The Disk Substructures at High Angular Resolution Project (DSHARP) used ALMA to map the 1.25 mm continuum of protoplanetary disks at a spatial resolution of similar to 5 au. We present a systematic analysis of annular substructures in the 18 single-disk systems targeted in this survey. No dominant architecture emerges from this sample;instead, remarkably diverse morphologies are observed. Annular substructures can occur at virtually any radius where millimeter continuum emission is detected and range in widths from a few astronomical units to tens of astronomical units. Intensity ratios between gaps and adjacent rings range from near-unity to just a few percent. In a minority of cases, annular substructures coexist with other types of substructures, including spiral arms (3/18) and crescent-like azimuthal asymmetries (2/18). No clear trend is observed between the positions of the substructures and stellar host properties. In particular, the absence of an obvious association with stellar host luminosity (and hence the disk thermal structure) suggests that substructures do not occur preferentially near major molecular snowlines. Annular substructures like those observed in DSHARP have long been hypothesized to be due to planet-disk interactions. A few disks exhibit characteristics particularly suggestive of this scenario, including substructures in possible mean-motion resonance and "double gap" features reminiscent of hydrodynamical simulations of multiple gaps opened by a planet in a low-viscosity disk.

/pdf/the-disk-substructures-at-high-angular-resolution-project-1naxfw01n1.pdf

The Disk Substructures at High Angular Resolution Project (DSHARP). II. Characteristics of Annular Substructures

Planets form and obtain their compositions in dust and gas-rich disks around young stars, and the outcome of this process is intimately linked to the disk chemical properties. The distributions of molecules across disks regulate the elemental compositions of planets, including C/N/O/S ratios and metallicity (O/H and C/H), as well as access to water and prebiotically relevant organics. Emission from molecules also encodes information on disk ionization levels, temperature structures, kinematics, and gas surface densities, which are all key ingredients of disk evolution and planet formation models. The Molecules with ALMA at Planet-forming Scales (MAPS) ALMA Large Program was designed to expand our understanding of the chemistry of planet formation by exploring disk chemical structures down to 10 au scales. The MAPS program focuses on five disks - around IM Lup, GM Aur, AS 209, HD 163296, and MWC 480 - in which dust substructures are detected and planet formation appears to be ongoing. We observed these disks in 4 spectral setups, which together cover ~50 lines from over 20 different species. This paper introduces the ApJS MAPS Special Issue by presenting an overview of the program motivation, disk sample, observational details, and calibration strategy. We also highlight key results, including discoveries of links between dust, gas, and chemical sub-structures, large reservoirs of nitriles and other organics in the inner disk regions, and elevated C/O ratios across most disks. We discuss how this collection of results is reshaping our view of the chemistry of planet formation.

https://robots.iopscience.iop.org/article/10.3847/1538-4365/ac1432/pdf

Molecules with ALMA at Planet-forming Scales (MAPS). I. Program Overview and Highlights

Context. Dozens of protoplanetary disks have been imaged in scattered light during the last decade. Aims. The variety of brightness, extension, and morphology from this census motivates a taxonomical study of protoplanetary disks in polarimetric light to constrain their evolution and establish the current framework of this type of observation. Methods. We classified 58 disks with available polarimetric observations into six major categories (Ring, Spiral, Giant, Rim, Faint, and Small disks) based on their appearance in scattered light. We re-calculated the stellar and disk properties from the newly available Gaia DR2 and related these properties with the disk categories. Results. More than half of our sample shows disk substructures. For the remaining sources, the absence of detected features is due to their faintness, their small size, or the disk geometry. Faint disks are typically found around young stars and typically host no cavity. There is a possible dichotomy in the near-infrared (NIR) excess of sources with spiral-disks (high) and ring-disks (low). Like spirals, shadows are associated with a high NIR excess. If we account for the pre-main sequence evolutionary timescale of stars with different mass, spiral arms are likely associated with old disks. We also found a loose, shallow declining trend for the disk dust mass with time. Conclusions. Protoplanetary disks may form substructures like rings very early in their evolution but their detectability in scattered light is limited to relatively old sources ( ≳5 Myr) where the recurrently detected disk cavities cause the outer disk to be illuminate. The shallow decrease of disk mass with time might be due to a selection effect, where disks observed thus far in scattered light are typically massive, bright transition disks with longer lifetimes than most disks. Our study points toward spirals and shadows being generated by planets of a fraction of a Jupiter mass to a few Jupiter masses in size that leave their (observed) imprint on both the inner disk near the star and the outer disk cavity.

/pdf/evolution-of-protoplanetary-disks-from-their-taxonomy-in-528r5nxcnq.pdf

Evolution of protoplanetary disks from their taxonomy in scattered light: spirals, rings, cavities, and shadows

We analyze a sample of 12 HST-selected edge-on protoplanetary disks for which the vertical extent of the emission layers can be constrained directly. We present ALMA high angular resolution continuum images (0.1arcsec) of these disks at two wavelengths, 0.89mm and 2.06mm (respectively ALMA bands 7 and 4), supplemented with archival band 6 data (1.33mm) where available. For most sources, the millimeter continuum emission is more compact than the scattered light, both in the vertical and radial directions. Six sources are resolved along their minor axis in at least one millimeter band, providing direct information on the vertical distribution of the millimeter grains. For the second largest disk of the sample, the significant difference in vertical extent between band 7 and band 4 suggests efficient size-selective vertical settling of large grains. Furthermore, the only Class I object in our sample shows evidence of flaring in the millimeter. Along the major axis, all disks are well resolved. Four of them are larger in band 7 than in band 4 in the radial direction, and three have a similar radial extent in all bands. For all disks, we also derive the millimeter brightness temperature and spectral index maps. We find that the disks are likely optically thick and that the dust emission reveals low brightness temperatures in most cases (<10K). The integrated spectral indices are similar to those of disks at lower inclination. The comparison of a generic radiative transfer disk model with our data shows that at least 3 disks are consistent with a small millimeter dust scale height, of a few au (measured at r=100au). This is in contrast with the more classical value of h_g\sim10au derived from scattered light images and from gas line measurements. These results confirm, by direct observations, that large (millimeter) grains are subject to significant vertical settling in protoplanetary disks.

/pdf/observations-of-edge-on-protoplanetary-disks-with-alma-i-1z4aqpak2o.pdf

Observations of edge-on protoplanetary disks with ALMA I. Results from continuum data

ALMA observations of protoplanetary disks acquired by the Disk Substructure at High Angular Resolution Project (DSHARP) resolve the dust and gas emission on angular scales as small as 3 astronomical units, offering an unprecedented detailed view of the environment where planets form. In this article, we present and discuss observations of the HD 163296 protoplanetary disk that imaged the 1.25 mm dust continuum and $^{12}$CO J=2-1 rotational line emission at a spatial resolution of 4 and 10 au, respectively. The continuum observations resolve and allow us to characterize the previously discovered dust rings at radii of 67 and 100 au. They also reveal new small scale structures, such as a dark gap at 10 au, a bright ring at 15 au, a dust crescent at a radius of 55 au, and several fainter azimuthal asymmetries. The observations of the CO and dust emission inform about the vertical structure of the disk and allow us to directly constrain the dust extinction optical depth at the dust rings. Furthermore, the observed asymmetries in the dust continuum emission corroborate to the hypothesis that the complex structure of the HD 163296 disk is the result of the gravitational interaction with yet unseen planets.

The Disk Substructures at High Angular Resolution Project (DSHARP) - IX. A high definition study of the HD 163296 planet forming disk

ESO 
CNRS (France) 
MPIA (Germany) 
INAF (Italy) 
FINES (Switzerland) 
NOVA (The Netherlands) 
European Commission 	
RII3-Ct-2004-001566 
226604 
312430 
Netherlands Organisation for Scientific Research (NWO) TOP-1 grant as part of the research program "Herbig Ae/Be stars, Rosetta stones for understanding the formation of planetary systems" 	
614.001.552 
ANR of France 	
ANR-16-CE31-0013

/pdf/dust-modeling-of-the-combined-alma-and-sphere-datasets-of-hd-hmwz7izr5u.pdf

Dust modeling of the combined ALMA and SPHERE datasets of HD 163296. Is HD 163296 really a Meeus group II disk

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Dust modeling of the combined ALMA and SPHERE datasets of HD 163296. Is HD 163296 really a Meeus group II disk