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.

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.

ALMA Observes Exoplanet Formation Around V1247 Orionis

The quest to discover how planets found in the far reaches of the universe are born has taken a new, crucial twist.

A new study by an international team of scientists, led by Stefan Kraus from the University of Exeter, has given a fascinating new insight into one of the most respected theories of how planets are formed.

Young stars start out with a massive disk of gas and dust that over time, astronomers think, either diffuses away or coalesces into planets and asteroids.

However, scientists are still searching for a complete understanding of how these early formations come together to form asteroid-sized objects. One reason has been that drag in the disk produced by surrounding gas makes the grains move inward toward the star - which can in turn deplete the disk rapidly in a process known as "radial drift."

In the new research, the team use high powered telescopes to target the star V1247 Orionis -, a young, hot star surrounded by a dynamic ring of gas and dust.

The team produced a detailed image of the star and its surrounding dust disc, shown in two parts: a clearly defined central ring of matter and a more delicate crescent structure located further out.

The region between the ring and crescent, visible as a dark strip, is thought to be caused by a young planet carving its way through the disc. As the planet moves around in its orbit, its motion creates areas of high pressure on either side of its path, similar to how a ship creates bow waves as it cuts through water.

These areas of high pressure could become protective barriers around sites of planet formation; dust particles are trapped within them for millions of years, allowing them the time and space to clump together and grow.

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ALMA Observations of the Young Substellar Binary System 2M1207

ALMA Observations of the Young Substellar Binary System 2M1207

Authors:

Ricci et al

Abstract:

We present ALMA observations of the 2M1207 system, a young binary made of a brown dwarf with a planetary-mass companion at a projected separation of about 40 au. We detect emission from dust continuum at 0.89 mm and from the $J=3-2$ rotational transition of CO from a very compact disk around the young brown dwarf. The small radius found for this brown dwarf disk may be due to truncation from the tidal interaction with the planetary-mass companion. Under the assumption of optically thin dust emission, we estimate a dust mass of 0.1 M ⊕ for the 2M1207A disk and a 3σ upper limit of ~1 M Moon for dust surrounding 2M1207b, which is the tightest upper limit obtained so far for the mass of dust particles surrounding a young planetary-mass companion. We discuss the impact of this and other non-detections of young planetary-mass companions for models of planet formation that predict circumplanetary material to surround these objects.

An ALMA Survey of CO isotopologue emission from Protoplanetary Disks in Chamaeleon I

An ALMA Survey of CO isotopologue emission from Protoplanetary Disks in Chamaeleon I

Authors:

Long et al

Abstract:

The mass of a protoplanetary disk limits the formation and future growth of any planet. Masses of protoplanetary disks are usually calculated from measurements of the dust continuum emission by assuming an interstellar gas-to-dust ratio. To investigate the utility of CO as an alternate probe of disk mass, we use ALMA to survey 13CO and C18O J = 3−2 line emission from a sample of 93 protoplanetary disks around stars and brown dwarfs with masses from 0.03 -- 2 M⊙ in the nearby Chamaeleon I star-forming region. We detect 13CO emission from 17 sources and C18O from only one source. Gas masses for disks are then estimated by comparing the CO line luminosities to results from published disk models that include CO freeze-out and isotope-selective photodissociation. Under the assumption of a typical ISM CO-to-H2 ratios of 10−4, the resulting gas masses are implausibly low, with an average gas mass of ∼ 0.05 MJup as inferred from the average flux of stacked 13CO lines. The low gas masses and gas-to-dust ratios for Cha I disks are both consistent with similar results from disks in the Lupus star-forming region. The faint CO line emission may instead be explained if disks have much higher gas masses, but freeze-out of CO or complex C-bearing molecules is underestimated in disk models. The conversion of CO flux to CO gas mass also suffers from uncertainties in disk structures, which could affect gas temperatures. CO emission lines will only be a good tracer of the disk mass when models for C and CO depletion are confirmed to be accurate.

1.3-mm ALMA observations of the Fomalhaut debris system

1.3-mm ALMA observations of the Fomalhaut debris system

Authors:

White et al

Abstract:
We present Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 observations (1.3 mm/233 GHz) of Fomalhaut and its debris disc. The observations achieve a sensitivity of 17 μJy and a resolution of 0.28 arcsec (2.1 au at a distance of 7.66 pc), which are the highest resolution observations to date of the millimetre grains in Fomalhaut's main debris ring. The ring is tightly constrained to 139+2−3/139−3+2 au with a full width at half-maximum of 13 ± 3 au, following a Gaussian profile. The millimetre spectral index is constrained to αmm = −2.73 ± 0.13. We explore fitting debris disc models in the image plane, as well as fitting models using visibility data directly. The results are compared and the potential advantages/disadvantages of each approach are discussed. The detected central emission is indistinguishable from a point source, with a most probable flux of 0.90 ± 0.12 mJy (including calibration uncertainties). This implies that any inner debris structure, as was inferred from far-infrared observations, must contribute little to the total central emission. Moreover, the stellar flux is less than 70 per cent of that predicted by extrapolating a blackbody from the constrained stellar photosphere temperature. This result emphasizes that unresolved inner debris components cannot be fully characterized until the behaviour of the host star's intrinsic stellar emission at millimetre wavelengths is properly understood.

The Flying Saucer: Tomography of the thermal and density gas structure of an edge-on protoplanetary disk

The Flying Saucer: Tomography of the thermal and density gas structure of an edge-on protoplanetary disk

Authors:

Dutrey et al

Abstract:
Determining the gas density and temperature structures of protoplanetary disks is a fundamental task to constrain planet formation theories. This is a challenging procedure and most determinations are based on model-dependent assumptions. We attempt a direct determination of the radial and vertical temperature structure of the Flying Saucer disk, thanks to its favorable inclination of 90 degrees. We present a method based on the tomographic study of an edge-on disk. Using ALMA, we observe at 0.5" resolution the Flying Saucer in CO J=2-1 and CS J=5-4. This edge-on disk appears in silhouette against the CO J=2-1 emission from background molecular clouds in ρ Oph. The combination of velocity gradients due to the Keplerian rotation of the disk and intensity variations in the CO background as a function of velocity provide a direct measure of the gas temperature as a function of radius and height above the disk mid-plane. The overall thermal structure is consistent with model predictions, with a cold (less than 15−12 ~K), CO-depleted mid-plane, and a warmer disk atmosphere. However, we find evidence for CO gas along the mid-plane beyond a radius of about 200\,au, coincident with a change of grain properties. Such a behavior is expected in case of efficient rise of UV penetration re-heating the disk and thus allowing CO thermal desorption or favoring direct CO photo-desorption. CO is also detected up to 3-4 scale heights while CS is confined around 1 scale height above the mid-plane. The limits of the method due to finite spatial and spectral resolutions are also discussed. This method appears to be very promising to determine the gas structure of planet-forming disks, provided that the molecular data have an angular resolution which is high enough, of the order of 0.3−0.1" at the distance of the nearest star forming regions.

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.

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.

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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ALMA Finds Organic Compounds in Protoplanetary Disks

Two teams of astronomers have harnessed the power of the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to detect the prebiotic complex organic molecule methyl isocyanate [1] in the multiple star system IRAS 16293-2422. One team was co-led by Rafael Martín-Doménech at the Centro de Astrobiología in Madrid, Spain, and Víctor M. Rivilla, at the Osservatorio Astrofisico di Arcetri in Florence, Italy; and the other by Niels Ligterink at the Leiden Observatory in the Netherlands and Audrey Coutens at University College London, United Kingdom.

"This star system seems to keep on giving! Following the discovery of sugars, we've now found methyl isocyanate. This family of organic molecules is involved in the synthesis of peptides and amino acids, which, in the form of proteins, are the biological basis for life as we know it," explain Niels Ligterink and Audrey Coutens [2].

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Candidate Snowlines Found Around T Tauri Stars

CANDIDATE WATER VAPOR LINES TO LOCATE THE H2O SNOWLINE THROUGH HIGH-DISPERSION SPECTROSCOPIC OBSERVATIONS. I. THE CASE OF A T TAURI STAR

Authors:

Notsu et al

Abstract:

Inside the H2O snowline of protoplanetary disks, water evaporates from the dust-grain surface into the gas phase, whereas it is frozen out onto the dust in the cold region beyond the snowline. H2O ice enhances the solid material in the cold outer part of a disk, which promotes the formation of gas-giant planet cores. We can regard the H2O snowline as the surface that divides the regions between rocky and gaseous giant planet formation. Thus observationally measuring the location of the H2O snowline is crucial for understanding the planetesimal and planet formation processes, and the origin of water on Earth. In this paper, we find candidate water lines to locate the H2O snowline through future high-dispersion spectroscopic observations. First, we calculate the chemical composition of the disk and investigate the abundance distributions of H2O gas and ice, and the position of the H2O snowline. We confirm that the abundance of H2O gas is high not only in the hot midplane region inside the H2O snowline but also in the hot surface layer of the outer disk. Second, we calculate the H2O line profiles and identify those H2O lines that are promising for locating the H2O snowline: the identified lines are those that have small Einstein A coefficients and high upper state energies. The wavelengths of the candidate H2O lines range from mid-infrared to sub-millimeter, and they overlap with the regions accessible to the Atacama Large Millimeter/sub-millimeter Array and future mid-infrared high-dispersion spectrographs (e.g., TMT/MICHI, SPICA).

PROTOPLANETARY DISKS IN THE ORION OMC1 REGION IMAGED WITH ALMA

PROTOPLANETARY DISKS IN THE ORION OMC1 REGION IMAGED WITH ALMA

Authors:

Eisner et al

Abstract:

We present ALMA observations of the Orion Nebula that cover the OMC1 outflow region. Our focus in this paper is on compact emission from protoplanetary disks. We mosaicked a field containing ~600 near-IR-identified young stars, around which we can search for sub-millimeter emission tracing dusty disks. Approximately 100 sources are known proplyds identified with the Hubble Space Telescope. We detect continuum emission at 1 mm wavelengths toward ~20% of the proplyd sample, and ~8% of the larger sample of near-IR objects. The noise in our maps allows 4σ detection of objects brighter than ~1.5 mJy, corresponding to protoplanetary disk masses larger than 1.5 M J (using standard assumptions about dust opacities and gas-to-dust ratios). None of these disks are detected in contemporaneous CO(2-1) or C18O(2-1) observations, suggesting that the gas-to-dust ratios may be substantially smaller than the canonical value of 100. Furthermore, since dust grains may already be sequestered in large bodies in Orion Nebula cluster (ONC) disks, the inferred masses of disk solids may be underestimated. Our results suggest that the distribution of disk masses in this region is compatible with the detection rate of massive planets around M dwarfs, which are the dominant stellar constituent in the ONC.

Measuring protoplanetary disk gas surface density profiles with ALMA

Measuring protoplanetary disk gas surface density profiles with ALMA

Authors:

Williams et al

Abstract:

The gas and dust are spatially segregated in protoplanetary disks due to the vertical settling and radial drift of large grains. A fuller accounting of the mass content and distribution in disks therefore requires spectral line observations. We extend the modeling approach presented in Williams & Best (2014) to show that gas surface density profiles can be measured from high fidelity 13CO integrated intensity images. We demonstrate the methodology by fitting ALMA observations of the HD 163296 disk to determine a gas mass, Mgas = 0.048 solar masse, and accretion disk characteristic size Rc = 213au and gradient gamma = 0.39. The same parameters match the C18O 2--1 image and indicates an abundance ratio [13CO]/[C18O] of 700 independent of radius. To test how well this methodology can be applied to future line surveys of smaller, lower mass T Tauri disks, we create a large 13CO 2--1 image library and fit simulated data. For disks with gas masses 3-10 Jupiter masses at 150pc, ALMA observations with a resolution of 0.2-0.3 arcseconds and integration times of about 20 minutes allow reliable estimates of Rc to within about 10au and gamma to within about 0.2. Economic gas imaging surveys are therefore feasible and offer the opportunity to open up a new dimension for studying disk structure and its evolution toward planet formation.

Towards detecting methanol emission in low-mass protoplanetary discs with ALMA

Towards detecting methanol emission in low-mass protoplanetary discs with ALMA: The role of non-LTE excitation

Authors:

Parfenov et al

Abstract:

The understanding of organic content of protoplanetary discs is one of the main goals of the planet formation studies. As an attempt to guide the observational searches for weak lines of complex species in discs, we modelled the (sub-)millimetre spectrum of gaseous methanol (CH3OH), one of the simplest organic molecules, in the representative T Tauri system. We used 1+1D disc physical model coupled to the gas-grain ALCHEMIC chemical model with and without 2D-turbulent mixing. The computed CH3OH abundances along with the CH3OH scheme of energy levels of ground and excited torsional states were used to produce model spectra obtained with the non-local thermodynamic equilibrium (non-LTE) 3D line radiative transfer code LIME. We found that the modelled non-LTE intensities of the CH3OH lines can be lower by factor of >10--100 than those calculated under assumption of LTE. Though population inversion occurs in the model calculations for many (sub-)millimetre transitions, it does not lead to the strong maser amplification and noticeably high line intensities. We identify the strongest CH3OH (sub-)millimetre lines that could be searched for with the Atacama Large Millimeter Array (ALMA) in nearby discs. The two best candidates are the CH3OH 50−40 A+ (241.791 GHz) and 5−1−4−1 E (241.767 GHz) lines, which could possibly be detected with the ∼5σ signal-to-noise ratio after ∼3 hours of integration with the full ALMA array.

ALMA Observations of Circumstellar Disks in the Upper Scorpius OB Association

ALMA Observations of Circumstellar Disks in the Upper Scorpius OB Association

Authors:

Barenfeld et al

Abstract:

We present ALMA observations of 106 G-, K-, and M-type stars in the Upper Scorpius OB Association hosting circumstellar disks. With these data, we measure the 0.88 mm continuum and 12CO J=3−2 line fluxes of disks around low mass (0.14−1.66 M⊙) stars at an age of 5-11 Myr. Of the 75 primordial disks in the sample, 53 are detected in the dust continuum and 26 in CO. Of the 31 disks classified as debris/evolved transitional disks, 5 are detected in the continuum and none in CO. The lack of CO emission in approximately half of the disks with detected continuum emission can be explained if CO is optically thick but has a compact emitting area (≲40 AU), or if the CO is heavily depleted by a factor of at least ∼1000 relative to interstellar medium abundances and is optically thin. The continuum measurements are used to estimate the dust mass of the disks. We find a correlation between disk dust mass and stellar host mass consistent with a power-law relation of Mdust∝M1.67±0.37∗. Disk dust masses in Upper Sco are compared to those measured in the younger Taurus star forming region to constrain the evolution of disk dust mass. We find that the difference in the mean of log(Mdust/M∗) between Taurus and Upper Sco is 0.64±0.09, such that Mdust/M∗ is lower in Upper Sco by a factor of ∼4.5.

ALMA can Detect Gas Giant Forming Cores

Direct detection of precursors of gas giants formed by gravitational instability with the Atacama Large Millimetre/sub-millimetre Array

Authors:

Mayer et al

Abstract:

Phases of gravitational instability are expected in the early phases of disk evolution, when the disk mass is still a substantial fraction of the mass of the star. Disk fragmentation into sub-stellar objects could occur in the cold exterior part of the disk. Direct detection of massive gaseous clumps on their way to collapse into gas giant planets would offer an unprecedented test of the disk instability model. Here we use state-of-the-art 3D radiation-hydro simulations of disks undergoing fragmentation into massive gas giants, post-processed with the RADMC-3D ray-tracing code to produce dust continuum emission maps. These are then fed into the Common Astronomy Software Applications (CASA) ALMA simulator. The synthetic maps show that both overdense spiral arms and actual clumps at different stages of collapse can be detected with the Atacama Large Millimetre/sub-millimetre Array (ALMA) in the full configuration at the distance of the Ophiuchus star forming region (125 pc). The detection of clumps is particularly effective at shorter wavelengths (690 GHz) combining two resolutions with multi-scale clean. Furthermore, we show that a flux-based estimate of the mass of a protoplanetary clump can be from comparable to a factor of 3 higher than the gravitationally bound clump mass. The estimated mass depends on the assumed opacity, and on the gas temperature, which should be set using the input of radiation-hydro simulations. We conclude that ALMA has the capability to detect "smoking gun" systems that are a signpost of the disk instability model for gas giant planet formation.

Protoplanetary Disks in the Orion OMC1 Region Imaged with ALMA

Protoplanetary Disks in the Orion OMC1 Region Imaged with ALMA

Authors:

Eisner et al

Abstract:

We present ALMA observations of the Orion Nebula that cover the OMC1 outflow region. Our focus in this paper is on compact emission from protoplanetary disks. We mosaicked a field containing ∼600 near-IR-identified young stars, around which we can search for sub-mm emission tracing dusty disks. Approximately 100 sources are known proplyds identified with HST. We detect continuum emission at 1 mm wavelengths towards ∼20% of the proplyd sample, and ∼8% of the larger sample of near-IR objects. The noise in our maps allows 4σ detection of objects brighter than ∼1.5 mJy, corresponding to protoplanetary disk masses larger than 1.5 MJ (using standard assumptions about dust opacities and gas-to-dust ratios). None of these disks are detected in contemporaneous CO(2-1) or C18O(2-1) observations, suggesting that the gas-to-dust ratios may be substantially smaller than the canonical value of 100. Furthermore, since dust grains may already be sequestered in large bodies in ONC disks, the inferred masses of disk solids may be underestimated. Our results suggest that the distribution of disk masses in this region is compatible with the detection rate of massive planets around M dwarfs, which are the dominant stellar constituent in the ONC.

Constraining turbulence mixing strength in transitional discs with planets using SPHERE and ALMA

Constraining turbulence mixing strength in transitional discs with planets using SPHERE and ALMA

Authors:

de Juan Ovelar et al

Abstract:

We investigate the effect that the turbulent mixing strength parameter αturb plays on near-infrared polarimetric and sub-millimetre interferometric imaging observations of transitional discs (TDs) with a gap carved by a planet. We generate synthetic observations of these objects with ALMA and VLT/SPHERE-ZIMPOL by combining hydrodynamical, dust evolution, radiative transfer and instrument models for values of αturb=[10−4,10−3,10−2]. We find that, through a combination of effects on the viscosity of the gas, the turbulent mixing and dust evolution processes, αturb strongly affects the morphology of the dust distribution that can be traced with these observations. We constrain the value of αturb to be within an order of magnitude of 10−3 in TD sources that show cavities in sub-mm continuum images while featuring continuous distribution of dust or smaller cavities in NIR-polarimetric images.

Resolving the Planetesimal Belt of HR 8799 with ALMA

Resolving the Planetesimal Belt of HR 8799 with ALMA

Authors:

Booth et al

Abstract:

The star HR 8799 hosts one of the largest known debris discs and at least four giant planets. Previous observations have found evidence for a warm belt within the orbits of the planets, a cold planetesimal belt beyond their orbits and a halo of small grains. With the infrared data, it is hard to distinguish the planetesimal belt emission from that of the grains in the halo. With this in mind, the system has been observed with ALMA in band 6 (1.34 mm) using a compact array format. These observations allow the inner edge of the planetesimal belt to be resolved for the first time. A radial distribution of dust grains is fitted to the data using an MCMC method. The disc is best fit by a broad ring between 145+12−12 AU and 429+37−32 AU at an inclination of 40+5−6{\deg} and a position angle of 51+8−8{\deg}. A disc edge at ~145 AU is too far out to be explained simply by interactions with planet b, requiring either a more complicated dynamical history or an extra planet beyond the orbit of planet b.