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.

ALMA 1.3 Millimeter Map of the HD 95086 System

ALMA 1.3 Millimeter Map of the HD 95086 System

Authors:

Su et al

Abstract:

Planets and minor bodies such as asteroids, Kuiper-belt objects and comets are integral components of a planetary system. Interactions among them leave clues about the formation process of a planetary system. The signature of such interactions is most prominent through observations of its debris disk at millimeter wavelengths where emission is dominated by the population of large grains that stay close to their parent bodies. Here we present ALMA 1.3 mm observations of HD 95086, a young early-type star that hosts a directly imaged giant planet b and a massive debris disk with both asteroid- and Kuiper-belt analogs. The location of the Kuiper-belt analog is resolved for the first time. The system can be depicted as a broad (ΔR/R∼0.84), inclined (30\arcdeg±3\arcdeg) ring with millimeter emission peaked at 200±6 au from the star. The 1.3 mm disk emission is consistent with a broad disk with sharp boundaries from 106±6 to 320±20 au with a surface density distribution described by a power law with an index of --0.5±0.2. Our deep ALMA map also reveals a bright source located near the edge of the ring, whose brightness at 1.3 mm and potential spectral energy distribution are consistent with it being a luminous star-forming galaxy at high redshift. We set constraints on the orbital properties of planet b assuming co-planarity with the observed disk.

Dynamical models to explain observations with SPHERE in planetary systems with double debris belts

Dynamical models to explain observations with SPHERE in planetary systems with double debris belts

Authors:
Lazzoni et al

Abstract:
A large number of systems harboring a debris disk show evidence for a double belt architecture. One hypothesis for explaining the gap between the belts is the presence of one or more planets dynamically carving it. This work aims to investigate this scenario in systems harboring two components debris disks. All the targets in the sample were observed with the SPHERE instrument which performs high-contrast direct imaging. Positions of the inner and outer belts were estimated by SED fitting of the infrared excesses or, when available, from resolved images of the disk. Very few planets have been observed so far in debris disks gaps and we intended to test if such non-detections depend on the observational limits of the present instruments. This aim is achieved by deriving theoretical predictions of masses, eccentricities and semi-major axes of planets able to open the observed gaps and comparing such parameters with detection limits obtained with SPHERE. The relation between the gap and the planet is due to the chaotic zone around the orbit of the planet. The radial extent of this zone depends on the mass ratio between the planet and the star, on the semi-major axis and on the eccentricity of the planet and it can be estimated analytically. We apply the formalism to the case of one planet on a circular or eccentric orbit. We then consider multi-planetary systems: 2 and 3 equal-mass planets on circular orbits and 2 equal-mass planets on eccentric orbits in a packed configuration. We then compare each couple of values (M,a), derived from the dynamical analysis of single and multiple planetary models, with the detection limits obtained with SPHERE. Our results show that the apparent lack of planets in gaps between double belts could be explained by the presence of a system of two or more planets possibly of low mass and on an eccentric orbits whose sizes are below the present detection limits.

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.

Stellar Winds and Dust Avalanches in the AU Mic Debris Disk

Stellar Winds and Dust Avalanches in the AU Mic Debris Disk

Authors: 

Chiang et al 

Abstract:
We explain the fast-moving, ripple-like features in the edge-on debris disk orbiting the young M dwarf AU Mic. The bright features are clouds of submicron dust repelled by the host star's wind. The clouds are produced by avalanches: radial outflows of dust that gain exponentially more mass as they shatter background disk particles in collisional chain reactions. The avalanches are triggered from a region a few au across—the "avalanche zone"—located on AU Mic's primary "birth" ring at a true distance of ~35 au from the star but at a projected distance more than a factor of 10 smaller: the avalanche zone sits directly along the line of sight to the star, on the side of the ring nearest Earth, launching clouds that disk rotation sends wholly to the southeast, as observed. The avalanche zone marks where the primary ring intersects a secondary ring of debris left by the catastrophic disruption of a progenitor up to Varuna in size, less than tens of thousands of years ago. Only where the rings intersect are particle collisions sufficiently violent to spawn the submicron dust needed to seed the avalanches. We show that this picture works quantitatively, reproducing the masses, sizes, and velocities of the observed escaping clouds. The Lorentz force exerted by the wind's magnetic field, whose polarity reverses periodically according to the stellar magnetic cycle, promises to explain the observed vertical undulations. The timescale between avalanches, about 10 yr, might be set by time variability of the wind mass loss rate or, more speculatively, by some self-regulating limit cycle.

An Incipient Debris Disk in the Chamaeleon I Cloud

An Incipient Debris Disk in the Chamaeleon I Cloud

Authors:

Espaillat et al

Abstract:
The point at which a protoplanetary disk becomes a debris disk is difficult to identify. To better understand this, here we study the ∼40~AU separation binary T~54 in the Chamaeleon I cloud. We derive a K5 spectral type for T~54~A (which dominates the emission of the system) and an age of ∼2~Myr. However, the dust disk properties of T~54 are consistent with those of debris disks seen around older and earlier-type stars. At the same time, T~54 has evidence of gas remaining in the disk as indicated by [Ne II], [Ne III], and [O I] line detections. We model the spectral energy distribution of T~54 and estimate that ∼3×10−3 Earth-masses of small dust grains (<0 .25="" along="" an="" are="" at="" circumbinary="" disk="" earth-masses="" in="" larger="" least="" m="" of="" optically="" present="" thin="" with="">10~μm) grains within a circumprimary disk. Assuming a solar-like mixture, we use Ne line luminosities to place a minimum limit on the gas mass of the disk (∼3×10−4 Earth-masses) and derive a gas-to-dust mass ratio of ∼0.1. We do not detect substantial accretion, but we do see Hα in emission in one epoch, suggestive that there may be intermittent dumping of small amounts of matter onto the star. Considering the low dust mass, the presence of gas, and young age of T~54, we conclude that this system is on the bridge between the protoplanetary and debris disk stages.

Giant Planets Can Act As Stabilizing Agents on Debris Disks

Giant Planets Can Act As Stabilizing Agents on Debris Disks

Authors:

Muñoz-Gutiérrez et al

Abstract:
We have explored the evolution of a cold debris disk under the gravitational influence of dwarf planet sized objects (DPs), both in the presence and absence of an interior giant planet. Through detailed long-term numerical simulations, we demonstrate that, when the giant planet is not present, DPs can stir the eccentricities and inclinations of disk particles, in linear proportion to the total mass of the DPs; on the other hand, when the giant planet is included in the simulations, the stirring is approximately proportional to the mass squared. This creates two regimes: below a disk mass threshold (defined by the total mass of DPs), the giant planet acts as a stabilizing agent of the orbits of cometary nucleii, diminishing the effect of the scatterers; above the threshold, the giant contributes to the dispersion of the particles.

A Complete ALMA Map of the Fomalhaut Debris Disk

A Complete ALMA Map of the Fomalhaut Debris Disk

Authors:

MacGregor et al

Abstract:

We present ALMA mosaic observations at 1.3 mm (223 GHz) of the Fomalhaut system with a sensitivity of 14 μJy/beam. These observations provide the first millimeter map of the continuum dust emission from the complete outer debris disk with uniform sensitivity, enabling the first conclusive detection of apocenter glow. We adopt a MCMC modeling approach that accounts for the eccentric orbital parameters of a collection of particles within the disk. The outer belt is radially confined with an inner edge of 136.3±0.9 AU and width of 13.5±1.8 AU. We determine a best-fit eccentricity of 0.12±0.01. Assuming a size distribution power law index of q=3.46±0.09, we constrain the dust absorptivity power law index β to be 0.9<β<1.5. The geometry of the disk is robustly constrained with inclination 65.∘6±0.∘3, position angle 337.∘9±0.∘3, and argument of periastron 22.∘5±4.∘3. Our observations do not confirm any of the azimuthal features found in previous imaging studies of the disk with HST, SCUBA, and ALMA. However, we cannot rule out structures ≤10AU in size or which only affect smaller grains. The central star is clearly detected with a flux density of 0.75±0.02 mJy, significantly lower than predicted by current photospheric models. We discuss the implications of these observations for the directly imaged Fomalhaut b and the inner dust belt detected at infrared wavelengths.

ALMA Detects Debris Disk Around Fomalhaut

An international team of astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) has made the first complete millimeter-wavelength image of the ring of dusty debris surrounding the young star Fomalhaut. This remarkably well-defined band of rubble and gas is likely the result of exocomets smashing together near the outer edges of a planetary system 25 light-years from Earth.

Earlier ALMA observations of Fomalhaut -- taken in 2012 when the telescope was still under construction - revealed only about one half of the debris disk. Though this first image was merely a test of ALMA's initial capabilities, it nonetheless provided tantalizing hints about the nature and possible origin of the disk.

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First resolved image of the HD 114082 debris disk in the Lower Centaurus Crux with SPHERE

The SHARDDS survey: First resolved image of the HD 114082 debris disk in the Lower Centaurus Crux with SPHERE

Authors:

Wahhaj et al

Abstract:

We present the first resolved image of the debris disk around the 16 ± 8 Myr old star, HD 114082. The observation was made in the H-band using the SPHERE instrument. The star is at a distance of 92 ± 6 pc in the Lower Centaurus Crux association. Using a Markov chain Monte Carlo analysis, we determined that the debris is likely in the form of a dust ring with an inner edge of 27.7+2.8-3.5 au, position angle –74.3°+0.5-1.5, and an inclination with respect to the line of sight of 6.7°+3.8-0.4. The disk imaged in scattered light has a surface density that is declining with radius of ~r-4, which is steeper than expected for grain blowout by radiation pressure. We find only marginal evidence (2σ) of eccentricity and rule out planets more massive than 1.0 MJup orbiting within 1 au of the inner edge of the ring, since such a planet would have disrupted the disk. The disk has roughly the same fractional disk luminosity (Ldisk/L∗ = 3.3 × 10-3) as HR 4796 A and β Pictoris, however it was not detected by previous instrument facilities most likely because of its small angular size (radius ~0.4′′), low albedo (~0.2), and low scattering efficiency far from the star due to high scattering anisotropy. With the arrival of extreme adaptive optics systems, such as SPHERE and GPI, the morphology of smaller, fainter, and more distant debris disks are being revealed, providing clues to planet-disk interactions in young protoplanetary systems.

A WISE-based search for debris discs amongst M-dwarfs in nearby, young, moving groups

A WISE-based search for debris discs amongst M-dwarfs in nearby, young, moving groups

Authors:

Binks et al

Abstract:

We present a search for debris discs amongst M-dwarf members of nearby, young (5-150 Myr) moving groups (MGs) using infrared (IR) photometry, primarily from the Wide Infrared Survey Explorer (WISE). A catalogue of 100 MG M-dwarfs that have suitable WISE data is compiled and 19 of these are found to have significant IR excess emission at 22μm. Our search is likely to be complete for discs where the ratio of flux from the disc to flux from the star fd/f∗>10−3. The spectral energy distributions are supplemented with 2MASS photometry and data at longer wavelengths and fitted with simple disc models to characterise the IR excesses. There is a bimodal distribution -- twelve targets have W1−W4>3, corresponding to fd/f∗>0.02 and are likely to be gas-rich, primordial discs. The remaining seven targets have W1−W4<1 (fd/f∗≲10−3) and include three objects with previously known or suspected debris discs and four new debris disc candidates that are all members of the Beta Pic MG. All of the IR excesses are identified in stars that are likely members of MGs with age <30 Myr. The detected debris disc frequency falls from 13 to 5 per cent to <7 per cent (at 95 per cent confidence) for objects younger or older than 30 Myr respectively. This provides evidence for the evolution of debris discs on this timescale and does not support models where the maximum of debris disc emission occurs much later in lower-mass stars.

Are a Chain of Nemesis Class Exoplanets Scattering Comets Inwards in the η Corvi System?

ALMA observations of the η Corvi debris disc: inward scattering of CO-rich exocomets by a chain of 3-30 M⊕ planets?

Authors:

Marino et al

Abstract:

While most of the known debris discs present cold dust at tens of AU, a few young systems exhibit hot dust analogous to the Zodiacal dust. η Corvi is particularly interesting as it is old and it has both, with its hot dust significantly exceeding the maximum luminosity of an in-situ collisional cascade. Previous work suggested that this system could be undergoing an event similar to the Late Heavy Bombardment (LHB) soon after or during a dynamical instability. Here we present ALMA observations of η Corvi with a resolution of 1."2 (~22au) to study its outer belt. The continuum emission is consistent with an axisymmetric belt, with a mean radius of 152au and radial FWHM of 46au, which is too narrow compared to models of inward scattering of an LHB-like scenario. Instead, the hot dust could be explained as material passed inwards in a rather stable planetary configuration. We also report a 4sigma detection of CO at ~ 20au. CO could be released in situ from icy planetesimals being passed in when crossing the H2O or CO2 ice lines. Finally, we place constraints on hidden planets in the disc. If a planet is sculpting the disc's inner edge, this should be orbiting at 75-100au, with a mass of 3-30 M⊕ and an eccentricity < 0.08. Such a planet would be able to clear its chaotic zone on a timescale shorter than the age of the system and scatter material inwards from the outer belt to the inner regions, thus feeding the hot dust.

Explorations of Dusty Debris Disk Geometry

Explorations of Dusty Debris Disk Geometry

Authors:

Dennihy et al

Abstract:

As the sample of white dwarfs with signatures of planetary systems has grown, statistical studies have begun to suggest our picture of compact debris disk formation from disrupted planetary bodies is incomplete. Here we present the results of an effort to extend the preferred dust disk model introduced by \citet{jur03} to include elliptical geometries. We apply this model the observed distribution of fractional infrared luminosities, and explore the difference in preferred parameter spaces for a circular and highly elliptical model on a well-studied dusty white dwarf.

Linking long-term planetary N-body simulations with periodic orbits: application to white dwarf pollution

Linking long-term planetary N-body simulations with periodic orbits: application to white dwarf pollution

Authors:

Antoniadou et al

Abstract:

Mounting discoveries of debris discs orbiting newly-formed stars and white dwarfs (WDs) showcase the importance of modeling the long-term evolution of small bodies in exosystems. WD debris discs are in particular thought to form from very long-term (0.1-5.0 Gyr) instability between planets and asteroids. However, the time-consuming nature of N-body integrators which accurately simulate motion over Gyrs necessitates a judicious choice of initial conditions. The analytical tools known as \textit{periodic orbits} can circumvent the guesswork. Here, we begin a comprehensive analysis directly linking periodic orbits with N-body integration outcomes with an extensive exploration of the planar circular restricted three-body problem (CRTBP) with an outer planet and inner asteroid near or inside of the 2:1 mean motion resonance. We run nearly 1000 focused simulations for the entire age of the Universe (14 Gyr) with initial conditions mapped to the phase space locations surrounding the unstable and stable periodic orbits for that commensurability. In none of our simulations did the planar CRTBP architecture yield a long-timescale (≳0.25% of the age of the Universe) asteroid-star collision. The pericentre distance of asteroids which survived beyond this timescale (≈35 Myr) varied by at most about 60%. These results help affirm that collisions occur too quickly to explain WD pollution in the planar CRTBP 2:1 regime, and highlight the need for further periodic orbit studies with the eccentric and inclined TBP architectures and other significant orbital period commensurabilities.

Mass and eccentricity constraints on the planetary debris orbiting the white dwarf WD 1145+017

Mass and eccentricity constraints on the planetary debris orbiting the white dwarf WD 1145+017

Authors:

Gurri et al

Abstract:

Being the first of its kind, the white dwarf WD 1145+017 exhibits a complex system of disintegrating debris which offers a unique opportunity to study its disruption process in real time. Even with plenty of transit observations there are no clear constraints on the masses or eccentricities of such debris. Using N-body simulations we show that masses greater than approximately 1020 kg (a tenth of the mass of Ceres) or orbits that are not nearly circular (eccentricity>10−3) dramatically increase the chances of the system becoming unstable within two years, which would contrast with the observational data over this timespan. We also provide a direct comparison between transit phase shifts detected in the observations and by our numerical simulations.

Young White Dwarf WD 1536+520 has Solar-like Abudances of Rock Forming Elements

Solar Abundances of Rock Forming Elements, Extreme Oxygen and Hydrogen in a Young Polluted White Dwarf

Authors:

Farihi et al

Abstract:

The Teff = 20,800 K white dwarf WD 1536+520 is shown to have broadly solar abundances of the major rock forming elements O, Mg, Al, Si, Ca, and Fe, together with a strong relative depletion in the volatile elements C and S. In addition to the highest metal abundances observed to date, including log(O/He) = -3.4, the helium-dominated atmosphere has an exceptional hydrogen abundance at log(H/He) = -1.7. Within the uncertainties, the metal-to-metal ratios are consistent with the accretion of an H2O-rich and rocky parent body, an interpretation supported by the anomalously high trace hydrogen. The mixed atmosphere yields unusually short diffusion timescales for a helium atmosphere white dwarf, of no more than a few hundred yr, and equivalent to those in a much cooler, hydrogen-rich star. The overall heavy element abundances of the disrupted parent body deviate modestly from a bulk Earth pattern, and suggest the deposition of some core-like material. The total inferred accretion rate is 4.2e9 g/s, and at least 4 times higher than any white dwarf with a comparable diffusion timescale. Notably, when accretion is exhausted in this system, both metals and hydrogen will become undetectable within roughly 300 Myr, thus supporting a scenario where the trace hydrogen is related to the ongoing accretion of planetary debris.

Planetary systems in star clusters

Planetary systems in star clusters

Authors:

Kouwenhoven et al

Abstract:

Thousands of confirmed and candidate exoplanets have been identified in recent years. Consequently, theoretical research on the formation and dynamical evolution of planetary systems has seen a boost, and the processes of planet-planet scattering, secular evolution, and interaction between planets and gas/debris disks have been well-studied. Almost all of this work has focused on the formation and evolution of isolated planetary systems, and neglect the effect of external influences, such as the gravitational interaction with neighbouring stars. Most stars, however, form in clustered environments that either quickly disperse, or evolve into open clusters. Under these conditions, young planetary systems experience frequent close encounters with other stars, at least during the first 1-10 Myr, which affects planets orbiting at any period range, as well as their debris structures.

DEBRIS DISKS IN THE SCORPIUS–CENTAURUS OB ASSOCIATION RESOLVED BY ALMA

DEBRIS DISKS IN THE SCORPIUS–CENTAURUS OB ASSOCIATION RESOLVED BY ALMA

Authors:

Lieman-Sifry et al

Abstract:

We present a CO(2-1) and 1240 μm continuum survey of 23 debris disks with spectral types B9-G1, observed at an angular resolution of 0farcs5–1'' with the Atacama Large Millimeter/Submillimeter Array (ALMA). The sample was selected for large infrared excess and age ~10 Myr, to characterize the prevalence of molecular gas emission in young debris disks. We identify three CO-rich debris disks, plus two additional tentative (3σ) CO detections. Twenty disks were detected in the continuum at the >3σ level. For the 12 disks in the sample that are spatially resolved by our observations, we perform an independent analysis of the interferometric continuum visibilities to constrain the basic dust disk geometry, as well as a simultaneous analysis of the visibilities and broadband spectral energy distribution to constrain the characteristic grain size and disk mass. The gas-rich debris disks exhibit preferentially larger outer radii in their dust disks, and a higher prevalence of characteristic grain sizes smaller than the blowout size. The gas-rich disks do not exhibit preferentially larger dust masses, contrary to expectations for a scenario in which a higher cometary destruction rate would be expected to result in a larger mass of both CO and dust. The three debris disks in our sample with strong CO detections are all around A stars: the conditions in disks around intermediate-mass stars appear to be the most conducive to the survival or formation of CO.

Faint Warm Debris Disks Around Nearby Bright Stars

Faint warm debris disks around nearby bright stars explored by AKARI and IRSF

Authors:

Ishihara et al

Abstract:

Context:

Debris disks are important observational clues for understanding planetary-system formation process. In particular, faint warm debris disks may be related to late planet formation near 1 AU. A systematic search of faint warm debris disks is necessary to reveal terrestrial planet formation.

Aims:

Faint warm debris disks show excess emission that peaks at mid-IR wavelengths. Thus we explore debris disks using the AKARI mid-IR all-sky point source catalog (PSC), a product of the second generation unbiased IR all-sky survey.

Methods:

We investigate IR excess emission for 678 isolated main-sequence stars for which there are 18 micron detections in the AKARI mid-IR all-sky catalog by comparing their fluxes with the predicted fluxes of the photospheres based on optical to near-IR fluxes and model spectra. The near-IR fluxes are first taken from the 2MASS PSC. However, 286 stars with Ks<4 .5="" 1.4="" 1.8="" 14="" 2mass="" accuracy="" accurate="" africa="" and="" applying="" average.="" band="" br="" density="" due="" errors="" filters="" flux="" fluxes="" for="" from="" h="" have="" imager="" improved="" in="" infrared="" irsf="" j="" ks="" large="" m="" measured="" near-ir="" neutral="" on="" our="" phi="" photometry="" sample="" saturation.="" simultaneous="" south="" survey="" telescope="" the="" thus="" to="" unbiased="" we="">
Results:

We identified 53 debris-disk candidates including eight new detections from our sample of 678 main-sequence stars. The detection rate of debris disks for this work is ~8%, which is comparable with those in previous works by Spitzer and Herschel.

Conclusion:

The importance of this study is the detection of faint warm debris disks around nearby field stars. At least nine objects have a large amount of dust for their ages, which cannot be explained by the conventional steady-state collisional cascade model.