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Planet-disk interactions can produce kinematic signatures in protoplanetary disks. While recent observations have detected non-Keplerian gas motions in disks, their origins are still being debated. To explore this, we conduct 3D hydrodynamic simulations using the code FARGO3D to study non-axisymmetric kinematic perturbations at 2 scale heights induced by Jovian planets in protoplanetary disks, followed by examinations of detectable signals in synthetic CO emission line observations at millimeter wavelengths. We advocate for using residual velocity or channel maps, generated by subtracting an azimuthally averaged background of the disk, to identify planet-induced kinematic perturbations. We investigate the effects of two basic simulation parameters, simulation duration and numerical resolution, on the simulation results. Our findings suggest that a short simulation (e.g., 100 orbits) is insufficient to establish a steady velocity pattern given our chosen viscosity ($\alpha=10^{-3}$), and displays plenty of fluctuations on orbital timescale. Such transient features could be detected in observations. By contrast, a long simulation (e.g., 1,000 orbits) is required to reach steady state in kinematic structures. At 1,000 orbits, the strongest and detectable velocity structures are found in the spiral wakes close to the planet. Through numerical convergence tests, we find hydrodynamics results converge in spiral regions at a resolution of 14 cells per disk scale height (CPH) or higher. Meanwhile, synthetic observations produced from hydrodynamic simulations at different resolutions are indistinguishable with 0.1$^{\prime\prime}$ angular resolution and 10 hours of integration time on ALMA., Comment: Accepted for publication in APJ, 18 pages, 16 figures

We introduce Disk2Planet, a machine learning-based tool to infer key parameters in disk-planet systems from observed protoplanetary disk structures. Disk2Planet takes as input the disk structures in the form of two-dimensional density and velocity maps, and outputs disk and planet properties, that is, the Shakura--Sunyaev viscosity, the disk aspect ratio, the planet--star mass ratio, and the planet's radius and azimuth. We integrate the Covariance Matrix Adaptation Evolution Strategy (CMA--ES), an evolutionary algorithm tailored for complex optimization problems, and the Protoplanetary Disk Operator Network (PPDONet), a neural network designed to predict solutions of disk--planet interactions. Our tool is fully automated and can retrieve parameters in one system in three minutes on an Nvidia A100 graphics processing unit. We empirically demonstrate that our tool achieves percent-level or higher accuracy, and is able to handle missing data and unknown levels of noise., Comment: Accepted to ApJ

The canonical theory for planet formation in circumstellar disks proposes that planets are grown from initially much smaller seeds. The long-considered alternative theory proposes that giant protoplanets can be formed directly from collapsing fragments of vast spiral arms induced by gravitational instability -- if the disk is gravitationally unstable. For this to be possible, the disk must be massive compared to the central star: a disk-to-star mass ratio of 1/10 is widely held as the rough threshold for triggering gravitational instability, inciting significant non-Keplerian dynamics and generating prominent spiral arms. While estimating disk masses has historically been challenging, the motion of the gas can reveal the presence of gravitational instability through its effect on the disk velocity structure. Here we present kinematic evidence of gravitational instability in the disk around AB Aurigae, using deep observations of 13CO and C18O line emission with the Atacama Large Millimeter/submillimeter Array (ALMA). The observed kinematic signals strongly resemble predictions from simulations and analytic modelling. From quantitative comparisons, we infer a disk mass of up to 1/3 the stellar mass enclosed within 1" to 5" on the sky., Comment: Published in Nature. 4 main figures, 9 extended data figures, 1 extended data table. Published version at https://www.nature.com/articles/s41586-024-07877-0. Observational data products available at https://doi.org/10.11570/24.0087 with reduction guide & scripts at https://jjspeedie.github.io/guide.2021.1.00690.S. Simulated data products available at https://doi.org/10.5281/zenodo.11668694

The PDS 70 system, hosting two planets within its disk, is an ideal target for examining the effect of planets on dust accumulation, growth, and ongoing planet formation. Here, we present high-resolution ($0.''07 = 8 \ \mathrm{au}$) dust continuum observations of the PDS 70 disk in ALMA Band 3 (3.0 mm). While previous Band 7 observations showed a dust ring with slight asymmetry, our Band 3 observations reveal a more prominent asymmetric peak in the northwest direction, where the intensity is 2.5 times higher than in other directions and the spectral index is at the local minimum with $\alpha_{\mathrm{SED}} \sim 2.2$. This indicates that a substantial amount of dust is accumulated both radially and azimuthally in the peak. We also detect point-source emission around the stellar position in the Band 3 image, which is likely to be free-free emission. We constrain the eccentricity of the outer ring to be $e<0.04$ from the position of the central star and the outer ring. From the comparison with numerical simulations, we constrain the mass of PDS 70c to be less than 4.9 Jupiter masses if the gas turbulence strength $\alpha_{\mathrm{turb}} = 10^{-3}$. Then, we discuss the formation mechanism of the disk structures and further planet formation scenarios in the disk., Comment: accepted to ApJL

PDS~70 is a protoplanetary system that hosts two actively accreting gas giants, namely PDS~70b and PDS~70c. The system has a $\sim$60--100 au dusty ring that has been resolved by ALMA, along with circumplanetary disks around the two gas giants. Here we report the first JVLA Q (40--48 GHz), Ka (29--37 GHz), K (18--26 GHz), and X (8--12 GHz) bands continuum observations, and the complementary ALMA Bands 3 ($\sim$98 GHz) and 4 ($\sim$145 GHz) observations towards PDS~70. The dusty ring appears azimuthally asymmetric in our ALMA images. We obtained firm detections at Ka and K bands without spatially resolving the source; we obtained a marginal detection at Q band, and no detection at X band. The spectral indices ($\alpha$) are 5$\pm$1 at 33--44 GHz and 0.6$\pm$0.2 at 22--33 GHz. At 10--22 GHz, the conservative lower limit of $\alpha$ is 1.7. The 33--44 GHz flux density is likely dominated by the optically thin thermal emission of grown dust with $\gtrsim$1 mm maximum grain sizes, which may be associated with the azimuthally asymmetric substructure induced by planet-disk interaction. Since PDS~70 was not detected at X band, we found it hard to explain the low spectral index at 22--33 GHz only with free-free emission. Hence, we attribute the dominant emission at 22--33 GHz to the emission of spinning nanometer-sized dust particles, while free-free emission may partly contribute to emission at this frequency range. In some protoplanetary disks, the emission of spinning nanometer-sized dust particles may resemble the 20--50 GHz excess in the spectra of millimeter-sized dust. The finding of strong continuum emission of spinning nanometer-sized particles can complicate the procedure of constraining the properties of grown dust. Future high-resolution, multi-frequency JVLA/ngVLA and SKA observations may shed light on this issue.

Recent observations have confirmed circumplanetary disks (CPDs) embedded in parental protoplanetary disks (PPDs). On the other hand, planetary-mass companions (PMCs) and planetary-mass objects (PMOs) are likely to harbor their own accretion disks. Unlike PPDs, CPDs and other disks around planet analogues are generally too compact to be spatially resolved by current instrumentation. In this study, we generate over 4,000 spectral energy distributions (SEDs) of circum-PMO-disks (CPMODs) with various host temperature and disk properties, which can be categorized into four prototypes, i.e., full, pre-transitional, transitional and evolved CPMODs. We propose a classification scheme based on their near-to-mid-infrared colors. Using those CPMOD models, we synthesize JWST (NIRCam and MIRI) photometry for F444W, F1000W and F2550W wide filters. We show F444W - F1000W and F444 - F2550W colors can be applied to distinguish different types of CPMODs, especially for those around hot hosts. Our results indicate that the ongoing and future JWST observations are promising to unveil structures and properties of CPMODs., Comment: 18 pages, 7 figures, accepted for publication in ApJ

We observed the planet-hosting system PDS 70 with the James Webb Interferometer, JWST's Aperture Masking Interferometric (AMI) mode within NIRISS. Observing with the F480M filter centered at 4.8 $\mu$m, we simultaneously fit a geometric model to the outer disk and the two known planetary companions. We re-detect the protoplanets PDS 70 b and c at an SNR of 21 and 11, respectively. Our photometry of both PDS 70 b and c provide evidence for circumplanetary disk emission through fitting SED models to these new measurements and those found in the literature. We also newly detect emission within the disk gap at an SNR of $\sim$4, at a position angle of $207^{+11}_{-10}$ degrees, and an unconstrained separation within $\sim$200 mas. Follow-up observations will be needed to determine the nature of this emission. We place a 5$\sigma$ upper limit of $\Delta$mag = 7.56 on the contrast of the candidate PDS 70 d at 4.8 $\mu$m, which indicates that if the previously observed emission at shorter wavelengths is due to a planet, this putative planet has a different atmospheric composition than PDS 70 b or c. Finally, we place upper limits on emission from any additional planets in the disk gap. We find an azimuthally averaged 5$\sigma$ upper limit of $\Delta$mag $\approx$ 7.5 at separations greater than 125 mas. These are the deepest limits to date within $\sim$250 mas at 4.8 $\mu$m and the first space-based interferometric observations of this system., Comment: Submitted to ApJ

As part of the James Webb Space Telescope (JWST) Guaranteed Time Observation (GTO) program "Direct Imaging of YSOs" (program ID 1179), we use JWST NIRCam's direct imaging mode in F187N, F200W, F405N, and F410M to perform high contrast observations of the circumstellar structures surrounding the protostar HL Tau. The data reveal the known stellar envelope, outflow cavity, and streamers, but do not detect any companion candidates. We detect scattered light from an in-flowing spiral streamer previously detected in $\textrm{HCO}^+$ by ALMA, and part of the structure connected to the c-shaped outflow cavity. For detection limits in planet mass we use BEX evolutionary tracks when $M_\textrm{p}<2M_\textrm{J}$ and AMES-COND evolutionary tracks otherwise, assuming a planet age of 1 Myr (youngest available age). Inside the disk region, due to extended envelope emission, our point-source sensitivities are $\sim5$ mJy ($37~M_{\rm J}$) at 40 AU in F187N, and $\sim0.37$ mJy ($5.2~M_{\rm J}$) at 140 AU in F405N. Outside the disk region, the deepest limits we can reach are $\sim0.01$ mJy ($0.75~M_{\rm J}$) at a projected separation of $\sim525$ AU., Comment: 13 pages, 6 figures, 2 tables, accepted to AAS Astronomical Journal

The previous, high angular resolution 225 GHz ($\sim$1.3 mm) continuum observations on the transitional disk DM Tau have resolved an outer ring at 20-120 au radii that is weakly azimuthally asymmetric. We aimed to examine dust growth and filtration in the outer ring. We performed the $\sim$0$''$.06 ($\sim$8.7 au) resolution Karl G. Jansky Very Large Array (JVLA) 40-48 GHz ($\sim$7 mm; Q band) continuum observations and the complementary observations at lower frequencies. In addition, we analyzed the archival JVLA observations that were taken since 2010. Intriguingly, the Q band image resolved the azimuthally highly asymmetric, knotty dust emission sources close to the inner edge of the outer ring. Fitting the 8-700 GHz spectral energy distribution (SED) with two dust components indicates that the maximum grain size in these knotty dust emission sources is likely $\gtrsim$300 $\mu$m while it is $\lesssim$50 $\mu$m in the rest of the ring. These results may be explained by trapping of inward migrating grown dust close to the ring inner edge. The exact mechanism for developing the azimuthal asymmetry has not yet been identified, which may be due to planet-disk interaction that might also be responsible for the creation of the dust cavity and pressure bump, or the fluid instabilities and vortex formation due to shear motions. Finally, we remark that the asymmetries in DM Tau are hard to diagnose from the $\gtrsim$225 GHz observations owing to a high optical depth at the ring. In other words, the apparent symmetric or asymmetric morphology of the transitional disks may be related to the optical depths of those disks at the observing frequency., Comment: 16 pages, 7 figures; accepted to A&A

MWC 758 is a young star hosting a spiral protoplanetary disk. The spirals are likely companion-driven, and two previously-identified candidate companions have been identified -- one at the end the Southern spiral arm at ~0.6 arcsec, and one interior to the gap at ~0.1 arcsec. With JWST/NIRCam, we provide new images of the disk and constraints on planets exterior to ~1". We detect the two-armed spiral disk, a known background star, and a spatially resolved background galaxy, but no clear companions. The candidates that have been reported are at separations that are not probed by our data with sensitivity sufficient to detect them -- nevertheless, these observations place new limits on companions down to ~2 Jupiter-masses at ~150 au and ~0.5 Jupiter masses at ~600 au. Owing to the unprecedented sensitivity of JWST and youth of the target, these are among the deepest mass-detection limits yet obtained through direct imaging observations, and provide new insights into the system's dynamical nature., Comment: Accepted for publication in AJ

An inner component misaligned from an outer component in a protoplanetary disk can result in the former casting shadows on the latter. We present a new instance of shadowing on the outer disk around a very low mass star, ZZ~Tau~IRS. Through the analysis of near-infrared (NIR) archival data at $\lambda=1.6$~$\mu$m acquired with the Wide Field Camera 3 on the Hubble Space Telescope, we identified brightness asymmetries in the top and bottom halves of the highly inclined outer disk, separated by a dark lane. The brighter sides in the top and bottom halves are on the opposite sides, which we attributed to shadows cast by a misaligned inner disk. Radiative transfer modeling of the system with a misaligned angle of 15~deg between the inner and outer disks well reproduced the observations. Additionally, we found an elevated brightness temperature of $^{12}$CO~(3-2) at $r\sim30$~au on the brighter side in NIR wavelengths in the top half disk, which can be explained by the shadowing effect too. While the origin of the misaligned inner disk remains unclear, future monitoring observations to search for temporal variations in brightness asymmetries will likely provide useful clues., Comment: 12 pages, 8 figures, accepted in AJ

The Gemini Planet Imager (GPI) has excelled in imaging debris disks in the near-infrared. The GPI Exoplanet Survey (GPIES) imaged twenty-four debris disks in polarized $H$-band light, while other programs observed half of these disks in polarized $J$- and/or $K1$-bands. Using these data, we present a uniform analysis of the morphology of each disk to find asymmetries suggestive of perturbations, particularly those due to planet-disk interactions. The multi-wavelength surface brightness, the disk color and geometry permit identification of any asymmetries such as warps or disk offsets from the central star. We find that nineteen of the disks in this sample exhibit asymmetries in surface brightness, disk color, disk geometry, or a combination of the three, suggesting that for this sample, perturbations, as seen in scattered light, are common. The relationship between these perturbations and potential planets in the system are discussed. We also explore correlations among stellar temperatures, ages, disk properties, and observed perturbations. We find significant trends between the vertical aspect ratio and the stellar temperature, disk radial extent, and the dust grain size distribution power-law, $q$. We also confirm a trend between the disk color and stellar effective temperature, where the disk becomes increasingly red/neutral with increasing temperature. Such results have important implications on the evolution of debris disk systems around stars of various spectral types., Comment: 46 pages, 20 figures, 6 tables, accepted for publication in ApJ

While there have been nearly two dozen of spiral arms detected from planet-forming disks in near-infrared scattered light, none of their substellar drivers have been confirmed. By observing spiral systems in at least two epochs spanning multiple years, and measuring the motion of the spirals, we can distinguish the cause of the spirals, and locate the orbits of the driving planets if they trigger the spirals. Upon a recent validation of this approach using the co-motion between a stellar companion and a spiral, we obtained a second epoch observation for the spiral system in the disk of V1247 Ori in the $H$-band polarized scattered light using VLT/SPHERE/IRDIS. Combining our observations with archival IRDIS data, we established a $4.8$ yr timeline to constrain the V1247 Ori spiral motion. We obtained a pattern speed of $0.40^{\circ} \pm 0.09^{\circ}$ yr$^{-1}$ for the north-east spiral. This corresponds to an orbital period of $900\pm200$ yr, and thus the semi-major axis of the hidden planetary driver is $118\pm19$ au for a 2.0 $\pm$ 0.1 M$_\odot$ central star. The location agrees with the gap in ALMA dust continuum observations, providing joint support for the existence of a companion driving the scattered-light spirals while carving a millimeter gap. With an angular separation of 0.29" $\pm$ 0.05", this hidden companion is an ideal target for JWST imaging., Comment: Accepted for publication in Astronomy and Astrophysics; 6 pages, 5 figures

Planets can excite density waves and open annular gas gaps in protoplanetary disks. The depth of gaps is influenced by the evolving angular momentum carried by density waves. While the impact of radiative cooling on the evolution of density waves has been studied, a quantitative correlation to connect gap depth with the cooling timescale is lacking. To address this gap in knowledge, we employ the grid-based code Athena++ to simulate disk-planet interactions, treating cooling as a thermal relaxation process. We establish quantitative dependences of steady-state gap depth (Eq. 36) and width (Eq. 41) on planetary mass, Shakura-Sunyaev viscosity, disk scale height, and thermal relaxation timescale $(\beta)$. We confirm previous results that gap opening is the weakest when thermal relaxation timescale is comparable to local dynamical timescale. Significant variations in gap depth, up to an order of magnitude, are found with different $\beta$. In terms of width, a gap is at its narrowest around $\beta=1$, approximately $10\%$ to $20\%$ narrower compared to the isothermal case. When $\beta\sim100$, it can be $\sim20\%$ wider, and higher viscosity enhances this effect. We derive possible masses of the gas gap-opening planets in AS 209, HD 163296, MWC 480, and HL Tau, accounting for the uncertainties in local thermal relaxation timescale., Comment: 19 pages, 16 figures, 4 tables, accepted for publication in ApJ

Observations reveal protoplanetary discs being perturbed by flyby candidates. We simulate a scenario where an unbound perturber, i.e., a flyby, undergoes an inclined grazing encounter, capturing material and forming a second-generation protoplanetary disc. We run $N$--body and three-dimensional hydrodynamical simulations of a parabolic flyby grazing a particle disc and a gas-rich protoplanetary disc, respectively. In both our $N$--body and hydrodynamic simulations, we find that the captured, second-generation disc forms at a tilt twice the initial flyby tilt. This relationship is robust to variations in the flyby's tilt, position angle, periastron, and mass. We extend this concept by also simulating the case where the flyby has a disc of material prior to the encounter but we do not find the same trend. An inclined disc with respect to the primary disc around a misaligned flyby is tilted by a few degrees, remaining close to its initial disc tilt. Therefore, if a disc is present around the flyby before the encounter, the disc may not tilt up to twice the perturber tilt depending on the balance between the angular momentum of the circumsecondary disc and captured particles. In the case where the perturber has no initial disc, analyzing the orientation of these second-generation discs can give information about the orbital properties of the flyby encounter., Comment: 17 pages, 15 figures, accepted to MNRAS

The planetary obliquity plays a significant role in determining physical properties of planetary surfaces and climate. As direct detection is constrained due to the present observation accuracy, kinetic theories are helpful to predict the evolution of the planetary obliquity. Here the coupling effect between the eccentric Kozai-Lidov (EKL) effect and the equilibrium tide is extensively investigated, the planetary obliquity performs to follow two kinds of secular evolution paths, based on the conservation of total angular momentum. The equilibrium timescale of the planetary obliquity $t_{\mathrm{eq}}$ varies along with $r_{t}$, which is defined as the initial timescale ratio of the tidal dissipation and secular perturbation. We numerically derive the linear relationship between $t_{\mathrm{eq}}$ and $r_{t}$ with the maximum likelihood method. The spin-axis orientation of S-type terrestrials orbiting M-dwarfs reverses over $90^\circ$ when $r_{t} > 100$, then enter the quasi-equilibrium state between $40^\circ$ and $60^\circ$, while the maximum obliquity can reach $130^\circ$ when $r_{t} > 10^4 $. Numerical simulations show that the maximum obliquity increases with the semi-major axis ratio $a_1$/$a_2$, but is not so sensitive to the eccentricity $e_2$. The likelihood of obliquity flip for S-type terrestrials in general systems with $a_2 < 45$ AU is closely related to $m_1$. The observed potential oblique S-type planets HD 42936 b, GJ 86 Ab and $\tau$ Boot Ab are explored to have a great possibility to be head-down over the secular evolution of spin., Comment: 18 pages, 12 figures, accepted for publication in ApJ

We examined the grain size in the dust ring encircling the 0.19~$M_\sun$ T Tauri star CIDA 1 using the Karl G. Jansky Very Large Array (JVLA) at multiple centimeter wavelengths, with a spatial resolution of 0$\farcs$2--0$\farcs$9. We detected distinct partial-ring structures at these wavelengths around CIDA~1. Based on spatial distributions and spectral indexes, we determined that these centimeter emissions originated from dust, rather than free-free or synchrotron emissions. To estimate the maximum grain size ($a_{\rm max}$) within the ring, we compared the observed spectral energy distribution (SED) with SEDs calculated for different $a_{\rm max}$ values using radiative transfer calculations. Our findings indicate an $a_{\rm max}$ value of approximately 2.5~cm in the ring, assuming the dust opacity can be approximated by the DSHARP models. These results suggest that grain growth took place within the CIDA~1 ring, potentially facilitating more efficient planet formation through pebble accretion scenarios involving centimeter-sized pebbles., Comment: 14 pages, 5 figures, accepted in AJ

Protoplanetary disks, the birthplaces of planets, commonly feature bright rings and dark gaps in both continuum and line emission maps. Accreting planets are interacting with the disk, not only through gravity, but also by changing the local irradiation and elemental abundances, which are essential ingredients for disk chemistry. We propose that giant planet accretion can leave chemical footprints in the gas local to the planet, which potentially leads to the spatial coincidence of molecular emissions with the planet in ALMA observation. Through 2D multi-fluid hydrodynamical simulations in Athena++ with built-in sublimation, we simulate the process of an accreting planet locally heating up its vicinity, opening a gas gap in the disk, and creating the conditions for C-photochemistry. An accreting planet located outside the methane snowline can render the surrounding gas hot enough to sublimate the C-rich organics off pebbles before they are accreted by the planet. This locally elevates the disk gas-phase C/O ratio, providing a potential explanation for the C$_2$H line-emission rings observed with ALMA. In particular, our findings provide an explanation for the MWC480 disk, where previous work has identified a statistically significant spatial coincidence of line-emission rings inside a continuum gap. Our findings present a novel view of linking the gas accretion of giant planets and their natal disks through the chemistry signals. This model demonstrates that giant planets can actively shape their forming chemical environment, moving beyond the traditional understanding of the direct mapping of primordial disk chemistry onto planets., Comment: 18 pages, 13 figures, Accepted for publication in A&A

Understanding the driving forces behind spiral arms in protoplanetary disks remains a challenge due to the faintness of young giant planets. MWC 758 hosts such a protoplanetary disk with a two-armed spiral pattern that is suggested to be driven by an external giant planet. We present new thermal infrared observations that are uniquely sensitive to redder (i.e., colder or more attenuated) planets than past observations at shorter wavelengths. We detect a giant protoplanet, MWC 758c, at a projected separation of ~100 au from the star. The spectrum of MWC 758c is distinct from the rest of the disk and consistent with emission from a planetary atmosphere with Teff = 500 +/- 100 K for a low level of extinction (AV<30), or a hotter object with a higher level of extinction. Both scenarios are commensurate with the predicted properties of the companion responsible for driving the spiral arms. MWC 758c provides evidence that spiral arms in protoplanetary disks can be caused by cold giant planets or by those whose optical emission is highly attenuated. MWC 758c stands out both as one of the youngest giant planets known, and also as one of the coldest and/or most attenuated. Furthermore, MWC 758c is among the first planets to be observed within a system hosting a protoplanetary disk., Comment: Published in Nature Astronomy

Radio and near-infrared observations have observed dozens of protoplanetary disks that host spiral arm features. Numerical simulations have shown that companions may excite spiral density waves in protoplanetary disks via companion-disk interaction. However, the lack of direct observational evidence for spiral-driving companions poses challenges to current theories of companion-disk interaction. Here we report multi-epoch observations of the binary system HD 100453 with the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) facility at the Very Large Telescope. By recovering the spiral features via robustly removing starlight contamination, we measure spiral motion across 4 yr to perform dynamical motion analyses. The spiral pattern motion is consistent with the orbital motion of the eccentric companion. With this first observational evidence of a companion driving a spiral arm among protoplanetary disks, we directly and dynamically confirm the long-standing theory on the origin of spiral features in protoplanetary disks. With the pattern motion of companion-driven spirals being independent of companion mass, here we establish a feasible way of searching for hidden spiral-arm-driving planets that are beyond the detection of existing ground-based high-contrast imagers., Comment: Accepted for publication in Astronomy and Astrophysics; 12 pages, 9 figures

We develop a tool, which we name Protoplanetary Disk Operator Network (PPDONet), that can predict the solution of disk-planet interactions in protoplanetary disks in real-time. We base our tool on Deep Operator Networks (DeepONets), a class of neural networks capable of learning non-linear operators to represent deterministic and stochastic differential equations. With PPDONet we map three scalar parameters in a disk-planet system -- the Shakura \& Sunyaev viscosity $\alpha$, the disk aspect ratio $h_\mathrm{0}$, and the planet-star mass ratio $q$ -- to steady-state solutions of the disk surface density, radial velocity, and azimuthal velocity. We demonstrate the accuracy of the PPDONet solutions using a comprehensive set of tests. Our tool is able to predict the outcome of disk-planet interaction for one system in less than a second on a laptop. A public implementation of PPDONet is available at \url{https://github.com/smao-astro/PPDONet}., Comment: 10 pages, 6 figures, 2 tables; ApJL accepted

The traditional paradigm of viscosity-dominated evolution of protoplanetary discs has been recently challenged by magnetized disc winds. However, distinguishing wind-driven and turbulence-driven accretion through observations has been difficult. In this study, we present a novel approach to identifying their separate contribution to angular momentum transport by studying the gap and ring morphology of planet-forming discs in the ALMA continuum. We model the gap-opening process of planets in discs with both viscous evolution and wind-driven accretion by 2D multi-fluid hydrodynamical simulations. Our results show that gap-opening planets in wind-driven accreting discs generate characteristic substructures that differ from those in purely viscous discs. Specifically, we demonstrate that discs, where wind-driven accretion dominates the production of substructures, exhibit significant asymmetries. Based on the diverse outputs of mock images in the ALMA continuum, we roughly divide the planet-induced features into four regimes (moderate-viscosity dominated, moderate-wind dominated, strong-wind dominated, inviscid). The classification of these regimes sets up a potential method to constrain the strength of magnetized disc wind and viscosity based on the observed gap and ring morphology. We discuss the asymmetry feature in our mock images and its potential manifestation in ALMA observations., Comment: 11 pages, 6 figures, accepted by MNRAS. Welcome any comments and suggestions!

Spiral arms are observed in numerous protoplanetary discs. These spiral arms can be excited by companions, either on bound or unbound orbits. We simulate a scenario where an unbound perturber, i.e. a flyby, excites spiral arms during a periastron passage. We run three-dimensional hydrodynamical simulations of a parabolic flyby encountering a gaseous protoplanetary disc. The perturber mass ranges from $10\, \rm M_J$ to $1\, \rm M_{\odot}$. The perturber excites a two-armed spiral structure, with a more prominent spiral feature for higher mass perturbers. The two arms evolve over time, eventually winding up, consistent with previous works. We focus on analysing the pattern speed and pitch angle of these spirals during the whole process. The initial pattern speed of the two arms are close to the angular velocity of the perturber at periastron, and then it decreases over time. The pitch angle also decreases over time as the spiral winds up. The spirals disappear after several local orbital times. An inclined prograde orbit flyby induces similar disc substructures as a coplanar flyby. A solar-mass flyby event causes increased eccentricity growth in the protoplanetary disc, leading to an eccentric disc structure which dampens over time. The spirals' morphology and the disc eccentricity can be used to search for potential unbound stars or planets around discs where a flyby is suspected. Future disc observations at high resolution and dedicated surveys will help to constrain the frequency of such stellar encounters in nearby star-forming regions., Comment: 17 pages, 18 figures, accepted to MNRAS

Crescent-like asymmetric dust structures discovered in protoplanetary disks indicate dust aggregations. Thus, the research on them helps us understand the planet formation process. Here we analyze the ALMA data of the protoplanetary disk around the T-Tauri star SR 21, which has asymmetric structures detected in previous sub-millimeter observations. Imaged at ALMA Band 6 (1.3 mm) with a spatial resolution of about 0.$\arcsec$04, the disk is found to consist of two rings and three asymmetric structures, with two of the asymmetric structures being in the same ring. Compared to the Band 6 image, the Band 3 (2.7 mm) image also shows the three asymmetric structures but with some clumps. The elongated asymmetric structures in the outer ring could be due to the interactions of a growing planet. By fitting the Band 3 and Band 6 dust continuum data, two branches of solutions of maximum dust size in the disk are suggested: one is larger than 1 mm, and the other is smaller than 300 $\mu m$. High-resolution continuum observations at longer wavelengths as well as polarization observations can help break the degeneracy. We also suggest that the prominent spiral previously identified in VLT/SPHERE observations to the south of the star at 0.$\arcsec$25 may be the scattered light counterpart of the Inner Arc, and the structure is a dust-trapping vortex in nature. The discovered features in SR 21 make it a good target for studying the evolution of asymmetric structures and planet formation., Comment: Accepted by The Astrophysical Journal

In this study, we reported the results of high-resolution (0.14 arcsec) Atacama Large Millimeter/submillimeter Array (ALMA) observations of the 225 GHz dust continuum and CO molecular emission lines from the transitional disk around SY Cha. Our high-resolution observations clearly revealed the inner cavity and the central point source for the first time. The radial profile of the ring can be approximated by a bright narrow ring superimposed on a fainter wide ring. Furthermore, we found that there is a weak azimuthal asymmetry in dust continuum emission. For gas emissions, we detected $\rm{}^{12}CO$(2$-$1), $\rm{}^{13}CO$(2$-$1) and $\rm{}C^{18}O$(2$-$1), from which we estimated the total gas mass of the disk to be $2.2\times10^{-4}M_\odot$, assuming a CO/H$_2$ ratio of $10^{-4}$. The observations showed that the gas is present inside the dust cavity. The analysis of the velocity structure of the $\rm{}^{12}CO$(2$-$1) emission line revealed that the velocity is distorted at the location of the dust inner disk, which may be owing to warping of the disk or radial gas flow within the cavity of the dust disk. High-resolution observations of SY Cha showed that this system is composed of a ring and a distorted inner disk, which may be common, as indicated by the survey of transitional disk systems at a resolution of $\sim$0.1~arcsec., Comment: 33 pages, 22 figures

Spiral density waves generated by an embedded planet are understood to cause ``kinks'' in observed velocity channel maps of CO surface emission, by perturbing the gas motion within the spiral arms. If velocity kinks are a reliable probe of embedded planets, we should expect to see the planet-driven spiral arms in other observational tracers. We test this prediction by searching the dust continuum for the midplane counterparts of the spirals responsible for all of the velocity kink planet candidates reported to date, whose orbits lie inside the dust continuum disk. We find no clear detection of any spiral structure in current continuum observations for 6 of the 10 velocity kink planet candidates in our sample (DoAr 25, GW Lup, Sz 129, HD 163296 #2, P94, and HD 143006), despite the high planet masses inferred from the kink amplitude. The remaining 4 cases include 3 clear detections of two-armed dust spirals (Elias 27, IM Lup and WaOph 6) wherein neither spiral arm aligns with a wake originating from reported planet location, suggesting that under the planetary-origin hypothesis, an accurate method for inferring the location of the planet in the midplane may need to encompass vertical effects. The 10th case, HD 97048, is inconclusive with current knowledge of the disk geometry., Comment: 5 figures, 13 pages. Accepted for publication in ApJ Letters. Supplementary material available at https://doi.org/10.6084/m9.figshare.21330426

The azimuthal asymmetries of dust rings in protoplanetary disks such as a crescent around young stars are often interpreted as dust traps, and thus as ideal locations for planetesimal and planet formations. Whether such dust traps effectively promote planetesimal formation in disks around very-low-mass stars (VLM; a mass of $\lesssim$0.2~$M_\odot$) is debatable, as the dynamical and grain growth timescales in such systems are long. To investigate grain growth in such systems, we studied the dust ring with crescent around the VLM star ZZ~Tau~IRS using the Karl G. Jansky Very Large Array (JVLA) at centimeter wavelengths. Significant signals were detected around ZZ~Tau~IRS. To estimate the maximum grain size ($a_{\rm max}$) in the crescent, we compared the observed spectral energy distribution (SED) with SEDs for various $a_{\rm max}$ values predicted by radiative transfer calculations. We found $a_{\rm max} \gtrsim$~1~mm and $\lesssim$~60~$\mu$m in the crescent and ring, respectively, though our modeling efforts rely on uncertain dust properties. Our results suggest that grain growth occurred in the ZZ~Tau~IRS disk, relative to sub-micron-sized interstellar medium. Planet formation in crescent with mm-sized pebbles might proceed more efficiently than in other regions with sub-millimeter-sized pebbles via pebble accretion scenarios., Comment: 11 pages, 3 figures, accepted in ApJ

As one of the most commonly observed disk substructures, dust rings from high-resolution disk surveys appear to have different radial widths. Recent observations on PDS 70 and AB Aur reveal not only planets in the disk, but also the accompanying wide dust rings. We use three-dimensional dust-and-gas disk simulations to study whether gap-opening planets are responsible for the large ring width in disk observations. We find that gap-opening planets can widen rings of dust trapped at the pressure bump via planetary perturbations, even with the mid-plane dust-to-gas ratio approaching order unity and with the dust back-reaction accounted for. We show that the planet-related widening effect of dust rings can be quantified using diffusion-advection theory, and provide a generalized criterion for an equilibrated dust ring width in three-dimensional disk models. We also suggest that the ring width can be estimated using the gas turbulent viscosity $\alpha_{\rm turb}$, but with cautions about the Schmidt number greater than order unity., Comment: 17 pages, 6+3 figures, 2 tables, accepted in ApJ

Scattered light imaging studies have detected nearly two dozen spiral arm systems in circumstellar disks, yet the formation mechanisms for most of them are still under debate. Although existing studies can use motion measurements to distinguish leading mechanisms such as planet-disk interaction and disk self-gravity, close-in stellar flybys can induce short-lived spirals and even excite arm-driving planets into highly eccentric orbits. With unprecedented stellar location and proper motion measurements from Gaia DR3, here we study for known spiral arm systems their flyby history with their stellar neighbours by formulating an analytical on-sky flyby framework. For stellar neighbors currently located within 10 pc from the spiral hosts, we restrict the flyby time to be within the past $10^4$ yr and the flyby distance to be within $10$ times the disk extent in scattered light. Among a total of $12570$ neighbors that are identified in Gaia DR3 for $20$ spiral systems, we do not identify credible flyby candidates for isolated systems. Our analysis suggests that close-in recent flyby is not the dominant formation mechanism for isolated spiral systems in scattered light., Comment: 14 pages, 4 figures, 2 tables, ApJS accepted. Data files for Table 2 in the ancillary folder. Code framework available at https://github.com/slinling/afm-spirals

Large inner dust gaps in transition disks are frequently posited as evidence of giant planets sculpting gas and dust in the disk, or the opening of a gap by photoevaporative winds. Although the former hypothesis is strongly supported by the observations of planets and deep depletions in gas within the gap some disks, many T Tauri stars hosting transition disks accrete at rates typical for an undepleted disk, raising the question of how gap opening occurs in these objects. We thus present an analysis of the structure of the transition disk around the T Tauri star DM Tau, which is strongly accreting ($\sim 10^{-8.3}~\mathrm{M}_\odot~ \mathrm{yr}^{-1}$) and turbulent ($\alpha=0.078 \pm 0.02$). Using the DALI thermochemical code, we fit disk models to simultaneously reproduce the accretion rate, high level of turbulence, the gas traced by ALMA band 6 observations of $^{12}$CO, $^{13}$CO, and C$^{18}$O J=2--1 lines, and the observed dust emission from the mm continuum and spectral energy distribution. We find a shallow depletion in gas surface density of $\sim 10$ relative to the outer disk and a gas rich inner disk is consistent with the observations. The planet mass of $<1$ M$_\mathrm{Jup}$ implied by the gap depth is in tension with predictions for dust trapping in a highly viscous disk, which requires a more massive planet of of $\sim10$M$_\mathrm{Jup}$. Photoevaporative models including a dead zone can qualitatively reproduce some features of the DM Tau disk, but still struggle to explain the high accretion rates and the observed mm continuum flux., Comment: Accepted for publication in the Astronomical Journal. 36 pages, 28 figures

The substructures observed in protoplanetary disks may be the signposts of embedded planets carving gaps or creating vortices. The inferred masses of these planets often fall in the Jovian regime despite their low abundance compared to lower-mass planets, partly because previous works often assume that a single substructure (a gap or vortex) is caused by a single planet. In this work, we study the possible imprints of compact systems composed of Neptune-like planets ($\sim10-30\;M_\oplus$) and show that long-standing vortices are a prevalent outcome when their inter-planetary separation ($\Delta a$) falls below $\sim8$ times $H_{{\rm p}}$ -- the average disk's scale height at the planets locations. In simulations where a single planet is unable to produce long-lived vortices, two-planet systems can preserve them for at least $5,000$ orbits in two regimes: i) fully-shared density gaps with elongated vortices around the stable Lagrange points $L_4$ and $L_5$ for the most compact planet pairs ($\Delta a \lesssim 4.6\; H_{{\rm p}}$); ii) partially-shared gaps for more widely spaced planets ($\Delta a \sim 4.6 - 8\;H_{{\rm p}}$) forming vortices in a density ring between the planets through the Rossby wave instability. The latter case can produce vortices with a wide range of aspect ratios down to $\sim3$ and can occur for planets captured into the 3:2 (2:1) mean-motion resonances for disk's aspects ratios of $h\gtrsim 0.033$ ($h\gtrsim 0.057$). We suggest that their long lifetimes are sustained by the interaction of spiral density waves launched by the neighboring planets. Overall, our results show that distinguishing imprint of compact systems with Neptune-mass planets are long-lived vortices inside the density gaps, which in turn are shallower than single-planet gaps for a fixed gap width., Comment: 17 pages, 7 figures, 1 table, submitted to The Astrophysical Journal

Sparse aperture masking interferometry (SAM) is a high resolution observing technique that allows for imaging at and beyond a telescope's diffraction limit. The technique is ideal for searching for stellar companions at small separations from their host star; however, previous analysis of SAM observations of young stars surrounded by dusty disks have had difficulties disentangling planet and extended disk emission. We analyse VLT/SPHERE-IRDIS SAM observations of the transition disk LkCa\,15, model the extended disk emission, probe for planets at small separations, and improve contrast limits for planets. We fit geometrical models directly to the interferometric observables and recover previously observed extended disk emission. We use dynamic nested sampling to estimate uncertainties on our model parameters and to calculate evidences to perform model comparison. We compare our extended disk emission models against point source models to robustly conclude that the system is dominated by extended emission within 50 au. We report detections of two previously observed asymmetric rings at $\sim$17 au and $\sim$45 au. The peak brightness location of each model ring is consistent with the previous observations. We also, for the first time with imaging, robustly recover an elliptical Gaussian inner disk, previously inferred via SED fitting. This inner disk has a FWHM of ~5 au and a similar inclination and orientation as the outer rings. Finally, we recover no clear evidence for candidate planets. By modelling the extended disk emission, we are able to place a lower limit on the near infrared companion contrast of at least 1000., Comment: Accepted for publication in ApJ

Direct images of protoplanets embedded in disks around infant stars provide the key to understanding the formation of gas giant planets like Jupiter. Using the Subaru Telescope and Hubble Space Telescope, we find evidence for a jovian protoplanet around AB Aurigae orbiting at a wide projected separation (93 au), likely responsible for multiple planet-induced features in the disk. Its emission is reproducible as reprocessed radiation from an embedded protoplanet. We also identify two structures located at 430-580 au that are candidate sites of planet formation. These data reveal planet formation in the embedded phase and a protoplanet discovery at wide, > 50 au separations characteristic of most imaged exoplanets. With at least one clump-like protoplanet and multiple spiral arms, the AB Aur system may also provide the evidence for a long-considered alternative to the canonical model for Jupiter's formation: disk (gravitational) instability., Comment: Author's personal version: 19 pages, 5 Figures, 1 Table; 32 Supplementary pages, 18 Supplementary Figures, 1 Supplementary Table; Accepted for Publication in Nature Astronomy. Published version: https://www.nature.com/articles/s41550-022-01634-x

Azimuthally asymmetric structures have been discovered in millimeter continuum emission from many protoplanetary disks. One hypothesis is that they are vortices produced by the Rossby wave instability, for example at edges of planet-opened gaps or deadzones. Confirming the vortex nature of these structures will have profound implications to planet formation. One way to test the hypothesis is to compare the observed morphology of vortex candidates in near-infrared scattered light with theoretical expectations. To this end, we synthesize the appearance of vortices in H-band polarized light by combining hydrodynamic and radiative transfer simulations of the Rossby wave instability at a deadzone edge. In a disk at 140 pc, at the peak in its evolution a vortex at 65 au may appear as a radially narrow arc 50% - 70% brighter compared with an axisymmetric disk model. The contrast depends on the inclination of the disk and the position angle of the vortex only weakly. Such contrast levels are well detectable in imaging observations of bright disks using instruments such as VLT/SPHERE, Subaru/SCExAO, and Gemini/GPI. A vortex also casts a shadow in the outer disk, which may aid its identification. Finally, at modest to high inclinations (e.g., 60 degrees) a vortex may mimic a one-armed spiral. In the HD 34282 disk, such a one-armed spiral with a shadowed region on the outside has been found in scattered light. This feature roughly coincides with an azimuthal asymmetry in mm continuum emission, signifying the presence of a vortex., Comment: 10 pages, 7 figures, ApJ accepted

Planet-disk interactions, where an embedded massive body interacts gravitationally with the protoplanetary disk it was formed in, can play an important role in reshaping both the disk and the orbit of the planet. Spiral density waves are launched into the disk by the planet, which, if they are strong enough, can lead to the formation of a gap. Both effects are observable with current instruments. The back-reaction of perturbations induced in the disk, both wave-like and non-wavelike, is a change in orbital elements of the planet. The efficiency of orbital migration is a long-standing problem in planet formation theory. We discuss recent progress in planet-disk interactions for different planet masses and disk parameters, in particular the level of turbulence, and progress in modeling observational signatures of embedded planets., Comment: 28 pages, 12 figures, chapter to appear in Protostars and Planets VII, eds. Shu-ichiro Inutsuka, Yuri Aikawa, Takayuki Muto, Kengo Tomida, and Motohide Tamura. Updated version including community input

ALMA continuum observations of thermal emission from the dust component of protoplanetary disks have revealed an abundance of substructures that may be interpreted as evidence for embedded planets, but planet-driven spiral arms -- perhaps one of the most compelling lines of evidence -- have proven comparatively elusive. In this work, we test the capabilities of ALMA to detect the planet-driven spiral signal in continuum emission. Carrying out hydrodynamic simulations and radiative transfer calculations, we present synthetic Band 7 continuum images for a wide range of disk and observing conditions. We show that thermal mass planets at tens of au typically drive spirals detectable within a few hours of integration time, and the detectable planet mass may be as low as $\sim$Neptune mass ($0.3 \, M_{\rm th}$). The grains probed by ALMA form spirals morphologically identical to the underlying gas spiral. The temperature of the dust spiral is crucial in determining its contrast, and spirals are easier to detect in disks with an adiabatic equation of state and longer cooling times. Resolving the spiral is not necessary for its detection; with the help of residual maps, the optimal beam size is a few times the spiral width at a constant noise level. Finally, we show how the presence of gaps and rings can impair our ability to recognize co-located spirals. Our work demonstrates the planet-finding potential of the current design specification of ALMA, and suggests that observing capability is not the bottleneck in searching for spirals induced by thermal mass planets., Comment: 11 figures, 20 pages. Accepted for publication in The Astrophysical Journal. Image repository available at https://doi.org/10.6084/m9.figshare.19148912

Close encounters between young stellar objects in star forming clusters are expected to dramatically perturb circumstellar disks. Such events are witnessed in numerical simulations of star formation, but few direct observations of ongoing encounters have been made. Here we report sub-0".1 resolution Atacama Large Millimeter Array (ALMA) and Jansky Very Large Array (JVLA) observations towards the million year old binary protostar Z CMa in dust continuum and molecular line emission. A point source ~4700 au from the binary has been discovered at both millimeter and centimeter wavelengths. It is located along the extension of a ~2000 au streamer structure previously found in scattered light imaging, whose counterpart in dust and gas emission is also newly identified. Comparison with simulations shows signposts of a rare flyby event in action. Z CMa is a "double burster", as both binary components undergo accretion outbursts, which may be facilitated by perturbations to the host disk by flybys., Comment: Published in Nature Astronomy. Here is the authors' version with the Supplementary Information integrated into the Methods section

Formed in protoplanetary disks around young stars, giant planets can leave observational features such as spirals and gaps in their natal disks through planet-disk interactions. Although such features can indicate the existence of giant planets, protoplanetary disk signals can overwhelm the innate luminosity of planets. Therefore, in order to image planets that are embedded in disks, it is necessary to remove the contamination from the disks to reveal the planets possibly hiding within their natal environments. We observe and directly model the detected disk in the Keck/NIRC2 vortex coronagraph $L'$-band observations of the single-armed protoplanetary disk around HD 34282. Despite a non-detection of companions for HD 34282, this direct disk modeling improves planet detection sensitivity by up to a factor of 2 in flux ratio and ${\sim}10 M_{\rm Jupiter}$ in mass. This suggests that performing disk modeling can improve directly imaged planet detection limits in systems with visible scattered light disks, and can help to better constrain the occurrence rates of self-luminous planets in these systems., Comment: 8 pages, 3 figures, 1 table, ApJ Letters accepted. Data files available in the ancillary folder

Polstar is a proposed NASA MIDEX mission that would feature a high resolution UV spectropolarimeter capable of measure all four Stokes parameters onboard a 60cm telescope. The mission would pioneer the field of time-domain UV spectropolarimetry. Time domain UV spectropolarimetry offers the best resource to determine the geometry and physical conditions of protoplanetary disks from the stellar surface to <5 AU. We detail two key objectives that a dedicated time domain UV spectropolarimetry survey, such as that enabled by Polstar, could achieve: 1) Test the hypothesis that magneto-accretion operating in young planet-forming disks around lower-mass stars transitions to boundary layer accretion in planet-forming disks around higher mass stars; and 2) Discriminate whether transient events in the innermost regions of planet-forming disks of intermediate mass stars are caused by inner disk mis-alignments or from stellar or disk emissions., Comment: 16 pages, 7 figures

CI Tau is a young (~2 Myr) T Tauri system with a substantial near-infrared excess in its SED, indicating that the protoplanetary disk extends very close to its star. This is seemingly at odds with the radial-velocity discovery of CI Tau b, a ~12 MJ planet at ~0.1 au, which would be expected to carve a wide, deep cavity in the innermost disk. To investigate this apparent contradiction, we run 2D hydrodynamics simulations to study the effect of the planet on the disk, then post-process the results with radiative transfer to obtain an SED. We find that at ~0.1 au, even such a massive companion has little impact on the near-infrared excess, a result that holds regardless of planetary eccentricity and dust size distribution. Conversely, the observed full-disk signature in CI Tau's SED is consistent with the existence of the hot super-Jupiter CI Tau b. As our simulations uncover, clear transition-disk signatures in SEDs are more likely to be signposts of nascent "warm" Jupiters, located at around 1 AU in the future habitable zones of their host stars., Comment: Accepted to ApJL. Comments and questions welcome. v2: fixed abstract to reflect accepted version

GW Ori is a hierarchical triple star system with a misaligned circumtriple protoplanetary disc. Recent ALMA observations have identified three dust rings with a prominent gap at $100\, \rm au$ and misalignments between each of the rings. A break in the gas disc may be driven either by the torque from the triple star system or a planet that is massive enough to carve a gap in the disc. Once the disc is broken, the rings nodally precess on different timescales and become misaligned. We investigate the origins of the dust rings by means of $N$-body integrations and 3-dimensional hydrodynamic simulations. We find that for observationally-motivated parameters of protoplanetary discs, the disc does not break due to the torque from the star system. We suggest that the presence of a massive planet (or planets) in the disc separates the inner and outer disc. We conclude that the disc breaking in GW Ori is likely caused by undetected planets -- the first planet(s) in a circumtriple orbit., Comment: 17 pages, 16 figures, accepted to MNRAS

We present a high-contrast imaging search for Pa$\beta$ line emission from protoplanets in the PDS~70 system with Keck/OSIRIS integral field spectroscopy. We applied the high-resolution spectral differential imaging technique to the OSIRIS $J$-band data but did not detect the Pa$\beta$ line at the level predicted using the parameters of \cite{Hashimoto2020}. This lack of Pa$\beta$ emission suggests the MUSE-based study may have overestimated the line width of H$\alpha$. We compared our Pa$\beta$ detection limits with the previous H$\alpha$ flux and H$\beta$ limits and estimated $A_{\rm V}$ to be $\sim0.9$ and 2.0 for PDS~70~b and c respectively. In particular, PDS~70~b's $A_{\rm V}$ is much smaller than implied by high-contrast near-infrared studies, which suggests the infrared-continuum photosphere and the hydrogen-emitting regions exist at different heights above the forming planet., Comment: 8pages, 5 figs, accepted for publication in AJ

It is likely that young protostellar disks undergo a self-gravitating phase. Such systems are characterized by the presence of a spiral pattern that can be either in a quasi-steady state or in a nonlinear unstable condition. This spiral wave affects both the gas dynamics and kinematics, resulting in deviations from the Keplerian rotation. Recently, a lot of attention has been devoted to kinematic studies of planet-forming environments, and we are now able to measure even small perturbations of velocity field ($\lesssim 1 \%$ of the Keplerian speed) thanks to high spatial and spectral resolution observations of protostellar disks. In this work, we investigate the kinematic signatures of gravitational instability: we perform an analytical study of the linear response of a self-gravitating disk to a spiral-like perturbation, focusing our attention on the velocity field perturbations. We show that unstable disks have clear kinematic imprints into the gas component across the entire disk extent, due to the GI spiral wave perturbation, resulting in deviations from Keplerian rotation. The shape of these signatures depends on several parameters, but they are significantly affected by the cooling factor: by detecting these features, we can put constraints on protoplanetary disk cooling., Comment: Accepted for publication in APJL, 13 pages, 4 figures

High-resolution imaging of protoplanetary disks has unveiled a rich diversity of spiral structure, some of which may arise from disk-planet interaction. Using 3D hydrodynamics with $\beta$-cooling to a vertically-stratified background, as well as radiative-transfer modeling, we investigate the temperature rise in planet-driven spirals. In rapidly cooling disks, the temperature rise is dominated by a contribution from stellar irradiation, 0.3-3% inside the planet radius but always <0.5% outside. When cooling time equals or exceeds dynamical time, however, this is overwhelmed by hydrodynamic PdV work, which introduces a 10-20% perturbation within a factor of 2 from the planet's orbital radius. We devise an empirical fit of the spiral amplitude $\Delta (T)$ to take into account both effects. Where cooling is slow, we find also that temperature perturbations from buoyancy spirals -- a strictly 3D, non-isothermal phenomenon -- become nearly as strong as those from Lindblad spirals, which are amenable to 2D and isothermal studies. Our findings may help explain observed thermal features in disks like TW Hydrae and CQ Tauri, and underscore that 3D effects have a qualitatively important effect on disk structure., Comment: Accepted to AJ. Comments and questions welcome

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 HD135344B disc revealed two rings in the thermal continuum stemming from ~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 2-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 12km baselines. Angular resolutions of 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 suggest that turbulence, or superposed velocity components, is particularly strong in the spirals. The 12CO(2-1) 3-D rotation curve points at stellocentric accretion at radii within the inner dust ring, with a radial velocity of up to ~6%+-0.5% Keplerian, which corresponds to an excessively large accretion rate of ~2E-6M_sun/yr if all of the CO layer follows the 12CO(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., Comment: accepted to MNRAS

We present Atacama Large Millimeter/submillimeter Array (ALMA) gas and dust observations at band 7 (339~GHz: 0.89~mm) of the protoplanetary disk around a very low mass star ZZ~Tau~IRS with a spatial resolution of 0\farcs25. The $^{12}$CO~$J=3\rightarrow2$ position--velocity diagram suggests a dynamical mass of ZZ~Tau~IRS of $\sim$0.1--0.3~$M_{\sun}$. The disk has a total flux density of 273.9 mJy, corresponding to an estimated mass of 24--50~$M_\oplus$ in dust. The dust emission map shows a ring at $r=$ 58~au and an azimuthal asymmetry at $r=$ \jh{45}~au with a position angle of 135\degr. The properties of the asymmetry, including radial width, aspect ratio, contrast, and contribution to the total flux, were found to be similar to the asymmetries around intermediate mass stars ($\sim$2~$M_{\sun}$) such as MWC~758 and IRS~48. This implies that the asymmetry in the ZZ~Tau~IRS disk shares a similar origin with others, despite the star being $\sim$10 times less massive. Our observations also suggest that the inner and outer parts of the disk may be misaligned. Overall, the ZZ~Tau~IRS disk shows evidence of giant planet formation at $\sim$10 au scale at a few Myr. If confirmed, it will challenge existing core accretion models, in which such planets have been predicted to be extremely hard to form around very low mass stars., Comment: 19 pages, 7 figures, accepted in AJ

Dust gaps and rings appear ubiquitous in bright protoplanetary disks. Disk-planet interaction with dust-trapping at the edges of planet-induced gaps is one plausible explanation. However, the sharpness of some observed dust rings indicate that sub-mm-sized dust grains have settled to a thin layer in some systems. We test whether or not such dust around gas gaps opened by planets can remain settled by performing three-dimensional, dust-plus-gas simulations of protoplanetary disks with an embedded planet. We find planets massive enough to open gas gaps stir small, sub-mm-sized dust grains to high disk elevations at the gap edges, where the dust scale-height can reach ~70% of the gas scale-height. We attribute this dust 'puff-up' to the planet-induced meridional gas flows previously identified by Fung & Chiang and others. We thus emphasize the importance of explicit 3D simulations to obtain the vertical distribution of sub-mm-sized grains around gas gaps opened by massive planets. We caution that the gas-gap-opening planet interpretation of well-defined dust rings is only self-consistent with large grains exceeding mm in size., Comment: 15 pages, 7+2 figures, accepted in ApJ

We report an analysis of the dust disk around DM~Tau, newly observed with the Atacama Large Millimeter/submillimeter Array (ALMA) at 1.3 mm. The ALMA observations with high sensitivity (8.4~$\mu$Jy/beam) and high angular resolution (35~mas, 5.1~au) detect two asymmetries on the ring at $r\sim$20~au. They could be two vortices in early evolution, the destruction of a large scale vortex, or double continuum emission peaks with different dust sizes. We also found millimeter emissions with $\sim$50~$\mu$Jy (a lower limit dust mass of 0.3~$M_{\rm Moon}$) inside the 3-au ring. To characterize these emissions, we modeled the spectral energy distribution (SED) of DM~Tau using a Monte Carlo radiative transfer code. We found that an additional ring at $r=$ 1~au could explain both the DM~Tau SED and the central point source. The disk midplane temperature at the 1-au ring calculated in our modeling is less than the typical water sublimation temperature of 150~K, prompting the possibility of forming small icy planets there., Comment: 26 pages, 17 figures

We present Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 observations of dust continuum emission of the disk around WW Cha. The dust continuum image shows a smooth disk structure with a faint (low-contrast) dust ring, extending from $\sim 40$ au to $\sim 70$ au, not accompanied by any gap. We constructed the simple model to fit the visibility of the observed data by using MCMC method and found that the bump (we call the ring without the gap the bump) has two peaks at $40$ au and $70$ au. The residual map between the model and observation indicates asymmetric structures at the center and the outer region of the disk. These asymmetric structures are also confirmed by model-independent analysis of the imaginary part of the visibility. The asymmetric structure at the outer region is consistent with a spiral observed by SPHERE. To constrain physical quantities of the disk (dust density and temperature), we carried out radiative transfer simulations. We found that the midplane temperature around the outer peak is close to the freezeout temperature of CO on water ice ($\sim 30$ K). The temperature around the inner peak is about $50$ K, which is close to the freezeout temperature of H$_2$S and also close to the sintering temperature of several species. We also discuss the size distribution of the dust grains using the spectral index map obtained within the Band 6 data., Comment: 24 pages, 25 figures, accepted for publication in The Astrophysical Journal

Spiral arms have been observed in more than a dozen protoplanetary disks, yet the origin of nearly all systems is under debate. Multi-epoch monitoring of spiral arm morphology offers a dynamical way in distinguishing two leading arm formation mechanisms: companion-driven, and gravitational instability induction, since these mechanisms predict distinct motion patterns. By analyzing multi-epoch J-band observations of the SAO 206462 system using the SPHERE instrument on the Very Large Telescope (VLT) in 2015 and 2016, we measure the pattern motion for its two prominent spiral arms in polarized light. On one hand, if both arms are comoving, they can be driven by a planet at $86_{-13}^{+18}$ au on a circular orbit, with gravitational instability motion ruled out. On the other hand, they can be driven by two planets at $120_{-30}^{+30}$ au and $49_{-5}^{+6}$ au, offering a tentative evidence (3.0$\sigma$) that the two spirals are moving independently. The independent arm motion is possibly supported by our analysis of a re-reduction of archival observations using the NICMOS instrument onboard the Hubble Space Telescope (HST) in 1998 and 2005, yet artifacts including shadows can manifest spurious arm motion in HST observations. We expect future re-observations to better constrain the motion mechanism for the SAO 206462 spiral arms., Comment: 9 pages, 4 figures, 1 table. Updated correct data files for SPHERE and NICMOS observations available in ancillary folder