Abstract: The (CO)-C-12 rotational lines in protoplanetary discs are good tracers of the total spatial extension of the gas component, and potentially planet-disc interactions. We present ALMA long baseline observations of the (CO)-C-12(2-1) line of 10 protoplanetary discs from the Ophiuchus DIsc Survey Employing ALMA (ODISEA) project, aiming to set constraints on the gas distribution of these sources. The position angle of the gaseous disc can be inferred for five sources using high-velocity channels, which trace the gas in the inner part of the disc. We compare the high-velocity PAs to the orientations inferred from the continuum, representative of the orientation over similar to 53 to 256 au in these resolved discs. We find a significant difference in orientation for DoAr 44, which is evidence of a tilted inner disc. Eight discs show evidence of gas inside inner dust cavities or gaps, and the disc of ISO-Oph 196 is not detected in (CO)-C-12(2-1), except for the compact signal located inside its dust cavity. Our observations also point out a possible outflow in WLY 2-63.

Abstract: Planet-disc interactions build up local pressure maxima that may halt the radial drift of protoplanetary dust, and pile it up in rings and crescents. ALMA observations of the HD 135344B disc revealed two rings in the thermal continuum stemming from similar to mm-sized dust. At higher frequencies the inner ring is brighter relative to the outer ring, which is also shaped as a crescent rather than a full ring. In near-IR scattered light images, the disc is modulated by a two-armed grand-design spiral originating inside the ALMA inner ring. Such structures may be induced by a massive companion evacuating the central cavity, and by a giant planet in the gap separating both rings, that channels the accretion of small dust and gas through its filamentary wakes while stopping the larger dust from crossing the gap. Here we present ALMA observations in the J = (2 – 1) CO isotopologue lines and in the adjacent continuum, with up to 12 km baselines. Angular resolutions of similar to 0 ''.03 reveal the tentative detection of a filament connecting both rings, and which coincides with a local discontinuity in the pitch angle of the IR spiral, proposed previously as the location of the protoplanet driving this spiral. Line diagnostics suggests that turbulence, or superposed velocity components, is particularly strong in the spirals. The (CO)-C-12(2-1) 3D rotation curve points at stellocentric accretion at radii within the inner dust ring, with a radial velocity of up to similar to 5 per cent +/- 0.5 per cent Keplerian, which corresponds to an excessively large accretion rate of similar to 2 x 10(-6) M circle dot yr(-1) if all of the CO layer follows the (CO)-C-12(2-1) kinematics. This suggests that only the surface layers of the disc are undergoing accretion, and that the line broadening is due to superposed laminar flows.

Abstract: Substructures in protoplanetary disks can act as dust traps that shape the radial distribution of pebbles. By blocking the passage of pebbles, the presence of gaps in disks may have a profound effect on pebble delivery into the inner disk, crucial for the formation of inner planets via pebble accretion. This process can also affect the delivery of volatiles (such as H2O) and their abundance within the water snow line region (within a few au). In this study, we aim to understand what effect the presence of gaps in the outer gas disk may have on water vapor enrichment in the inner disk. Building on previous work, we employ a volatile-inclusive disk evolution model that considers an evolving ice-bearing drifting dust population, sensitive to dust traps, which loses its icy content to sublimation upon reaching the snow line. We find that the vapor abundance in the inner disk is strongly affected by the fragmentation velocity (v( f)) and turbulence, which control how intense vapor enrichment from pebble delivery is, if present, and how long it may last. Generally, for disks with low to moderate turbulence (a = 1 x 10(-3)) and a range of v( f), radial locations and gap depths (especially those of the innermost gaps) can significantly alter enrichment. Shallow inner gaps may continuously leak material from beyond it, despite the presence of additional deep outer gaps. We finally find that for realistic v( f) (=10 m s(-1)), the presence of gaps is more important than planetesimal formation beyond the snow line in regulating pebble and volatile delivery into the inner disk.

Abstract: We review recent works on the dynamics of circumbinary accretion, including time variability, angular momentum transfer between the disk and the binary, and the secular evolution of accreting binaries. These dynamics impact stellar binary formation/evolution, circumbinary planet formation/migration, and the evolution of (super)massive black hole binaries. We discuss the dynamics and evolution of inclined/warped circumbinary disks and connect with observations of protoplanetary disks. A special kind of circumbinary accretion involves binaries embedded in big disks, which may contribute to the mergers of stellar-mass black holes in AGN disks. Highlights include the following:
Circumbinary accretion is highly variable, being modulated at P-b (the binary period) or similar to 5P(b), depending on the binary eccentricity e(b) and mass ratio q(b).
The inner region of the circumbinary disk can develop coherent eccentric structure, which may modulate the accretion and affect the physical processes (e.g., planet migration) taking place in the disk.
Over long timescales, circumbinary accretion steers binaries toward equal masses, and it does not always lead to binary orbital decay. The secular orbital evolution depends on the binary parameters (e(b) and q(b)) and on the thermodynamic properties of the accreting gas.
A misaligned disk around a low-eccentricity binary tends to evolve toward coplanarity due to viscous dissipation. But when e(b) is significant, the disk can evolve toward “polar alignment,” with the disk plane perpendicular to the binary plane.

Abstract: Episodic accretion is a low-mass pre-main sequence phenomenon characterized by sudden outbursts of enhanced accretion. These objects are classified into two: protostars with elevated levels of accretion that lasts for decades or more, called FUors, and protostars with shorter and repetitive bursts, called EXors. HBC 494 is a FUor object embedded in the Orion Molecular Cloud. Earlier Atacama Large (sub-)Millimeter Array (ALMA) continuum observations showed an asymmetry in the disc at 0.“2 resolution. Here, we present follow-up observations at similar to 0.”03, resolving the system into two components: HBC 494 N (primary) and HBC 494 S (secondary). No circumbinary disc was detected. Both discs are resolved with a projected separation of similar to 0."18 (75 au). Their projected dimensions are 84 +/- 1.8 x66.9 +/- 1.5 mas for HBC 494 N and 64.6 +/- 2.5 x46.0 +/- 1.9 mas for HBC 494 S. The discs are almost aligned and with similar inclinations. The observations show that the primary is similar to 5 times brighter/more massive and similar to 2 times bigger than the secondary. We notice that the northern component has a similar mass to the FUors, while the southern has to EXors. The HBC 494 discs show individual sizes that are smaller than single eruptive YSOs. In this work, we also report (CO)-C-12, (CO)-C-13, and (CO)-O-18 molecular line observations. At large scale, the (CO)-C-12 emission shows bipolar outflows, while the (CO)-C-13 and (CO)-O-18 maps show a rotating and infalling envelope around the system. At a smaller scale, the (CO)-C-12 and (CO)-C-13 moment zero maps show cavities within the continuum discs' area, which may indicate continuum over-subtraction or slow-moving jets and chemical destruction along the line of sight.

Abstract: Context. The C/O ratio as traced with C2H emission in protoplanetary disks is fundamental for constraining the formation mechanisms of exoplanets and for our understanding of volatile depletion in disks, but current C2H observations show an apparent bimodal distribution that is not well understood, indicating that the C/O distribution is not described by a simple radial dependence. Aims. The transport of icy pebbles has been suggested to alter the local elemental abundances in protoplanetary disks through settling, drift, and trapping in pressure bumps, resulting in a depletion of volatiles in the surface layer and an increase in the elemental C/O. Methods. We combine all disks with spatially resolved ALMA C2H observations with high-resolution continuum images and constraints on the CO snow line to determine if the C2H emission is indeed related to the location of the icy pebbles. Results. We report a possible correlation between the presence of a significant CO-ice dust reservoir and high C2H emission, which is only found in disks with dust rings outside the CO snow line. In contrast, compact dust disks (without pressure bumps) and warm transition disks (with their dust ring inside the CO snow line) are not detected in C2H, suggesting that such disks may have never contained a significant CO ice reservoir. Conclusions. This correlation provides evidence for the regulation of the C/O profile by the complex interplay of CO snow line and pressure bump locations in the disk. These results demonstrate the importance of including dust transport in chemical disk models for a proper interpretation of exoplanet atmospheric compositions and a better understanding of volatile depletion in disks, in particular the use of CO isotopologs to determine gas surface densities.