Protoplanets and circumplanetary disks are rather elusive in their thermal IR emission. Yet they are cornerstones to the most popular interpretations for the protoplanetary disk structures observed ...in the gas and dust density fields, even though alternative theories exist. The gaseous velocity field should also bear the imprint of planet-disk interactions, with non-Keplerian fine structure in the molecular-line channel maps. Such kinks or wiggles are affected by the optical depth structure and synthesis imaging limitations, but their detail could in principle be connected to the perturber by comparison with hydrodynamical simulations. These predictions appear to have been observed in HD 163296 and HD 97048, where the most conspicuous wiggles are interpreted in terms of embedded planets. The velocity centroid maps may allow for more robust indirect detections of embedded planets. The non-Keplerian velocity along the planetary wakes undergoes an abrupt sign reversal across the protoplanet. After subtraction of the disk rotation curve, the location of the perturber should be identifiable as a Doppler flip in velocity centroid maps. Here we improve our rotation curves in an extension to disks with intermediate inclinations, which we apply to deep and fine angular resolution CO isotopologue data sets. Trials in HD 163296 and in HD 97048 yield nondetections. However, in HD 100546 we pick up a conspicuous Doppler flip, an important part of which is likely due to radial flows. Its coincidence with a fine ridge crossing an annular groove inside the continuum ring suggests a complex dynamical scenario, in which the putative protoplanet might have recently undergone pebble accretion.
Object Lessons is a series of short, beautifully designed books about the hidden lives of ordinary things. The story of the compact disc is also the story of the end of physical media. It is the ...story of how the quest for perfection laid the grounds for the death of a great industry. For in the passage from analogue media, like records and tapes, to digital formats, like CDs, something changed in the nature of media and in the relationship we have with music. Music became code, a sequence of 1s and 0s, a flow of pure information. The material structure of the medium itself was always supposed to disappear. But the physical has proved to possess an uncanny knack for returning. Today the CD is a zombie medium, still popular amongst certain avant-garde record labels and Japanese consumers. Against all the odds, the spectre endures. Object Lessons is published in partnership with an essay series in The Atlantic.
Thanatology in protoplanetary discs Lesur, Geoffroy; Kunz, Matthew W; Fromang, Sebastien
Astronomy and astrophysics (Berlin),
06/2014, Volume:
566
Journal Article
Peer reviewed
Open access
Protoplanetary discs are poorly ionised due to their low temperatures and high column densities and are therefore subject to three "non-ideal" magnetohydrodynamic (MHD) effects: Ohmic dissipation, ...ambipolar diffusion, and the Hall effect. The existence of magnetically driven turbulence in these discs has been a central question since the discovery of the magnetorotational instability (MRI). Recent work has suggested that a combination of Ohmic dissipation and ambipolar diffusion can render both the midplane and surface layers of the disc inactive and that torques due to magnetically driven outflows are required to explain the observed accretion rates. We reassess this picture by performing three-dimensional numerical simulations that include all three non-ideal MHD effects for the first time. The results demonstrate that if the MRI is relevant for driving mass accretion in protoplanetary discs, one must include the Hall effect to obtain even qualitatively correct results.
ABSTRACT The identification of ongoing planet formation requires the finest angular resolutions and deepest sensitivities in observations inspired by state-of-the-art numerical simulations. ...Hydrodynamic simulations of planet-disk interactions predict the formation of circumplanetary disks (CPDs) around accreting planetary cores. These CPDs have eluded unequivocal detection-their identification requires predictions in CPD tracers. In this work, we aim to assess the observability of embedded CPDs with the Atacama Large Millimeter/submillimeter Array (ALMA) as features imprinted in the gas kinematics. We use 3D smooth particle hydrodynamic simulations of CPDs around 1 and 5 planets at large stellocentric radii in locally isothermal and adiabatic disks. The simulations are then connected with 3D radiative transfer for predictions in CO isotopologues. Observability is assessed by corrupting with realistic long baseline phase noise extracted from the recent HL Tau ALMA data. We find that the presence of a CPD produces distinct signposts: (1) a compact emission separated in velocity from the overall circumstellar disk's Keplerian pattern, (2) a strong impact on the velocity pattern when the Doppler-shifted line emission sweeps across the CPD location, and (3) a local increase in the velocity dispersion. We test our predictions with a simulation tailored for HD 100546-which has a reported protoplanet candidate. We find that the CPDs are detectable in all three signposts with ALMA Cycle 3 capabilities for both 1 and 5 protoplanets, when embedded in an isothermal disk.
We analyze the dust morphology of 29 transition disks (TDs) observed with Atacama Large (sub-)Millimeter Array (ALMA) at (sub-)millimeter emission. We perform the analysis in the visibility plane to ...characterize the total flux, cavity size, and shape of the ring-like structure. First, we found that the Mdust-M relation is much flatter for TDs than the observed trends from samples of class II sources in different star-forming regions. This relation demonstrates that cavities open in high (dust) mass disks, independent of the stellar mass. The flatness of this relation contradicts the idea that TDs are a more evolved set of disks. Two potential reasons (not mutually exclusive) may explain this flat relation: the emission is optically thick or/and millimeter-sized particles are trapped in a pressure bump. Second, we discuss our results of the cavity size and ring width in the context of different physical processes for cavity formation. Photoevaporation is an unlikely leading mechanism for the origin of the cavity of any of the targets in the sample. Embedded giant planets or dead zones remain as potential explanations. Although both models predict correlations between the cavity size and the ring shape for different stellar and disk properties, we demonstrate that with the current resolution of the observations, it is difficult to obtain these correlations. Future observations with higher angular resolution observations of TDs with ALMA will help discern between different potential origins of cavities in TDs.
To characterize the substructures induced in protoplanetary disks by the interaction between stars in multiple systems, we study the 1.25 mm continuum and the 12CO(J = 2-1) spectral line emission of ...the triple systems HT Lup and AS 205, at scales of 5 au, as part of the "Disk Substructures at High Angular Resolution Project" (DSHARP). In the continuum emission, we find two symmetric spiral arms in the disk around AS 205 N, with a pitch angle of 14°, while the southern component AS 205 S, itself a spectroscopic binary, is surrounded by a compact inner disk and a bright ring at a radius of 34 au. The 12CO line exhibits clear signatures of tidal interactions, with spiral arms, extended arc-like emission, and high velocity gas, possible evidence of a recent close encounter between the disks in the AS 205 system, as these features are predicted by hydrodynamic simulations of flyby encounters. In the HT Lup system, we detect continuum emission from all three components. The primary disk, HT Lup A, also shows a two-armed symmetric spiral structure with a pitch angle of 4°, while HT Lup B and C, located at 25 and 434 au in projected separation from HT Lup A, are barely resolved with ∼5 and ∼10 au in diameter, respectively. The gas kinematics for the closest pair indicates a different sense of rotation for each disk, which could be explained by either a counter rotation of the two disks in different, close to parallel, planes, or by a projection effect of these disks with a close to 90° misalignment between them.
Aims. We investigate the evolution of protoplanetary discs (PPDs) with magnetically driven disc winds and viscous heating. Methods. We considered an initially massive disc with ~0.1 M⊙ to track the ...evolution from the early stage of PPDs. We solved the time evolution of surface density and temperature by taking into account viscous heating and the loss of mass and angular momentum by the disc winds within the framework of a standard α model for accretion discs. Our model parameters, turbulent viscosity, disc wind mass-loss, and disc wind torque, which were adopted from local magnetohydrodynamical simulations and constrained by the global energetics of the gravitational accretion, largely depends on the physical condition of PPDs, particularly on the evolution of the vertical magnetic flux in weakly ionized PPDs. Results. Although there are still uncertainties concerning the evolution of the vertical magnetic flux that remains, the surface densities show a large variety, depending on the combination of these three parameters, some of which are very different from the surface density expected from the standard accretion. When a PPD is in a wind-driven accretion state with the preserved vertical magnetic field, the radial dependence of the surface density can be positive in the inner region <1−10 au. The mass accretion rates are consistent with observations, even in the very low level of magnetohydrodynamical turbulence. Such a positive radial slope of the surface density strongly affects planet formation because it inhibits the inward drift or even causes the outward drift of pebble- to boulder-sized solid bodies, and it also slows down or even reversed the inward type-I migration of protoplanets. Conclusions. The variety of our calculated PPDs should yield a wide variety of exoplanet systems.
We present the first kinematical detection of embedded protoplanets within a protoplanetary disk. Using archival Atacama Large Millimetre Array (ALMA) observations of HD 163296, we demonstrate a new ...technique to measure the rotation curves of CO isotopologue emission to sub-percent precision relative to the Keplerian rotation. These rotation curves betray substantial deviations caused by local perturbations in the radial pressure gradient, likely driven by gaps carved in the gas surface density by Jupiter-mass planets. Comparison with hydrodynamic simulations shows excellent agreement with the gas rotation profile when the disk surface density is perturbed by two Jupiter-mass planets at 83 and 137 au. As the rotation of the gas is dependent upon the pressure of the total gas component, this method provides a unique probe of the gas surface density profile without incurring significant uncertainties due to gas-to-dust ratios or local chemical abundances that plague other methods. Future analyses combining both methods promise to provide the most accurate and robust measures of embedded planetary mass. Furthermore, this method provides a unique opportunity to explore wide-separation planets beyond the mm continuum edge and to trace the gas pressure profile essential in modeling grain evolution in disks.
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