We present ALMA Band 6 observations of a complete sample of protoplanetary disks in the young (∼1-3 Myr) Lupus star-forming region, covering the 1.33 mm continuum and the 12 CO, 13 CO, and C 18 O J = 2-1 lines. The spatial resolution is ∼ 0. 25 with a medium 3σ continuum sensitivity of 0.30 mJy, corresponding to M dust ∼ 0.2 M ⊕ . We apply "Keplerian masking" to enhance the signalto-noise ratios of our 12 CO zero-moment maps, enabling measurements of gas disk radii for 22 Lupus disks; we find that gas disks are universally larger than mm dust disks by a factor of two on average, likely due to a combination of the optically thick gas emission as well as the growth and inward drift of the dust. Using the gas disk radii, we calculate the dimensionless viscosity parameter, α visc , finding a broad distribution and no correlations with other disk or stellar parameters, suggesting that viscous processes have not yet established quasi-steady states in Lupus disks. By combining our 1.33 mm continuum fluxes with our previous 890 µm continuum observations, we also calculate the mm spectral index, α mm , for 70 Lupus disks; we find an anti-correlation between α mm and mm flux for low-mass disks (M dust 5), followed by a flattening as disks approach α mm ≈ 2, which could indicate faster grain growth in higher-mass disks, but may also reflect their larger optically thick components. In sum, this work demonstrates the continuous stream of new insights into disk evolution and planet formation that can be gleaned from unbiased ALMA disk surveys.

The σ Orionis cluster is important for studying protoplanetary disk evolution, as its intermediate age (3)(4)(5) is comparable to the median disk lifetime. We use ALMA to conduct a high-sensitivity survey of dust and gas in 92 protoplanetary disks around σ Orionis members with M * 0.1 M . Our observations cover the 1.33 mm continuum and several CO J = 2-1 lines: out of 92 sources, we detect 37 in the mm continuum and six in 12 CO, three in 13 CO, and none in C 18 O. Using the continuum emission to estimate dust mass, we find only 11 disks with M dust 10 M ⊕ , indicating that after only a few Myr of evolution most disks lack sufficient dust to form giant planet cores. Stacking the individually undetected continuum sources limits their average dust mass to 5× lower than that of the faintest detected disk, supporting theoretical models that indicate rapid dissipation once disk clearing begins. Comparing the protoplanetary disk population in σ Orionis to those of other star-forming regions supports the steady decline in average dust mass and the steepening of the M dust -M * relation with age; studying these evolutionary trends can inform the relative importance of different disk processes during key eras of planet formation. External photoevaporation from the central O9 star is influencing disk evolution throughout the region: dust masses clearly decline with decreasing separation from the photoionizing source, and the handful of CO detections exist at projected separations > 1.5 pc. Collectively, our findings indicate that giant planet formation is inherently rare and/or well underway by a few Myr of age.

Context. Understanding the diversity of planets requires studying the morphology and physical conditions in the protoplanetary disks in which they form. Aims. We aim to study the structure of the ∼10 Myr old protoplanetary disk HD 100453, to detect features that can trace disk evolution and to understand the mechanisms that drive these features. Methods. We observed HD 100453 in polarized scattered light with SPHERE/VLT at optical (0.6 µm, 0.8 µm) and near-infrared (1.2 µm) wavelengths, reaching an angular resolution of ∼0.02 , and an inner working angle of ∼0.09 . Results. We spatially resolve the disk around HD 100453, and detect polarized scattered light up to ∼0.42 (∼48 au). We detect a cavity, a rim with azimuthal brightness variations at an inclination of ∼38• with respect to our line of sight, two shadows and two symmetric spiral arms. The spiral arms originate near the location of the shadows, close to the semi major axis. We detect a faint feature in the SW that can be interpreted as the scattering surface of the bottom side of the disk, if the disk is tidally truncated by the M-dwarf companion currently seen at a projected distance of ∼119 au. We construct a radiative transfer model that accounts for the main characteristics of the features with an inner and outer disk misaligned by ∼72• . The azimuthal brightness variations along the rim are well reproduced with the scattering phase function of the model. While spirals can be triggered by the tidal interaction with the companion, the close proximity of the spirals to the shadows suggests that the shadows could also play a role. The change in stellar illumination along the rim induces an azimuthal variation of the scale height that can contribute to the brightness variations. Conclusions. Dark regions in polarized images of transition disks are now detected in a handful of disks and often interpreted as shadows due to a misaligned inner disk. However, the origin of such a misalignment in HD 100453, and of the spirals, is still unclear, and might be due to a yet-undetected massive companion inside the cavity, and on an inclined orbit. Observations over a few years will allow us to measure the spiral pattern speed, and determine if the shadows are fixed or moving, which may constrain their origin.

Context. Imaged in the gap of a transition disk and found at a separation of about 195 mas (∼22 au) from its host star at a position angle of about 155 o , PDS 70 b is the most robustly detected young planet to date. This system is therefore a unique laboratory for characterizing the properties of young planetary systems at the stage of their formation. Aims. We aim to trace direct and indirect imprints of PDS 70 b on the gas and dust emission of the circumstellar disk in order to study the properties of this ∼5 Myr young planetary system. Methods. We obtained ALMA band 7 observations of PDS 70 in dust continuum and 12 CO (3 − 2) and combined them with archival data. This resulted in an unprecedented angular resolution of about 70 mas (∼8 au). Results. We derive an upper limit on circumplanetary material at the location of PDS 70 b of ∼0.01 M ⊕ and find a highly structured circumstellar disk in both dust and gas. The outer dust ring peaks at 0.65 (74 au) and reveals a possible second unresolved peak at about 0.53 (60 au). The integrated intensity of CO also shows evidence of a depletion of emission at ∼0.2 (23 au) with a width of ∼0.1 (11 au). The gas kinematics show evidence of a deviation from Keplerian rotation inside 0.8 (91 au). This implies a pressure gradient that can account for the location of the dust ring well beyond the location of PDS 70 b. Farther in, we detect an inner disk that appears to be connected to the outer disk by a possible bridge feature in the northwest region in both gas and dust. We compare the observations to hydrodynamical simulations that include a planet with different masses that cover the estimated mass range that was previously derived from near-infrared photometry (∼5-9 M Jup ). We find that even a planet with a mass of 10 M Jup may not be sufficient to explain the extent of the wide gap, and an additional low-mass companion may be needed to account for the observed disk morphology.

We estimate the mass loss rates of photoevaporative winds launched from the outer edge of protoplanetary discs impinged by an ambient radiation field. We focus on mild/moderate environments (the number of stars in the group/cluster is N 50), and explore disc sizes ranging between 20 and 250 AU. We evaluate the steady-state structures of the photoevaporative winds by coupling temperature estimates obtained with a PDR code with 1D radial hydrodynamical equations. We also consider the impact of dust dragging and grain growth on the final mass loss rates. We find that these winds are much more significant than have been appreciated hitherto when grain growth is included in the modelling: in particular, mass loss rates 10 −8 M /yr are predicted even for modest background field strengths ( 30 G 0 ) in the case of discs that extend to R > 150 AU. Grain growth significantly affects the final mass loss rates by reducing the average cross section at FUV wavelengths, and thus allowing a much more vigorous flow. The radial profiles of observable quantities (in particular surface density, temperature and velocity patterns) indicate that these winds have characteristic features that are now potentially observable with ALMA. In particular, such discs should have extended gaseous emission that is dust depleted in the outer regions, characterised by a non-Keplerian rotation curve, and with a radially increasing temperature gradient.