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See detailDynamical Evidence of a Spiral Arm-driving Planet in the MWC 758 Protoplanetary Disk
Ren, Bin; Dong, Ruobing; van Holstein, Rob G. et al

in Astrophysical Journal (2020), 898

More than a dozen young stars host spiral arms in their surrounding protoplanetary disks. The excitation mechanisms of such arms are under debate. The two leading hypotheses—companion-disk interaction and ... [more ▼]

More than a dozen young stars host spiral arms in their surrounding protoplanetary disks. The excitation mechanisms of such arms are under debate. The two leading hypotheses—companion-disk interaction and gravitational instability (GI)—predict distinct motion for spirals. By imaging the MWC 758 spiral arm system at two epochs spanning ∼5 yr using the SPHERE instrument on the Very Large Telescope, we test the two hypotheses for the first time. We find that the pattern speeds of the spirals are not consistent with the GI origin. Our measurements further evince the existence of a faint "missing planet" driving the disk arms. The average spiral pattern speed is 0°22 ± 0°03 yr[SUP]-1[/SUP], pointing to a driver at ${172}_{-14}^{+18}$ au around a 1.9 M[SUB]☉[/SUB] central star if it is on a circular orbit. In addition, we witness time-varying shadowing effects on a global scale that are likely originating from an inner disk. [less ▲]

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See detailFirst resolved observations of a highly asymmetric debris disc around HD 160305 with VLT/SPHERE
Perrot, Clément; Thebault, Philippe; Lagrange, Anne-Marie et al

in Astronomy and Astrophysics (2019), 626

Context. Direct imaging of debris discs gives important information about their nature, their global morphology, and allows us to identify specific structures possibly in connection with the presence of ... [more ▼]

Context. Direct imaging of debris discs gives important information about their nature, their global morphology, and allows us to identify specific structures possibly in connection with the presence of gravitational perturbers. It is the most straightforward technique to observe planetary systems as a whole. <BR /> Aims: We present the first resolved images of the debris disc around the young F-type star HD 160305, detected in scattered light using the VLT/SPHERE instrument in the near infrared. <BR /> Methods: We used a post-processing method based on angular differential imaging and synthetic images of debris discs produced with a disc modelling code (GRaTer) to constrain the main characteristics of the disc around HD 160305. All of the point sources in the field of the IRDIS camera were analysed with an astrometric tool to determine whether they are bound objects or background stars. <BR /> Results: We detect a very inclined ( 82°) ring-like debris disc located at a stellocentric distance of about 86 au (deprojected width 27 au). The disc displays a brightness asymmetry between the two sides of the major axis, as can be expected from scattering properties of dust grains. We derive an anisotropic scattering factor g > 0.5. A second right-left asymmetry is also observed with respect to the minor axis. We measure a surface brightness ratio of 0.73 ± 0.18 between the bright and the faint sides. Because of the low signal-to-noise ratio (S/N) of the images we cannot easily discriminate between several possible explanations for this left-right asymmetry, such as perturbations by an unseen planet, the aftermath of the breakup of a massive planetesimal, or the pericenter glow effect due to an eccentric ring. Two epochs of observations allow us to reject the companionship hypothesis for the 15 point sources present in the field. <P />The reduced images (FITS files) are only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz- bin/qcat?J/A+A/626/A95">http://cdsarc.u-strasbg.fr/viz- bin/qcat?J/A+A/626/A95</A>Based on observations made with ESO Telescopes at the Paranal Observatory under programs ID 95.C-0298 and 97.C-0865.Note to the reader: The name of the author "Jean-Charles Ausgereau" was a mistake and has been corrected in "Jean-Charles Augereau" on 3 July 2019. [less ▲]

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See detailThree Years of SPHERE: The Latest View of the Morphology and Evolution of Protoplanetary Discs
Garufi, Antonio; Benisty, Myriam; Stolker, Tomas et al

in Messenger (2017), 169

Spatially resolving the immediate surroundings of young stars is a key challenge for the planet formation community. SPHERE on the VLT represents an important step forward by increasing the opportunities ... [more ▼]

Spatially resolving the immediate surroundings of young stars is a key challenge for the planet formation community. SPHERE on the VLT represents an important step forward by increasing the opportunities offered by optical or near-infrared imaging instruments to image protoplanetary discs. The Guaranteed Time Observation Disc team has concentrated much of its efforts on polarimetric differential imaging, a technique that enables the efficient removal of stellar light and thus facilitates the detection of light scattered by the disc within a few au from the central star. These images reveal intriguing complex disc structures and diverse morphological features that are possibly caused by ongoing planet formation in the disc. An overview of the recent advances enabled by SPHERE is presented. <P /> [less ▲]

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See detailSpiral Arms in the Disk of HD 142527
Christiaens, Valentin ULiege; Casassus, Simon; Pérez, Sebastian et al

in Astronomical Society of the Pacific Conference Series (2015, December), 499

In view of its large gap, previously reported asymmetries and near-infrared (NIR) spiral arms, the transition disk of the Herbig Fe star HD 142527 constitutes a remarkable case study. Based on our ALMA ... [more ▼]

In view of its large gap, previously reported asymmetries and near-infrared (NIR) spiral arms, the transition disk of the Herbig Fe star HD 142527 constitutes a remarkable case study. Based on our ALMA observations of the disk and previous NIR images, we try to infer the origin of the observed spirals. Different scenarios, including the effect of the binary companion, unseen planets, disk self-gravity and tidal interaction by a stellar encounter, are discussed in order to constrain the origin of the spirals. We conclude that at least a combination of two of the considered scenarios are required to account for the large annular gap, the NIR spirals and all three CO spirals. [less ▲]

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See detailA Compact Concentration of Large Grains in the HD 142527 Protoplanetary Dust Trap
Casassus, Simon; Wright, Chris; Marino, Sebastian et al

in Astrophysical Journal (2015)

A pathway to the formation of planetesimals, and eventually giant planets, may occur in concentrations of dust grains trapped in pressure maxima. Dramatic crescent-shaped dust concentrations have been ... [more ▼]

A pathway to the formation of planetesimals, and eventually giant planets, may occur in concentrations of dust grains trapped in pressure maxima. Dramatic crescent-shaped dust concentrations have been seen in recent radio images at submillimeter wavelengths. These disk asymmetries could represent the initial phases of planet formation in the dust trap scenario, provided that grain sizes are spatially segregated. A testable prediction of azimuthal dust trapping is that progressively larger grains should be more sharply confined and should follow a distribution that is markedly different from the gas. However, gas tracers such as 12CO and the infrared emission from small grains are both very optically thick where the submillimeter continuum originates, so previous observations have been unable to test the trapping predictions or to identify compact concentrations of larger grains required for planet formation by core accretion. Here we report multifrequency observations of HD 142527, from 34 to 700 GHz, that reveal a compact concentration of grains approaching centimeter sizes, with a few Earth masses, embedded in a large-scale crescent of smaller, submillimeter-sized particles. The emission peaks at wavelengths shorter than ∼1 mm are optically thick and trace the temperature structure resulting from shadows cast by the inner regions. Given this temperature structure, we infer that the largest dust grains are concentrated in the 34 GHz clump. We conclude that dust trapping is efficient enough for grains observable at centimeter wavelengths to lead to compact concentrations. [less ▲]

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See detailFast-moving features in the debris disk around AU Microscopii
Boccaletti, Anthony; Thalmann, Christian; Lagrange, Anne-Marie et al

in Nature (2015), 526

In the 1980s, excess infrared emission was discovered around main- sequence stars; subsequent direct-imaging observations revealed orbiting disks of cold dust to be the source. These `debris disks' were ... [more ▼]

In the 1980s, excess infrared emission was discovered around main- sequence stars; subsequent direct-imaging observations revealed orbiting disks of cold dust to be the source. These `debris disks' were thought to be by-products of planet formation because they often exhibited morphological and brightness asymmetries that may result from gravitational perturbation by planets. This was proved to be true for the β Pictoris system, in which the known planet generates an observable warp in the disk. The nearby, young, unusually active late-type star AU Microscopii hosts a well-studied edge-on debris disk; earlier observations in the visible and near-infrared found asymmetric localized structures in the form of intensity variations along the midplane of the disk beyond a distance of 20 astronomical units. Here we report high- contrast imaging that reveals a series of five large-scale features in the southeast side of the disk, at projected separations of 10-60 astronomical units, persisting over intervals of 1-4 years. All these features appear to move away from the star at projected speeds of 4-10 kilometres per second, suggesting highly eccentric or unbound trajectories if they are associated with physical entities. The origin, localization, morphology and rapid evolution of these features are difficult to reconcile with current theories. [less ▲]

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See detailSpiral arms in the disk of HD 142527 with ALMA
Christiaens, Valentin ULiege; Casassus, Simon; Perez, Sebastian et al

Scientific conference (2014, April 11)

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See detailSpiral Arms in the Disk of HD 142527 from CO Emission Lines with ALMA
Christiaens, Valentin ULiege; Casassus, Simon; Perez, Sebastian et al

in Astrophysical Journal. Letters (2014), 785

In view of both the size of its gap and the previously reported asymmetries and near-infrared spiral arms, the transition disk of the Herbig Fe star HD 142527 constitutes a remarkable case study. This ... [more ▼]

In view of both the size of its gap and the previously reported asymmetries and near-infrared spiral arms, the transition disk of the Herbig Fe star HD 142527 constitutes a remarkable case study. This paper focuses on the morphology of the outer disk through ALMA observations of 12CO J = 2-1, 12CO J = 3-2, and 13CO J = 2-1. Both 12CO (2-1) and 12CO (3-2) show spiral features of different sizes. The innermost spiral arm (S1) is a radio counterpart of the first near-infrared spiral observed by Fukagawa, but it is shifted radially outward. However, the most conspicuous CO spiral arm (S2) lies at the outskirts of the disk and has not been detected before. It corresponds to a cold density structure, with both brightness and excitation temperatures of order 13±2 K and conspicuous in the 12CO (2-1) peak-intensity map, but faint in 12CO (3-2). There is also a faint counterarm (S3), at a point-symmetric location of S2 with respect to the star. These three spirals are modeled separately with two different formulae that approximate the loci of density maxima in acoustic waves due to embedded planets. S1 could be fit relatively well with these formulae, compared to S2 and S3. Alternative scenarios such as gravitational instability or external tidal interaction are discussed. The impact of channelization on spectrally and spatially resolved peak intensity maps is also briefly addressed. [less ▲]

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See detailCO spiral arms in the outer disk of HD 142527 with ALMA
Christiaens, Valentin ULiege; Casassus, Simon; Perez, Sebastian et al

Poster (2014)

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See detailCO spiral arms in the outer disk of HD 142527 with ALMA
Christiaens, Valentin ULiege; Casassus, Simon; Perez, Sebastian et al

in Iono, Daisuke; Wootten, Al; Testi, Leonardo (Eds.) REVOLUTION IN ASTRONOMY WITH ALMA: THE THIRD YEAR (2014)

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See detailThe VLTI/PIONIER survey of southern TTauri disks.
Anthonioz, Fabien; Ménard, Francois; Pinte, Christophe et al

in Protostars and Planets VI (2013, July 01)

Studying the inner regions of protoplanetary disks (1-10 AU) is of importance to understand the formation of planets and the accretion process feeding the forming central star. Herbig AeBe stars are ... [more ▼]

Studying the inner regions of protoplanetary disks (1-10 AU) is of importance to understand the formation of planets and the accretion process feeding the forming central star. Herbig AeBe stars are bright enough to be routinely observed by Near IR interferometers. The data for the fainter T Tauri stars is much more sparse. In this contribution we present the results of our ongoing survey at the VLTI. We used the PIONIER combiner that allows the simultaneous use of 4 telescopes, yielding 6 baselines and 3 independent closure phases at once. PIONIER's integrated optics technology makes it a sensitive instrument. We have observed 22 T Tauri stars so far, the largest survey for T Tauri stars to this date. Our results demonstrate the very significant contribution of an extended component to the interferometric signal. The extended component is different from source to source and the data, with several baselines, offer a way to improve our knowledge of the disk geometry and/or composition.These results validate an earlier study by Pinte et al. 2008 and show that the dust inner radii of T Tauri disks now appear to be in better agreement with the expected position of the dust sublimation radius, contrary to previous claims. [less ▲]

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See detailSpiral arms in the disk of HD 142527 from CO emission lines with ALMA
Christiaens, Valentin ULiege; Casassus, Simon; Perez, Sebastian et al

Poster (2013)

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