density and of ~50 in the dust. Using
13
CO and C
18
O
J
= 3–2 transition lines, we detect kinematic deviations to the Keplerian rotation, which are consistent with the presence of a large vortex around the dust crescent, as well as a few spirals in the outer regions of the disk. Comparisons with a vortex model suggest velocity deviations up to 350 m s
−1
after deprojection compared to the background Keplerian rotation, as well as an extension of ±40 au radially and ~200° azimuthally, yielding an azimuthal-to-radial aspect ratio of ~5. Another alternative for explaining the vortex-like signal implies artificial velocity deviations generated by beam smearing in association with variations of the gas velocity due to gas pressure gradients at the inner and outer edges of the circumbinary disk. The two scenarios are currently difficult to differentiate and, for this purpose, would probably require the use of multiple lines at a higher spatial resolution. The beam smearing effect, due to the finite spatial resolution of the observations and gradients in the line emission, should be common in observations of protoplanetary disks and may lead to misinterpretations of the gas velocity, in particular around ring-like structures.
Full text
Available for:
FMFMET, NUK, UL, UM, UPUK
We present CARMA 1.3 mm continuum data of the disk surrounding the young brown dwarf 2MASS J044427+2512 in the Taurus molecular cloud. The high angular resolution of the CARMA observations (0."16) ...allows us to spatially resolve for the first time the thermal emission from dust around a brown dwarf. We analyze the interferometric visibilities and constrain the disk outer radius adopting disk models with power-law radial profiles of the dust surface density. In the case of a power-law index < or =, slant 1, we obtain a disk radius in the range of about 15-30 AU, while larger disks are inferred for steeper radial profiles. By combining this information on the disk spatial extent with the sub-mm spectral index of this source, we find conclusive evidence for mm-sized grains, or larger, in this brown dwarf disk. We discuss the implications of our results on the models of dust evolution in protoplanetary disks and brown dwarf formation.
Context. Grain growth in protoplanetary disks is the first step towards the formation of the rocky cores of planets. Models predict that grains grow, migrate, and fragment in the disk and predict ...varying dust properties as a function of radius, age, and physical properties. High-angular resolution observations at more than one (sub-)mm wavelength are the essential tool for constraining grain growth and migration on the disk midplane. Aims. We developed a procedure to analyze self-consistently multiwavelength (sub-)mm continuum interferometric observations of protoplanetary disks to constrain the radial distribution of dust properties. Methods. We apply this technique to existing multifrequency continuum mm observations of the disk around CQ Tau, a A8 pre-main sequence star with a well-studied disk. Results. We demonstrate that our models can be used to simultaneously constrain the disk and dust structure. In CQ Tau, the best-fitting model has a radial dependence of the maximum grain size, which decreases from a few cm in the inner disk (<40 AU) to a few mm at 80 AU. Nevertheless, the currently available dataset does not allow us to exclude the possibility of a uniform grain size distribution at a 3σ level.
Full text
Available for:
FMFMET, NUK, UL, UM, UPUK
Multi-wavelength observations of protoplanetary disks in the sub-millimeter continuum have measured spectral indices values which are significantly lower than what is found in the diffuse ...interstellar medium. Under the assumption that mm-wave emission of disks is mostly optically thin, these data have been generally interpreted as evidence for the presence of mm/cm-sized pebbles in the disk outer regions. In this work we investigate the effect of possible local optically thick regions on the mm-wave emission of protoplanetary disks without mm/cm-sized grains. A significant local increase of the optical depth in the disk can be caused by the concentration of solid particles, as predicted to result from a variety of proposed physical mechanisms. We calculate the filling factors and implied overdensities these optically thick regions would need to significantly affect the millimeter fluxes of disks, and we discuss their plausibility. We find that optically thick regions characterized by relatively small filling factors can reproduce the mm-data of young disks without requesting emission from mm/cm-sized pebbles. However, these optically thick regions require dust overdensities much larger than what predicted by any of the physical processes proposed in the literature to drive the concentration of solids. We find that only for the most massive disks it is possible and plausible to imagine that the presence of optically thick regions in the disk is responsible for the low measured values of the mm spectral index. For the majority of the disk population, optically thin emission from a population of large mm-sized grains remains the most plausible explanation. The results of this analysis further strengthen the scenario for which the measured low spectral indices of protoplanetary disks at mm wavelengths are due to the presence of large mm/cm-sized pebbles in the disk outer regions.
Full text
Available for:
FMFMET, NUK, UL, UM, UPUK
Context. Protoplanetary disks around young stars are the birth-sites of planets. Spectral energy distributions and direct images of a subset of disks known as transition disks reveal dust-depleted ...inner cavities. Some of these disks show asymmetric structures in thermal submillimetre emission and optical scattered light. These structures can be the result of planet(s) or companions embedded in the disk. Aims. We aim to detect and analyse the scattered light of the transition disk J160421.7-213028, identify disk structures, and compare the results with previous observations of this disk at other wavelengths. Methods. We obtained and analysed new polarised intensity observations of the transition disk J160421.7-213028 with VLT/SPHERE using the visible light instrument ZIMPOL at R′-band (0.626 μm). We probed the disk gap down to a radius of confidence of 0.1′′ (~15 AU at 145 pc). We interpret the results in the context of dust evolution when planets interact with the parental disk. Results. We observe a gap from 0.1 to 0.3′′ (~15 to 40 AU) and a bright annulus as previously detected by HiCIAO H-band observations at 1.65μm. The radial width of the annulus is around 40 AU, and its centre is at ~61 AU from the central star. The peak of the reflected light at 0.626 μm is located 20 AU inward of the cavity detected in the submillimetre. In addition, we detect a dip at a position angle of ~46.2 ± 5.4°. A dip was also detected with HiCIAO, but located at ~85°. If the dip observed with HiCIAO is the same, this suggests an average dip rotation of ~12°/year, which is inconsistent with the local Keplerian angular velocity of ~0.8°/yr at ~61 AU. Conclusions. The spatial discrepancy in the radial emission in J160421.7-213028 at different wavelengths is consistent with dust filtration at the outer edge of a gap carved by a massive planet. The dip rotation can be interpreted as fast variability of the inner disk and/or the presence of a warp or circumplanetary material of a planet at ~9.6 AU.
Full text
Available for:
FMFMET, NUK, UL, UM, UPUK
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.
Full text
Available for:
FMFMET, NUK, UL, UM, UPUK
BROWN DWARF DISKS WITH ALMA Ricci, L; Testi, L; NATTA, A ...
The Astrophysical journal,
08/2014, Volume:
791, Issue:
1
Journal Article
Peer reviewed
Open access
We present Atacama Large Millimeter/submillimeter Array continuum and spectral line data at 0.89 mm and 3.2 mm for three disks surrounding young brown dwarfs and very low mass stars in the Taurus ...star forming region. Dust thermal emission is detected and spatially resolved for all the three disks, while CO(J = 3-2) emission is seen in two disks. We analyze the continuum visibilities and constrain the disks' physical structure in dust. The results of our analysis show that the disks are relatively large; the smallest one has an outer radius of about 70 AU. The inferred disk radii, radial profiles of the dust surface density, and disk to central object mass ratios lie within the ranges found for disks around more massive young stars. We derive from our observations the wavelength dependence of the millimeter dust opacity. In all the three disks, data are consistent with the presence of grains with at least millimeter sizes, as also found for disks around young stars, and confirm that the early stages of the solid growth toward planetesimals occur also around very low-mass objects. We discuss the implications of our findings on models of solids evolution in protoplanetary disks, the main mechanisms proposed for the formation of brown dwarfs and very low-mass stars, as well as the potential of finding rocky and giant planets around very low-mass objects.
Context. To characterize the mechanisms of planet formation it is crucial to investigate the properties and evolution of protoplanetary disks around young stars, where the initial conditions for the ...growth of planets are set. The high spatial resolution of Atacama Large Millimeter/submillimeter Array (ALMA) and Karl G. Jansky Very Large Array (VLA) observations now allows the study of radial variations of dust properties in nearby resolved disks and the investigation of the early stages of grain growth in disk midplanes. Aims. Our goal is to study grain growth in the well-studied disk of the young, intermediate-mass star HD 163296 where dust processing has already been observed and to look for evidence of growth by ice condensation across the CO snowline, which has already been identified in this disk with ALMA. Methods. Under the hypothesis of optically thin emission, we compare images at different wavelengths from ALMA and VLA to measure the opacity spectral index across the disk and thus the maximum grain size. We also use a Bayesian tool based on a two-layer disk model to fit the observations and constrain the dust surface density. Results. The measurements of the opacity spectral index indicate the presence of large grains and pebbles (≥1 cm) in the inner regions of the disk (inside ~50 AU) and smaller grains, consistent with ISM sizes, in the outer disk (beyond 150 AU). Re-analyzing ALMA Band 7 science verification data, we find (radially) unresolved excess continuum emission centered near the location of the CO snowline at ~90 AU. Conclusions. Our analysis suggests a grain size distribution consistent with an enhanced production of large grains at the CO snowline and consequent transport to the inner regions. Our results combined with the excess in infrared scattered light suggests there is a structure at 90 AU involving the whole vertical extent of the disk. This could be evidence of small scale processing of dust at the CO snowline.
Full text
Available for:
FMFMET, NUK, UL, UM, UPUK
PDF
