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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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Protoplanetary disks with large inner dust cavities are thought to host massive planetary or substellar companions. These disks show asymmetries and rings in the millimeter continuum, caused by dust trapping in pressure bumps, and potentially vortices or horseshoes. The origin of the asymmetries and their diversity remains unclear. We present a comprehensive study of 16 disks for which the gas surface density profile has been constrained by CO isotopologue data. We compare the azimuthal extents of the dust continuum profiles with the local gas surface density in each disk, and find that the asymmetries correspond to higher Stokes numbers or low gas surface density. We discuss which asymmetric structures can be explained by a horseshoe, a vortex or spiral density waves. Second, we reassess the gas gap radii from the $^{13}$CO maps, which are about a factor 2 smaller than the dust ring radii, suggesting that companions in these disks are in the brown dwarf mass regime ($\sim 15-50 M_{\rm Jup}$) or in the Super-Jovian mass regime ($\sim 3-15 M_{\rm Jup}$) on eccentric orbits. This is consistent with the estimates from contrast curves on companion mass limits. These curves rule out (sub)stellar companions ($q>$0.05) for the majority of the sample at the gap location, but it remains possible at even smaller radii. Third, we find that spiral arms in scattered light images are primarily detected around high luminosity stars with disks with wide gaps, which can be understood by the dependence of the spiral arm pitch angle on disk temperature and companion mass., Comment: 36 pages, 16 figures. Accepted by the Astronomical Journal. Version 2 has fixed Figure 11 for which the subplots got mixed up

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of a protoplanetary disk around the T Tauri star Sz~84 and analyses of the structures of the inner cavity in the central region of the dust disk. Sz~84's spectral energy distribution (SED) has been known to exhibit negligible infrared excess at $\lambda \lesssim$10~$\mu$m due to the disk's cavity structure. Analyses of the observed visibilities of dust continuum at 1.3~mm and the SED indicate that the size of the cavity in the disk of large (millimeter size) dust grains is 8~au in radius and that in the disk of small (sub-micron size) dust grains is 60~au in radius. Furthermore, from the SED analyses, we estimate that the upper limit mass of small dust grains at $r<$60~au is less than $\sim$10$^{-3}$~$M_{\rm earth}$, which is $\lesssim$0.01~\% of the total (small~$+$~large) dust mass at $r<$60~au. These results suggest that large dust grains are dominant at $r<$60~au, implying that dust grains efficiently grow with less efficient fragmentation in this region, potentially due to weak turbulence and/or stickier dust grains. The balance of grain growth and dust fragmentation is an important factor for determining the size of large dust grains in protoplanetary disks, and thus Sz~84 could serve as a good testbed for investigations of grain growth in such disks., Comment: 22 pages, 11 figures

More than a dozen young stars host spiral arms in their surrounding protoplanetary disks. The excitation mechanisms of such arms are under debate. The two leading hypotheses -- companion-disk interaction and gravitational instability (GI) -- predict distinct motion for spirals. By imaging the MWC 758 spiral arm system at two epochs spanning ${\sim}5$ yr using the SPHERE instrument on the Very Large Telescope (VLT), we test the two hypotheses for the first time. We find that the pattern speeds of the spirals are not consistent with the GI origin. Our measurements further evince the existence of a faint "missing planet" driving the disk arms. The average spiral pattern speed is $0.\!^\circ22\pm0.\!^\circ03$ yr$^{-1}$, pointing to a driver at $172_{-14}^{+18}$ au around a $1.9$ $M_\odot$ central star if it is on a circular orbit. In addition, we witness time varying shadowing effects on a global scale that are likely originated from an inner disk., Comment: 9 pages, 3 figures, published in ApJ Letters. Data files and gif movie of Figure 1ab in ancillary folder

We report the results of a ${\sim}4$-year direct imaging survey of 104 stars to resolve and characterize circumstellar debris disks in scattered light as part of the Gemini Planet Imager Exoplanet Survey. We targeted nearby (${\lesssim}150$ pc), young (${\lesssim}500$ Myr) stars with high infrared excesses ($L_{\mathrm{IR}} / L_\star > 10^{-5}$), including 38 with previously resolved disks. Observations were made using the Gemini Planet Imager high-contrast integral field spectrograph in $H$-band (1.6 $\mu$m) coronagraphic polarimetry mode to measure both polarized and total intensities. We resolved 26 debris disks and three protoplanetary/transitional disks. Seven debris disks were resolved in scattered light for the first time, including newly presented HD 117214 and HD 156623, and we quantified basic morphologies of five of them using radiative transfer models. All of our detected debris disks but HD 156623 have dust-poor inner holes, and their scattered-light radii are generally larger than corresponding radii measured from resolved thermal emission and those inferred from spectral energy distributions. To assess sensitivity, we report contrasts and consider causes of non-detections. Detections were strongly correlated with high IR excess and high inclination, although polarimetry outperformed total intensity angular differential imaging for detecting low inclination disks (${\lesssim} 70 \deg$). Based on post-survey statistics, we improved upon our pre-survey target prioritization metric predicting polarimetric disk detectability. We also examined scattered-light disks in the contexts of gas, far-IR, and millimeter detections. Comparing $H$-band and ALMA fluxes for two disks revealed tentative evidence for differing grain properties. Finally, we found no preference for debris disks to be detected in scattered light if wide-separation substellar companions were present., Comment: arXiv resubmission with typographical corrections. Accepted for publication in AJ. 19 figures, 7 tables

Scattered light imaging has revealed nearly a dozen circumstellar disks around young Herbig Ae/Be stars$-$enabling studies of structures in the upper disk layers as potential signs of on-going planet formation. We present the first images of the disk around the variable Herbig Ae star PDS 201 (V* V351 Ori), and an analysis of the images and spectral energy distribution through 3D Monte-Carlo radiative transfer simulations and forward modelling. The disk is detected in three datasets with LBTI/LMIRCam at the LBT, including direct observations in the $Ks$ and $L'$ filters, and an $L'$ observation with the 360$^\circ$ vector apodizing phase plate coronagraph. The scattered light disk extends to a very large radius of $\sim$250 au, which places it among the largest of such disks. Exterior to the disk, we establish detection limits on substellar companions down to $\sim$5 M$_{Jup}$ at $\gtrsim$1.5" ($\gtrsim$500 au), assuming the Baraffe et al. (2015) models. The images show a radial gap extending to $\sim$0.4" ($\sim$140 au at a distance of 340 pc) that is also evident in the spectral energy distribution. The large gap is a possible signpost of multiple high-mass giant planets at orbital distances ($\sim$60-100 au) that are unusually massive and widely-separated compared to those of planet populations previously inferred from protoplanetary disk substructures., Comment: Accepted for publication in AJ

We present new $H$-band scattered light images of the HD 32297 edge-on debris disk obtained with the Gemini Planet Imager (GPI). The disk is detected in total and polarized intensity down to a projected angular separation of 0.15", or 20au. On the other hand, the large scale swept-back halo remains undetected, likely a consequence of its markedly blue color relative to the parent body belt. We analyze the curvature of the disk spine and estimate a radius of $\approx$100au for the parent body belt, smaller than past scattered light studies but consistent with thermal emission maps of the system. We employ three different flux-preserving post-processing methods to suppress the residual starlight and evaluate the surface brightness and polarization profile along the disk spine. Unlike past studies of the system, our high fidelity images reveal the disk to be highly symmetric and devoid of morphological and surface brightness perturbations. We find the dust scattering properties of the system to be consistent with those observed in other debris disks, with the exception of HR 4796. Finally, we find no direct evidence for the presence of a planetary-mass object in the system., Comment: Accepted for publication in the Astronomical Journal

GW Ori is a hierarchical triple system which has a rare circumtriple disk. We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of 1.3 mm dust continuum and 12CO J=2-1 molecular gas emission of the disk. For the first time, we identify three dust rings in the disk at ~46, 188, and 338 AU, with estimated dust mass of ~70-250 Earth masses, respectively. To our knowledge, the outer ring in GW Ori is the largest dust ring ever found in protoplanetary disks. We use visibility modelling of dust continuum to show that the disk has misaligned parts and the innermost dust ring is eccentric. The disk misalignment is also suggested by the CO kinematics modelling. We interpret these substructures as evidence of ongoing dynamical interactions between the triple stars and the circumtriple disk., Comment: 17 pages, 3+3 figures, 2 tables; accepted by ApJL on 2020-04-29

The high occurrence rates of spiral arms and large central clearings in protoplanetary disks, if interpreted as signposts of giant planets, indicate that gas giants form commonly as companions to young stars ($<$ few Myr) at orbital separations of 10--300\,au. However, attempts to directly image this giant planet population as companions to more mature stars ($> 10$\, Myr) have yielded few successes. This discrepancy could be explained if most giant planets form "cold start," i.e., by radiating away much of their formation energy as they assemble their mass, rendering them faint enough to elude detection at later times. In that case, giant planets should be bright at early times, during their accretion phase, and yet forming planets are detected only rarely through direct imaging techniques. Here we explore the possibility that the low detection rate of accreting planets is the result of episodic accretion through a circumplanetary disk. We also explore the possibility that the companion orbiting the Herbig Ae star HD~142527 may be a giant planet undergoing such an accretion outburst., Comment: 17 pages, 2 figures, accepted by ApJ

We analyzed the young (2.8-Myr-old) binary system FS Tau A using near-infrared (H-band) high-contrast polarimetry data from Subaru/HiCIAO and sub-millimeter CO (J=2-1) line emission data from ALMA. Both the near-infrared and sub-millimeter observations reveal several clear structures extending to $\sim$240 AU from the stars. Based on these observations at different wavelengths, we report the following discoveries. One arm-like structure detected in the near-infrared band initially extends from the south of the binary with a subsequent turn to the northeast, corresponding to two bar-like structures detected in ALMA observations with an LSRK velocity of 1.19-5.64 km/s. Another feature detected in the near-infrared band extends initially from the north of the binary, relating to an arm-like structure detected in ALMA observations with an LSRK velocity of 8.17-16.43 km/s. From their shapes and velocities, we suggest that these structures can mostly be explained by two streamers that connect the outer circumbinary disk and the central binary components. These discoveries will be helpful for understanding the evolution of streamers and circumstellar disks in young binary systems., Comment: 20 pages, 11 figures, accepted for publication in The Astrophysical Journal

The SR24 multi-star system hosts both circumprimary and circumsecondary disks, which are strongly misaligned from each other. The circumsecondary disk is circumbinary in nature. Interestingly, both disks are interacting, and they possibly rotate in opposite directions. To investigate the nature of this unique twin disk system, we present 0.''1 resolution near-infrared polarized intensity images of the circumstellar structures around SR24, obtained with HiCIAO mounted on the Subaru 8.2 m telescope. Both the circumprimary disk and the circumsecondary disk are resolved and have elongated features. While the position angle of the major axis and radius of the NIR polarization disk around SR24S are 55$^{\circ}$ and 137 au, respectively, those around SR24N are 110$^{\circ}$ and 34 au, respectively. With regard to overall morphology, the circumprimary disk around SR24S shows strong asymmetry, whereas the circumsecondary disk around SR24N shows relatively strong symmetry. Our NIR observations confirm the previous claim that the circumprimary and circumsecondary disks are misaligned from each other. Both the circumprimary and circumsecondary disks show similar structures in $^{12}$CO observations in terms of its size and elongation direction. This consistency is because both NIR and $^{12}$CO are tracing surface layers of the flared disks. As the radius of the polarization disk around SR24N is roughly consistent with the size of the outer Roche lobe, it is natural to interpret the polarization disk around SR24N as a circumbinary disk surrounding the SR24Nb-Nc system., Comment: 14 pages, 5 figures, accepted for publication in AJ

Star formation involves the flow of gas and dust within molecular clouds into protostars and young stellar objects (YSOs) due to gravity. Along the way, these flows are shaped significantly by many other mechanisms, including pressure, turbulent motions, magnetic fields, stellar feedback, jets, and angular momentum. How all these mechanisms interact nonlinearly with each other on various length scales leads to the formation and evolution of substructures within clouds, including filaments, clumps, cores, disks, outflows, the protostars/YSOs themselves, and planets. In this white paper, prepared for the 2020 Long Range Plan panel which will recommend Canada's future directions for astronomy, we describe the observational and theoretical leadership in the star formation field that Canada's vibrant community has demonstrated over the past decade. Drawing from this extensive background, we identify five key questions that must be addressed for further progress to be made in understanding star formation in the next decade. Addressing these questions will improve our understanding of the dynamics of the dense gas and the role of the magnetic field in star formation, the optical properties of the dust used to trace mass and magnetic fields, the sources of variability in star-forming objects on short timescales, and the physical processes that specifically promote the clustering of stars. We further highlight key facilities in which Canada should become involved to continue making progress in this field. Single-dish facilities we recommend include LSST, trans-atmospheric far-infrared telescopes like BLAST-TNG and SPICA, and ground-based telescopes like JCMT, GBT, and CCAT-p. Interferometric facilities we recommend include ALMA, ngVLA, and SKA1., Comment: 11 pages, a contributed white paper prepared for Canada's 2020 Long Range Plan decadal process

We present $L^\prime$-band Keck/NIRC2 imaging and $H$-band Subaru/AO188+HiCIAO polarimetric observations of CQ Tau disk with a new spiral arm. Apart from the spiral feature our observations could not detect any companion candidates. We traced the spiral feature from the $r^2$-scaled HiCIAO polarimetric intensity image and the fitted result is used for forward modeling to reproduce the ADI-reduced NIRC2 image. We estimated the original surface brightness after throughput correction in $L^\prime$-band to be $\sim126$ mJy/arcsec$^2$ at most. We suggest that the grain temperature of the spiral may be heated up to $\sim$200 K in order to explain both of the $H$- and $L^{\prime}$-bands results. The $H$-band emission at the location of the spiral originates from the scattering from the disk surface while both scattering and thermal emission may contribute to the $L^{\prime}$-band emission. If the central star is only the light source of scattered light, the spiral emission at $L^\prime$-band should be thermal emission. If an inner disk also acts as the light source, the scattered light and the thermal emission may equally contribute to the $L^\prime$-band spiral structure., Comment: accepted for publication in AJ

Tidal encounters in star clusters perturb discs around young protostars. In Cuello et al. (2019a, Paper I) we detailed the dynamical signatures of a stellar flyby in both gas and dust. Flybys produce warped discs, spirals with evolving pitch angles, increasing accretion rates, and disc truncation. Here we present the corresponding observational signatures of these features in optical/near-infrared scattered light and (sub-) millimeter continuum and CO line emission. Using representative prograde and retrograde encounters for direct comparison, we post-process hydrodynamical simulations with radiative transfer methods to generate a catalogue of multi-wavelength observations. This provides a reference to identify flybys in recent near-infrared and sub-millimetre observations (e.g., RW Aur, AS 205, HV Tau & DO Tau, FU Ori, V2775 Ori, and Z CMa)., Comment: 11 pages, 5 figures, accepted for publication in MNRAS

We present ALMA observations of 12CO, 13CO, and C18O J=2--1 lines and the 230 GHz continuum for the FU Ori-type object (FUor) V900 Mon (d~1.5 kpc), for which the accretion burst was triggered between 1953 and 2009. We identified CO emission associated with a molecular bipolar outflow extending up to a ~10^4 au scale and a rotating molecular envelope extending over >10^4 au. The interaction with the hot energetic FUor wind, which was observed using optical spectroscopy, appears limited to a region within ~400 au of the star. The envelope mass and the collimation of the extended CO outflow suggest that the progenitor of this FUor is a low-mass Class I young stellar object (YSO). These parameters for V900 Mon, another FUor, and a few FUor-like stars are consistent with the idea that FUor outbursts are associated with normal YSOs. The continuum emission is marginally resolved in our observations with a 0."2x0."15 (~300x225 au) beam, and a Gaussian model provides a deconvolved FWHM of ~90 au. The emission is presumably associated with a dusty circumstellar disk, plus a possible contribution from a wind or a wind cavity close to the star. The warm compact nature of the disk continuum emission could be explained with viscous heating of the disk, while gravitational fragmentation in the outer disk and/or a combination of grain growth and their inward drift may also contribute to its compact nature., Comment: 21 pages, 11 figures, accepted by ApJ

Theoretical studies suggest that a giant planet around the young star MWC 758 could be responsible for driving the spiral features in its circumstellar disk. Here, we present a deep imaging campaign with the Large Binocular Telescope with the primary goal of imaging the predicted planet. We present images of the disk in two epochs in the $L^{\prime}$ filter (3.8 $\mu m$) and a third epoch in the $M^{\prime}$ filter (4.8 $\mu m$). The two prominent spiral arms are detected in each observation, which constitute the first images of the disk at $M^\prime$, and the deepest yet in $L^\prime$ ($\Delta L^\prime=$12.1 exterior to the disk at 5$\sigma$ significance). We report the detection of a S/N$\sim$3.9 source near the end of the Sourthern arm, and, from the source's detection at a consistent position and brightness during multiple epochs, we establish a $\sim$90% confidence-level that the source is of astrophysical origin. We discuss the possibilities that this feature may be a) an unresolved disk feature, and b) a giant planet responsible for the spiral arms, with several arguments pointing in favor of the latter scenario. We present additional detection limits on companions exterior to the spiral arms, which suggest that a $\lesssim$4 M$_{Jup}$ planet exterior to the spiral arms could have escaped detection. Finally, we do not detect the companion candidate interior to the spiral arms reported recently by Reggiani et al. (2018), although forward modelling suggests that such a source would have likely been detected., Comment: 10 pages, 4 figures, accepted for publication in ApJ

Using the Atacama Large Millimeter/submillimeter Array (ALMA), we observed the young Herbig star HD 100546, host to a prominent disk with a deep, wide gap in the dust. The high-resolution 1.3 mm continuum observation reveals fine radial and azimuthal substructures in the form of a complex maze of ridges and trenches sculpting a dust ring. The $^{12}$CO(2-1) channel maps are modulated by wiggles or kinks that deviate from Keplerian kinematics particularly over the continuum ring, where deviations span 90$^\circ$ in azimuth, covering 5 km s$^{-1}$. The most pronounced wiggle resembles the imprint of an embedded massive planet of at least 5 M$_{\rm Jup}$ predicted from previous hydrodynamical simulations (Perez, Casassus, & Benitez-Llambay 2018). Such planet is expected to open a deep gap in both gas and dust density fields within a few orbital timescales, yet the kinematic wiggles lie near ridges in the continuum. The lesser strength of the wiggles in the $^{13}$CO and C$^{18}$O isotopologues show that the kinematic signature weakens at lower disk heights, and suggests qualitatively that it is due to vertical flows in the disk surface. Within the gap, the velocity field transitions from Keplerian to strongly non-Keplerian via a twist in position angle, suggesting the presence of another perturber and/or an inner warp. We also present VLT/SPHERE sparse aperture masking data which recovers scattered light emission from the gap's edges but shows no evidence for signal within the gap, discarding a stellar binary origin for its opening., Comment: 10 pages, 6 figures. Accepted for publication in ApJ Letters

Two studies utilizing sparse aperture masking (SAM) interferometry and $H_{\rm \alpha}$ differential imaging have reported multiple jovian companions around the young solar-mass star, LkCa 15 (LkCa 15 bcd): the first claimed direct detection of infant, newly-formed planets ("protoplanets"). We present new near-infrared direct imaging/spectroscopy from the SCExAO system coupled with the CHARIS integral field spectrograph and multi-epoch thermal infrared imaging from Keck/NIRC2 of LkCa 15 at high Strehl ratios. These data provide the first direct imaging look at the same wavelengths and in the same locations where previous studies identified the LkCa 15 protoplanets and thus offer the first decisive test of their existence. The data do not reveal these planets. Instead, we resolve extended emission tracing a dust disk with a brightness and location comparable to that claimed for LkCa 15 bcd. Forward-models attributing this signal to orbiting planets are inconsistent with the combined SCExAO/CHARIS and Keck/NIRC2 data. An inner disk provides a more compelling explanation for the SAM detections and perhaps also the claimed $H_{\alpha}$ detection of LkCa 15 b. We conclude that there is currently no clear, direct evidence for multiple protoplanets orbiting LkCa 15, although the system likely contains at least one unseen jovian companion. To identify jovian companions around LkCa 15 from future observations, the inner disk should be detected and its effect modeled, removed, and shown to be distinguishable from planets. Protoplanet candidates identified from similar systems should likewise be clearly distinguished from disk emission through modeling., Comment: 12 pages, 4 figures, 1 table; Astrophysical Journal Letters in press

We analyze the highest-resolution millimeter continuum and near-infrared (NIR) scattered-light images presented to date of the circumbinary disk orbiting V4046 Sgr, a ~20 Myr old actively accreting, close binary T Tauri star system located a mere 72.4 pc from Earth. We observed the disk with the Atacama Large Millimeter/submillimeter Array (ALMA) at 870-micron during Cycle 4, and we analyze these data in conjunction with archival NIR (H band) polarimetric images obtained with SPHERE/IRDIS on the ESO Very Large Telescope. At 0.3'' (20 au) resolution, the 870-micron image reveals a marginally resolved ring that peaks at ~32 au and has an extension of ~ 90 au. We infer a lower limit on dust mass of ~ 60.0 M_earth within the 870-micron ring, and confirm that the ring is well aligned with the larger-scale gaseous disk. A second, inner dust ring is also tentatively detected in the ALMA observations; its position appears coincident with the inner (~14 au radius) ring detected in scattered light. Using synthetic 870 micron and H-band images obtained from disk-planet interaction simulations, we attempt to constrain the mass of the putative planet orbiting at 20 au. Our trials suggest that a circumbinary Jovian-mass planet may be responsible for generating the dust ring and gap structures detected within the disk. We discuss the longevity of the gas-rich disk orbiting V4046 Sgr in the context of the binary nature of the system., Comment: 13 pages, 5 figures, Accepted

Resolved ALMA and VLA observations indicate the existence of two dust traps in the protoplanetary disc MWC 758. By means of 2D gas+dust hydrodynamical simulations post-processed with 3D dust radiative transfer calculations, we show that the spirals in scattered light, the eccentric, asymmetric ring and the crescent-shaped structure in the (sub)millimetre can all be caused by two giant planets: a 1.5-Jupiter mass planet at 35 au (inside the spirals) and a 5-Jupiter mass planet at 140 au (outside the spirals). The outer planet forms a dust-trapping vortex at the inner edge of its gap (at ~85 au), and the continuum emission of this dust trap reproduces the ALMA and VLA observations well. The outer planet triggers several spiral arms which are similar to those observed in polarised scattered light. The inner planet also forms a vortex at the outer edge of its gap (at ~50 au), but it decays faster than the vortex induced by the outer planet, as a result of the disc's turbulent viscosity. The vortex decay can explain the eccentric inner ring seen with ALMA as well as the low signal and larger azimuthal spread of this dust trap in VLA observations. Finding the thermal and kinematic signatures of both giant planets could verify the proposed scenario., Comment: 18 pages, 8 figures, accepted for publication in MNRAS

We investigate how the detectability of signatures of self-gravity in a protoplanetary disc depends on its temporal evolution. We run a one-dimensional model for secular timescales to follow the disc mass as a function of time. We then combine this with three-dimensional global hydrodynamics simulations that employ a hybrid radiative transfer method to approximate realistic heating and cooling. We simulate ALMA continuum observations of these systems, and find that structures induced by the gravitational instability (GI) are readily detectable when $q=M_\mathrm{disc}/M_*\gtrsim 0.25$ and $R_\mathrm{outer}\lesssim 100$ au. The high accretion rate generated by gravito-turbulence in such a massive disc drains its mass to below the detection threshold in $\sim10^4$ years, or approximately 1 % of the typical disc lifetime. Therefore, discs with spiral arms detected in ALMA dust observations, if generated by self-gravity, must either be still receiving infall to maintain a high $q$ value, or have just emerged from their natal envelope. Detection of substructure in systems with lower $q$ is possible, but would require a specialist integration with the most extended configuration over several days. This disfavours the possibility of GI-caused spiral structure in systems with $q<0.25$ being detected in relatively short integration times, such as those found in the DSHARP ALMA survey (Andrews et al. 2018; Huang et al. 2018). We find no temporal dependence of detectability on dynamical timescales, Comment: 13 pages, 6 figures

Protoplanets can produce structures in protoplanetary disks via gravitational disk-planet interactions. Once detected, such structures serve as signposts of planet formation. Here we investigate the kinematic signatures in disks produced by multi-Jupiter mass ($M_{\rm J}$) planets using 3D hydrodynamics and radiative transfer simulations. Such a planet opens a deep gap, and drives transonic vertical motions inside. Such motions include both a bulk motion of the entire half-disk column, and turbulence on scales comparable to and smaller than the scale height. They significantly broaden molecular lines from the gap, producing double-peaked line profiles at certain locations, and a kinematic velocity dispersion comparable to thermal after azimuthal averaging. The same planet does not drive fast vertical motions outside the gap, except at the inner spiral arms and the disk surface. Searching for line broadening induced by multi-$M_{\rm J}$ planets inside gaps requires an angular resolution comparable to the gap width, an assessment of the gap gas temperature to within a factor of 2, and a high sensitivity needed to detect line emission from the gap., Comment: 20 pages, 11 figures, 1 appendix, ApJ accepted

We present H-band polarized scattered light imagery and JHK high-contrast spectroscopy of the protoplanetary disk around HD 163296 observed with the HiCIAO and SCExAO/CHARIS instruments at Subaru Observatory. The polarimetric imagery resolve a broken ring structure surrounding HD 163296 that peaks at a distance along the major axis of 0.65 (66 AU) and extends out to 0.98 (100 AU) along the major axis. Our 2011 H-band data exhibit clear axisymmetry, with the NW- and SE- side of the disk exhibiting similar intensities. Our data are clearly different than 2016 epoch H-band observations from VLT/SPHERE that found a strong 2.7x asymmetry between the NW- and SE-side of the disk. Collectively, these results indicate the presence of time variable, non-azimuthally symmetric illumination of the outer disk. Based on our 3D-MCRT modeling of contemporaneous IR spectroscopic and H-band polarized intensity imagery of the system, we suggest that while the system could plausibly host an inclined inner disk component, such a component is unlikely to be responsible for producing the observed time-dependent azimuthal variations in the outer scattered light disk of the system. While our SCExAO/CHARIS data are sensitive enough to recover the planet candidate identified from NIRC2 in the thermal IR, we fail to detect an object with a corresponding JHK brightness estimated from the atmospheric models of Baraffe et al. 2003. This suggests that the candidate is either fainter in JHK bands than model predictions, possibly due to extinction from the disk or atmospheric dust/clouds, or that it is an artifact of the dataset/data processing. Our SCExAO/CHARIS data lower the IR mass limits for planets inferred at larger stellocentric separations; however, these ALMA-predicted protoplanet candidates are currently still consistent with direct imaging constraints., Comment: 19 pages, 13 figures, 2 tables

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the dust continuum emission at 1.3 mm and 12CO J=2-1 line emission of the transitional disk around DM Tau. DM Tau's disk is thought to possess a dust-free inner cavity inside a few au, from the absence of near-infrared excess on its spectral energy distribution (SED). Previous submillimeter observations were, however, unable to detect the cavity; instead, a dust ring ~20 au in radius was seen. The excellent angular resolution achieved in the new ALMA observations, 43 x 31 mas, allows discovery of a 4 au radius inner dust ring, confirming previous SED modeling results. This inner ring is symmetric in continuum emission, but asymmetric in 12CO emission. The known (outer) dust ring at ~20 au is recovered and shows azimuthal asymmetry with a strong-weak side contrast of ~1.3. The gap between these two rings is depleted by a factor of ~40 in dust emission relative to the outer ring. An extended outer dust disk is revealed, separated from the outer ring by another gap. The location of the inner ring is comparable to that of the main asteroid belt in the solar system. As a disk with a "proto-asteroid belt," the DM Tau system offers valuable clues to disk evolution and planet formation in the terrestrial planet forming region., Comment: 14 pages, 5 figures, 2 tables. Accepted for publication in ApJ Letter

ALMA has found multiple dust gaps and rings in a number of protoplanetary disks in continuum emission at millimeter wavelengths. The origin of such structures is in debate. Recently, we documented how one super-Earth planet can open multiple (up to five) dust gaps in a disk with low viscosity ($\alpha\lesssim10^{-4}$). In this paper, we examine how the positions, depths, and total number of gaps opened by one planet depend on input parameters, and apply our results to real systems. Gap locations (equivalently, spacings) are the easiest metric to use when making comparisons between theory and observations, as positions can be robustly measured. We fit the locations of gaps empirically as functions of planet mass and disk aspect ratio. We find that the locations of the double gaps in HL Tau and TW Hya, and of all three gaps in HD 163296, are consistent with being opened by a sub-Saturn mass planet. This scenario predicts the locations of other gaps in HL Tau and TW Hya, some of which appear consistent with current observations. We also show how the Rossby wave instability may develop at the edges of several gaps and result in multiple dusty vortices, all caused by one planet. A planet as low in mass as Mars may produce multiple dust gaps in the terrestrial planet forming region., Comment: 16 pages; ApJ accepted