On the cavity of a debris disc carved by a giant planet

On the cavity of a debris disc carved by a giant planet


Authors:

Regály et al

Abstract:
One possible explanation of the cavity in debris discs is the gravitational perturbation of an embedded giant planet. Planetesimals passing close to a massive body are dynamically stirred resulting in a cleared region known as the chaotic zone. Theory of overlapping mean-motion resonances predicts the width of this cavity. To test whether this cavity is identical to the chaotic zone, we investigate the formation of cavities by means of collisionless N-body simulations assuming a 1.25–10 Jupiter mass planet with eccentricities of 0–0.9. Synthetic images at millimetre wavelengths are calculated to determine the cavity properties by fitting an ellipse to 14 per cent contour level. Depending on the planetary eccentricity, epl, the elliptic cavity wall rotates as the planet orbits with the same (epl less than 0.2) or half (epl greater than 0.2) period that of the planet. The cavity centre is offset from the star along the semimajor axis of the planet with a distance of d=0.1q−0.17e0.5pl d=0.1q−0.17epl0.5 in units of cavity size towards the planet's orbital apocentre, where q is the planet-to-star mass ratio. Pericentre (apocentre) glow develops for epl less than 0.05 (epl greater than 0.1), while both are present for 0.05 ≤ epl ≤ 0.1. Empirical formulae are derived for the sizes of the cavities: δacav = 2.35q0.36 and
δacav=7.87q0.37e0.38pl δacav=7.87q0.37epl0.38 for epl ≤ 0.05 and epl greater 0.05, respectively. The cavity eccentricity, ecav, equals to that of the planet only for 0.3 ≤ epl ≤ 0.6. A new method based on Atacama Large Millimeter/submillimeter Array observations for estimating the orbital parameters and mass of the planet carving the cavity is also given.

A Direct Imaging Survey of Spitzer detected debris disks: Occurrence of giant planets in dusty systems

A Direct Imaging Survey of Spitzer detected debris disks: Occurrence of giant planets in dusty systems

Authors:

Meshkat et al

Abstract:

We describe a joint high contrast imaging survey for planets at Keck and VLT of the last large sample of debris disks identified by the Spitzer Space Telescope. No new substellar companions were discovered in our survey of 30 Spitzer-selected targets. We combine our observations with data from four published surveys to place constraints on the frequency of planets around 130 debris disk single stars, the largest sample to date. For a control sample, we assembled contrast curves from several published surveys targeting 277 stars which do not show infrared excesses. We assumed a double power law distribution in mass and semi-major axis of the form f(m,a) = Cmαaβ, where we adopted power law values and logarithmically flat values for the mass and semi-major axis of planets. We find that the frequency of giant planets with masses 5-20 MJup and separations 10-1000 AU around stars with debris disks is 6.27% (68% confidence interval 3.68 - 9.76%), compared to 0.73% (68% confidence interval 0.20 - 1.80%) for the control sample of stars without disks. These distributions differ at the 88% confidence level, tentatively suggesting distinctness of these samples.

Inferring giant planets from ALMA mm continuum and line observations in (transition) disks

Inferring giant planets from ALMA mm continuum and line observations in (transition) disks 

Authors:

Facchini et al

Abstract:
Potential signatures of proto-planets embedded in their natal protoplanetary disk are radial gaps or cavities in the continuum emission in the IR-mm wavelength range. ALMA observations are now probing spatially resolved rotational line emission of CO and other chemical species. These observations can provide complementary information on the mechanism carving the gaps in dust and additional constraints on the purported planet mass. We post-process 2D hydrodynamical simulations of planet-disk models, where the dust densities and grain size distributions are computed with a dust evolution code. The simulations explore different planet masses (1MJ≤Mp≤15MJ) and turbulent parameters. The outputs are post-processed with the thermo-chemical code DALI, accounting for the radially and vertically varying dust properties as in Facchini et al. (2017). We obtain the gas and dust temperature structures, chemical abundances, and synthetic emission maps of both thermal continuum and CO rotational lines. This is the first study combining hydro simulations, dust evolution and chemistry to predict gas emission of disks hosting massive planets. All radial intensity profiles of the CO main isotopologues show a gap at the planet location. The ratio between the location of the gap as seen in CO and the peak in the mm continuum at the pressure maximum outside the orbit of the planet shows a clear dependence on planet mass. Due to the low dust density in the gaps, the dust and gas components can become thermally decoupled, with the gas being colder than the dust. The gaps seen in CO are due to a combination of gas temperature dropping at the location of the planet, and of the underlying surface density profile. In none of the models is a CO cavity observed, only CO gaps, indicating that one single massive planet is not able to explain the CO cavities observed in transition disks.

On the cavity of a debris disc carved by a giant planet

On the cavity of a debris disc carved by a giant planet 

Authors: 

Regály et al 

Abstract: 

One possible explanation of the cavity in debris discs is the gravitational perturbation of an embedded giant planet. Planetesimals passing close to a massive body are dynamically stirred resulting in a cleared region known as the chaotic zone. Theory of overlapping mean-motion resonances predicts the width of this cavity. To test whether this cavity is identical to the chaotic zone, we investigate the formation of cavities by means of collisionless N-body simulations assuming a 1.25 − 10 Jupiter mass planet with eccentricities of 0 − 0.9. Synthetic images at millimetre wavelengths are calculated to determine the cavity properties by fitting an ellipse to 14 percent contour level. Depending on the planetary eccentricity, epl, the elliptic cavity wall rotates as the planet orbits with the same (epl less than 0.2) or half (epl greater than 0.2) period that of the planet. The cavity centre is offset from the star along the semi-major axis of the planet with a distance of d=0.1q−0.17e0.5pl d=0.1q−0.17epl0.5 in units of cavity size towards the planet’s orbital apocentre, where q is the planet-to-star mass ratio. Pericentre (apocentre) glow develops for epl < 0.05 (epl > 0.1), while both are present for 0.05 ≤ epl ≤ 0.1. Empirical formulae are derived for the sizes of the cavities: δacav = 2.35q0.36 and δacav=7.87q0.37e0.38pl δacav=7.87q0.37epl0.38 for epl ≤ 0.05 and epl greater than 0.05, respectively. The cavity eccentricity, ecav, equals to that of the planet only for 0.3 ≤ epl ≤ 0.6. A new method based on ALMA observations for estimating the orbital parameters and mass of the planet carving the cavity is also given.

TW Hydrae is Forming a SubSaturn Gas Giant

Deep imaging search for planets forming in the TW Hya protoplanetary disk with the Keck/NIRC2 vortex coronagraph


Authors:

Ruane et al

Abstract:
Distinct gap features in the nearest protoplanetary disk, TW Hya (distance of 59.5±0.9 pc), may be signposts of ongoing planet formation. We performed long-exposure thermal infrared coronagraphic imaging observations to search for accreting planets especially within dust gaps previously detected in scattered light and submm-wave thermal emission. Three nights of observations with the Keck/NIRC2 vortex coronagraph in L′ (3.4-4.1μm) did not reveal any statistically significant point sources. We thereby set strict upper limits on the masses of non-accreting planets. In the four most prominent disk gaps at 24, 41, 47, and 88 au, we obtain upper mass limits of 1.6-2.3, 1.1-1.6, 1.1-1.5, and 1.0-1.2 Jupiter masses (MJ) assuming an age range of 7-10 Myr for TW Hya. These limits correspond to the contrast at 95\% completeness (true positive fraction of 0.95) with a 1\% chance of a false positive within 1′′ of the star. We also approximate an upper limit on the product of planet mass and planetary accretion rate of MpM˙≲10−8M2J/yr implying that any putative ∼0.1MJ planet, which could be responsible for opening the 24 au gap, is presently accreting at rates insufficient to build up a Jupiter mass within TW Hya's pre-main sequence lifetime.

On the formation of multiple concentric rings and gaps in protoplanetary disks

On the formation of multiple concentric rings and gaps in protoplanetary disks

Authors:

Bae et al

Abstract:

As spiral waves driven by a planet in a gaseous disk steepen into a shock, they deposit angular momentum, opening a gap in the disk. This has been well studied using both linear theory and numerical simulations, but so far, only for the primary spiral arm -- the one directly attached to the planet. Using two-dimensional hydrodynamic simulations, we show that the secondary and tertiary arms driven by a planet can also open gaps as they steepen into shocks. The depths of the secondary/tertiary gaps in surface density grow with time in a low viscosity disk (α=5×10−5), so even low-mass planets (e.g., super-Earth or mini-Neptune) embedded in the disk can open multiple observable gaps, provided that sufficient time has passed. Applying our results to the HL Tau disk, we show that a single 30 Earth-mass planet embedded in the ring at 68.8 au (B5) can reasonably well reproduce the positions of the two major gaps at 13.2 and 32.3 au (D1 and D2), and roughly reproduce two other major gaps at 64.2 and 74.7 au (D5 and D6) seen in the mm continuum. The positions of secondary/tertiary gaps are found to be sensitive to the planetary mass and the disk temperature profile, so with accurate observational measurements on the temperature structure we can use the positions of multiple gaps to constrain the mass of the planet. We also comment on the gaps seen in the TW Hya and HD 163296 disk.

GAPS IN PROTOPLANETARY DISKS AS SIGNATURES OF PLANETS. III. POLARIZATION

GAPS IN PROTOPLANETARY DISKS AS SIGNATURES OF PLANETS. III. POLARIZATION

Author:

Jang-Condell

Abstract:

Polarimetric observations of T Tauri and Herbig Ae/Be stars are a powerful way to image protoplanetary disks. However, interpretation of these images is difficult because the degree of polarization is highly sensitive to the angle of scattering of stellar light off the disk surface. We examine how disks with and without gaps created by planets appear in scattered polarized light as a function of inclination angle. Isophotes of inclined disks without gaps are distorted in polarized light, giving the appearance that the disks are more eccentric or more highly inclined than they truly are. Apparent gap locations are unaffected by polarization, but the gap contrast changes. In face-on disks with gaps, we find that the brightened far edge of the gap scatters less polarized light than the rest of the disk, resulting in slightly decreased contrast between the gap trough and the brightened far edge. In inclined disks, gaps can take on the appearance of being localized "holes" in brightness rather than full axisymmetric structures. Photocenter offsets along the minor axis of the disk in both total intensity and polarized intensity images can be readily explained by the finite thickness of the disk. Alone, polarized scattered light images of disks do not necessarily reveal intrinsic disk structure. However, when combined with total intensity images, the orientation of the disk can be deduced and much can be learned about disk structure and dust properties.

Multiple Disk Gaps and Rings Generated by a Single Super-Earth

Multiple Disk Gaps and Rings Generated by a Single Super-Earth
Authors:

Dong et al

Abstract:
We investigate the observational signatures of super-Earths (i.e., Earth-to-Neptune mass planets) in their natal disks of gas and dust. Combining two-fluid global hydrodynamics simulations with a radiative transfer code, we calculate the distributions of gas and of sub-mm-sized dust in a disk perturbed by a super-Earth, synthesizing images in near-infrared scattered light and the mm-wave thermal continuum for direct comparison with observations. In low viscosity gas (α≲10−4), a super-Earth opens two annular gaps to either side of its orbit by the action of Lindblad torques. This double gap and its associated gas pressure gradients cause dust particles to be dragged by gas into three rings: one ring sandwiched between the two gaps, and two rings located at the gap edges farthest from the planet. Depending on system parameters, additional rings may manifest for a single planet. A double gap located at tens of AUs from a host star in Taurus can be detected in the dust continuum by the Atacama Large Millimeter Array (ALMA) at an angular resolution of ~0".03 after two hours of integration. Ring and gap features persist in a variety of background disk profiles, last for thousands of orbits, and change their relative positions and dimensions depending on the speed and direction of planet migration. Candidate double gaps have been observed by ALMA in systems like HL Tau (D5 and D6) and TW Hya (at 37 and 43 AU); we submit that each double gap is carved by one super-Earth in nearly inviscid gas.

HOW BRIGHT ARE THE GAPS IN CIRCUMBINARY DISK SYSTEMS?

HOW BRIGHT ARE THE GAPS IN CIRCUMBINARY DISK SYSTEMS?

Authors:

Shi et al

Abstract:

When a circumbinary disk surrounds a binary whose secondary's mass is at least $\sim {10}^{-2}\times $ the primary's mass, a nearly empty cavity with radius a few times the binary separation is carved out of the disk. Narrow streams of material pass from the inner edge of the circumbinary disk into the domain of the binary itself, where they eventually join onto the small disks orbiting the members of the binary. Using data from three-dimensional magnetohydrodynamics simulations of this process, we determine the luminosity of these streams; it is mostly due to weak laminar shocks, and is in general only a few percent of the luminosity of adjacent regions of either the circumbinary disk or the "mini-disks." This luminosity therefore hardly affects the deficit in the thermal continuum predicted on the basis of a perfectly dark gap region.

Slowly-growing gap-opening planets trigger weaker vortices

Slowly-growing gap-opening planets trigger weaker vortices

Authors:

Hammer et al

Abstract:

The presence of a giant planet in a low-viscosity disc can create a gap edge in the disc's radial density profile sharp enough to excite the Rossby Wave Instability. This instability may evolve into dust-trapping vortices that might explain the "banana-shaped" features in recently observed asymmetric transition discs with inner cavities. Previous hydrodynamical simulations of planet-induced vortices have neglected the timescale of hundreds to thousands of orbits to grow a massive planet to Jupiter-size. In this work, we study the effect of a giant planet's runaway growth timescale on the lifetime and characteristics of the resulting vortex. For two different planet masses (1 and 5 Jupiter masses) and two different disc viscosities (α=3×10−4 and 3×10−5), we compare the vortices induced by planets with several different growth timescales between 10 and 4000 planet orbits. In general, we find that slowly-growing planets create significantly weaker vortices with lifetimes and surface densities reduced by more than 50%. For the higher disc viscosity, the longest growth timescales in our study inhibit vortex formation altogether. Additionally, slowly-growing planets produce vortices that are up to twice as elongated, with azimuthal extents well above 180∘ in some cases. These unique, elongated vortices likely create a distinct signature in the dust observations that differentiates them from the more concentrated vortices that correspond to planets with faster growth timescales. We find that the low viscosities necessary for vortex formation likely prevent planets from growing quickly enough to trigger the instability in self-consistent models.

Can dead zones create transition disk like structures?

Can dead zones create transition disk like structures?

Authors:

Pinilla et al

Abstract:

Regions of low ionisation where the activity of the magneto-rotational instability is suppressed, the so called dead zones, have been suggested to explain gaps and asymmetries of transition disks. We investigate the gas and dust evolution simultaneously assuming simplified prescriptions for a dead zone and a magnetohydrodynamic (MHD) wind acting on the disk. We explore whether or not the resulting gas and dust distribution can create signatures similar to the ones observed in transition disks. For the dust evolution, we include the transport, growth, and fragmentation of dust particles. To compare with observations, we produce synthetic images in scattered optical light and in thermal emission at mm wavelengths. In all models with a dead zone, a bump in the gas surface density is produced, which is able to efficiently trap large particles (≳1 mm) at the outer edge of the dead zone. The gas bump reaches an amplitude of a factor of ∼5, which can be enhanced by the presence of a MHD wind that removes mass from the inner disk. While our 1D simulations suggest that such a structure can be present only for ∼1 Myr, the structure may be maintained for a longer time when a more realistic 2D/3D simulations are performed. In the synthetic images, gap-like low emission regions are seen at scattered light and in thermal emission at mm wavelengths, as previously predicted in the case of planet-disk interaction. As a conclusion, main signatures of transition disks can be reproduced by assuming a dead zone in the disk, including gap-like structure in scattered light and millimetre continuum emission, and a lower gas surface density within the dead zone. Previous studies showed that the Rossby wave instability can also develop at the edge of such dead zones, forming vortices and creating also asymmetries.

Resolving the planet-hosting inner regions of the LkCa 15 disk

Resolving the planet-hosting inner regions of the LkCa 15 disk

Authors:

Thalmann et al

Abstract:

LkCa 15 hosts a pre-transitional disk as well as at least one accreting protoplanet orbiting in its gap. Previous disk observations have focused mainly on the outer disk, which is cleared inward of ~50 au. The planet candidates, on the other hand, reside at orbital radii around 15 au, where disk observations have been unreliable until recently. Here we present new J-band imaging polarimetry of LkCa 15 with SPHERE IRDIS, yielding the most accurate and detailed scattered-light images of the disk to date down to the planet-hosting inner regions. We find what appear to be persistent asymmetric structures in the scattering material at the location of the planet candidates, which could be responsible at least for parts of the signals measured with sparse-aperture masking. These images further allow us to trace the gap edge in scattered light at all position angles and search the inner and outer disks for morphological substructure. The outer disk appears smooth with slight azimuthal variations in polarized surface brightness, which may be due to shadowing from the inner disk or a two-peaked polarized phase function. We find that the near-side gap edge revealed by polarimetry matches the sharp crescent seen in previous ADI imaging very well. Finally, the ratio of polarized disk to stellar flux is more than six times larger in J-band than in the RI bands.

Smaller Exoplanets Suspected in HD 97048's Gapped Disk?

Direct detection of scattered light gaps in the transitional disk around HD 97048 with VLT/SPHERE

Authors:

Ginski et al

Abstract:

We studied the well known circumstellar disk around the Herbig Ae/Be star HD 97048 with high angular resolution to reveal undetected structures in the disk, which may be indicative of disk evolutionary processes such as planet formation. We used the IRDIS near-IR subsystem of the extreme adaptive optics imager SPHERE at the ESO/VLT to study the scattered light from the circumstellar disk via high resolution polarimetry and angular differential imaging. We imaged the disk in unprecedented detail and revealed four ring-like brightness enhancements and corresponding gaps in the scattered light from the disk surface with radii between 39 au and 341 au. We derived the inclination and position angle as well as the height of the scattering surface of the disk from our observational data. We found that the surface height profile can be described by a single power law up to a separation ~270 au. Using the surface height profile we measured the scattering phase function of the disk and found that it is well consistent with theoretical models of compact dust aggregates. We discuss the origin of the detected features and find that low mass (< 1 M_Jup) nascent planets are a possible explanation.

A Gas Giant Appears to be Lurking the HD 97048's Gapped Disk

A cavity and further radial substructures in the disk around HD~97048

Authors:

van der Plas et al

Abstract:

Context:

Gaps, cavities and rings in circumstellar disks are signposts of disk evolution and planet-disk interactions. We follow the recent suggestion that Herbig Ae/Be disks with a flared disk harbour a cavity, and investigate the disk around HD~97048.

Aims:

We aim to resolve the 34± 4 au central cavity predicted by Maaskant et al. (2013) and to investigate the structure of the disk.

Methods:

We image the disk around HD~97048 using ALMA at 0.85~mm and 2.94~mm, and ATCA (multiple frequencies) observations. Our observations also include the 12CO J=1-0, 12CO J=3-2 and HCO+ J=4-3 emission lines.

Results:

A central cavity in the disk around HD~97048 is resolved with a 40-46 au radius. Additional radial structure present in the surface brightness profile can be accounted for either by an opacity gap at ~90 au or by an extra emitting ring at ~150 au. The continuum emission tracing the dust in the disk is detected out to 355 au. The 12CO J=3-2 disk is detected 2.4 times farther out. The 12CO emission can be traced down to ≈ 10 au scales. Non-Keplerian kinematics are detected inside the cavity via the HCO+ J=4-3 velocity map. The mm spectral index measured from ATCA observations suggests that grain growth has occurred in the HD~97048 disk. Finally, we resolve a highly inclined disk out to 150 au around the nearby 0.5~M⊙ binary ISO-ChaI 126.

Conclusions:

The data presented here reveal a cavity in the disk of HD 97048, and prominent radial structure in the surface brightness. The cavity size varies for different continuum frequencies and gas tracers. The gas inside the cavity follows non-Keplerian kinematics seen in HCO+ emission. The variable cavity size along with the kinematical signature suggests the presence of a substellar companion or massive planet inside the cavity.

A Photo-evaporative gap Observed in the TW Hydrae

A photo-evaporative gap in the closest planet forming disc

Authors:

Ercolano et al

Abstract:

The dispersal of the circumstellar discs of dust and gas surrounding young low- mass stars has important implications for the formation of planetary systems. Photo- evaporation from energetic radiation from the central object is thought to drive the dispersal in the majority of discs, by creating a gap which disconnects the outer from the inner regions of the disc and then disperses the outer disc from the inside-out, while the inner disc keeps draining viscously onto the star. In this Letter we show that the disc around TW Hya, the closest protoplanetary disc to Earth, may be the first object where a photoevaporative gap has been imaged around the time at which it is being created. Indeed the detected gap in the ALMA images is consistent with the expectations of X-ray photoevaporation models, thus not requiring the presence of a planet. The photoevaporation model is also consistent with a broad range of properties of the TW Hya system, e.g. accretion rate and the location of the gap at the onset of dispersal. We show that the central, unresolved 870 {\mu}m continuum source might be produced by free free emission from the gas and/or residual dust inside the gap.

Gap Formation in Gas Giant Formation in a Photoevaporating Protoplanetary Disk

GAS GIANT PLANET FORMATION IN THE PHOTOEVAPORATING DISK. I. GAP FORMATION

Authors:

Xiao et al

Abstract:

Planet formation and photoevaporation have both been considered as gap opening mechanisms in protoplanetary disks. We have studied giant planet formation in a photoevaporating disk with long-term evolution. Our calculations suggest that the core accretion rate of a protoplanet declines and the trigger of the runaway gas accretion for a giant planet is delayed under the action of photoevaporation. We find that the final mass of a giant planet characterized by the "gap-limiting" case is not influenced by photoevaporation but the final mass of a giant planet characterized by the "diffusion-limiting" case is greatly influenced by photoevaporation. Considering the formation process of giant planets, we suggest that the locations of the gaps opened by giant planets are within 30–40 au and the gap width in the "gap-limiting" case is wider than that in the "diffusion-limiting" case. We also find that gaps in photoevaporating disks are wider than those in non-photoevaporating disks. Our calculations suggest that the origins of multiple gaps in a disk can be diverse depending on their formation locations. In the formation region of giant planets, gaps are opened by giant planets. The outer gap beyond the giant planet formation region may be opened under the action of photoevaporation. A gap may also be opened at 1–3 au under the actions of photoevaporating dissipation and gas accretion of the outer giant planets.

STABILITY AND OCCURRENCE RATE CONSTRAINTS ON THE PLANETARY SCULPTING HYPOTHESIS FOR "TRANSITIONAL" DISKS

STABILITY AND OCCURRENCE RATE CONSTRAINTS ON THE PLANETARY SCULPTING HYPOTHESIS FOR "TRANSITIONAL" DISKS

Authors:

Dong et al

Abstract:

Transitional disks, protoplanetary disks with deep and wide central gaps, may be the result of planetary sculpting. By comparing numerical planet-opening-gap models with observed gaps, we find systems of 3–6 giant planets are needed in order to open gaps with the observed depths and widths. We explore the dynamical stability of such multi-planet systems using N-body simulations that incorporate prescriptions for gas effects. We find they can be stable over a typical disk lifetime, with the help of eccentricity damping from the residual gap gas that facilitates planets locking into mean motion resonances. However, in order to account for the occurrence rate of transitional disks, the planet sculpting scenario demands gap-opening-friendly disk conditions, in particular, a disk viscosity α lesssim 0.001. In addition, the demography of giant planets at ~3–30 au separations, poorly constrained by current data, has to largely follow occurrence rates extrapolated outward from radial velocity surveys, not the lower occurrence rates extrapolated inward from direct imaging surveys. Even with the most optimistic occurrence rates, transitional disks cannot be a common phase that most gas disks experience at the end of their life, as popularly assumed, simply because there are not enough planets to open these gaps. Finally, as consequences of demanding almost all giant planets at large separations participate in transitional disk sculpting, the majority of such planets must form early and end up in a chain of mean motion resonances at the end of disk lifetime.

2MASS J16042165-2130284 Probably has a Brown Dwarf & Several Gas Giants

Constraining the mass of the planet(s) sculpting a disk cavity

Authors:

Wilson Canovas et al

Abstract:

2MASS J16042165-2130284 (hereafter J1604) is a pre-transitional disk with different gap sizes in the mm-sized (~79 au) and μm-sized (~63 au) dust particles. The 12CO emission shows a ~30 au cavity. This radial structure suggests that giant planets are interacting with the disk.

We aim to observationally constrain the masses and location of plausible giant planets inside the cavity of J1604, and compare our results with previous predictions from hydrodynamical models describing planet-disk interactions.

We observed J1604 with VLT/SPHERE in pupil-stabilized mode, obtaining YJHK- band images. The dataset was processed exploiting the ADI technique with dedicated algorithms to maximize the sensitivity of our observations.

Our observations reach an exquisite contrast of ΔK,H 12 mag from 0.15" to 0.80" ( 22 to 115 au), but no planet candidate is detected. The disk is directly imaged in scattered light in all the near infrared bands (from Y to K). The disk has a red color, which indicates that the dust particles in the disk surface are mainly ≳0.3μm-sized grains. We confirm the sharp dip/decrement in scattered light in agreement with previous observations. Comparing our images with a simple radiative transfer model we argue that the nearest side of the disk is most likely the southern side.

Our observations represent a gain of roughly ΔK=6 in contrast when compared to previous observations of this object. The work detailed here represents the deepest search yet for companions of J1604 which are potentially carving its disk structure. We reach a mass sensitivity of 2−3MJup across the disk cavity according to a hot start scenario. We propose that a brown dwarf orbiting inside the inner ~15 au and additional Jovian planets at larger radii could account for the observed properties of J1604 while explaining our non-detection.

Discovery of concentric broken rings at sub-arcsec separations in the HD 141569A gas-rich, debris disk with VLT/SPHERE

Discovery of concentric broken rings at sub-arcsec separations in the HD 141569A gas-rich, debris disk with VLT/SPHERE

Authors:

Perrot et al

Abstract:

Transition disks correspond to a short stage between the young protoplanetary phase and older debris phase. Along this evolutionary sequence, the gas component disappears leaving room for a dust-dominated environment where already-formed planets signpost their gravitational perturbations. We endeavor to study the very inner region of the well-known and complex debris, but still gas-rich disk, around HD 141569A using the exquisite high-contrast capability of SPHERE at the VLT. Recent near-infrared (IR) images suggest a relatively depleted cavity within ~200 au, while former mid-IR data indicate the presence of dust at separations shorter than ~100 au. We obtained multi-wavelength images in the near-IR in J, H2, H3 and Ks bands with the IRDIS camera and a 0.95-1.35 micrometers spectral data cube with the IFS. Data were acquired in pupil-tracking mode, thus allowing for angular differential imaging. We discovered several new structures inside 1", of which the most prominent is a bright ring with sharp edges (semi-major axis: 0.4") featuring a strong north-south brightness asymmetry. Other faint structures are also detected from 0.4" to 1" in the form of concentric ringlets and at least one spiral arm. Finally, the VISIR data at 8.6 micrometers suggests the presence of an additional dust population closer in. Besides, we do not detect companions more massive than 1-3 mass of Jupiter. The performance of SPHERE allows us to resolve the extended dust component, which was previously detected at thermal and visible wavelengths, into very complex patterns with strong asymmetries ; the nature of these asymmetries remains to be understood. Scenarios involving shepherding by planets or dust-gas interactions will have to be tested against these observations.

Multiple gaps with large grain deficit in the protoplanetary disk around TW Hya

Multiple gaps with large grain deficit in the protoplanetary disk around TW Hya

Authors:

Tsukagoshi et al

Abstract:

We report ∼3 au resolution imaging observations of the protoplanetary disk around TW Hya at 138 and 230 GHz with the Atacama Large Millimeter/Submillimeter Array. Our observations revealed two deep gaps (∼25--50 %) at 22 and 37 au and shallower gaps (a few %) at 6, 28, and 44 au, as recently reported by Andrews et al. (2016). The central hole with a radius of ∼3 au was also marginally resolved. The most remarkable finding is that the power-law index of the dust opacity β, derived from the spectral index α between bands 4 and 6, peaks at the 22 au gap with β∼1.7 and decreases toward the disk center to β∼0. Our model fitting suggests that the overall disk structure can be reproduced with the inner hole and the gaps at 22 and 37 au. The most prominent gap at 22~au could be caused by the gravitational interaction between the disk and an unseen planet with a mass of ≲1.5 MNeptune although other origins may be possible. The planet-induced gap is supported by the fact that β is enhanced at the 22 au gap, indicating a deficit of ∼mm-sized grains within the gap due to dust filtration by a planet. Alternatively, the destruction of large dust aggregates due to the sintering of major volatiles might cause the multiple ring structure. We also find weak sinusoidal patterns with wavelengths of 5--10 au, which may be related to dynamical instabilities within the disk.