Contributed Posters

Protoplanetary disk chemistry        

Chemical analysis of early-type stars with planets

Jose Alacoria (ICATE-CONICET)

Several studies in the literature study the chemical composition of sun-like FGK stars with and without planets, while early-type stars are comparatively poorly studied. In this work, we present some preliminary results of the chemical pattern found in a sample of early-type stars (mostly A spectral types) with and without planets. One of the aims of the present work consists of analyzing the possible relationship between the presence of planets and the refractory-poor lambda Bootis stars. We also want to test a hypothesis proposed in the literature, in which the winds from a near hot-Jupiter planet could produce the accretion of volatile elements on the atmosphere of these early-type stars.

Constraining gas disk structure in MY Lupi with submillimeter and UV models

Nicole Arulanantham (Space Telescope Science Institute)

Physical-chemical models generate detailed maps of carbon, nitrogen, oxygen, and hydrogen bearing molecules in protoplanetary disks. However, the vertical disk structure in these models is degenerate with the amount of UV flux reaching the gas. Flat, strongly irradiated disk models and flared, weakly irradiated systems produce similar molecular gas distributions, which makes it difficult to examine UV sensitive photochemical pathways in systems from which submillimeter gas emission has not been spatially resolved. We investigate whether ultraviolet emission lines from fluorescent molecular hydrogen can be used to break this degeneracy, by using the Dust and LInes (DALI) code to generate a grid of physical-chemical models based on the disk around MY Lupi. The 2-D distributions of vibrationally excited molecular hydrogen from each DALI model are then irradiated with LyA photons, which pump the gas into excited electronic states. The resulting fluorescent emission lines are compared directly to observed UV features in HST-COS spectra of MY Lupi, showing that the H2 lines are best fit by a flared disk model with strong FUV irradiation and a high gas mass. We conclude that emission lines from UV spectra can provide important constraints for physical-chemical models of gas disks.

Water and 13C17O lines, and multiple ring and gap structures of the protoplanetary disk around HD 163296 observed by ALMA

Shota Notsu (Star and Planet Formation Laboratory, RIKEN)

Observationally locating the position of the H2O snowline (e.g., Hayashi et al. 1981, 1985) in protoplanetary disks is crucial for understanding the dust evolution and planet formation processes, and the origin of water on the Earth. The velocity profiles of emission lines from disks are usually affected by Doppler shift due to Keplerian rotation. Therefore, the line profiles are sensitive to the radial distribution of the line-emitting regions. In our previous works (Notsu et al. 2016, ApJ, 827, 113; 2017, ApJ, 836, 118; 2018, ApJ, 855, 62), we calculated the chemical composition of the disks around a T Tauri star and a Herbig Ae star using chemical kinetics and various water line profiles. We found that the water lines with small Einstein A coefficients and relatively high upper state energies are dominated by emission from the hot midplane region inside the H2O snowline, and therefore through analyzing their line profiles the position of the H2O snowline can be located. Since the fluxes of these lines from Herbig Ae disks are larger than those from T Tauri disks, the possibility of a successful detection is expected to increase for a Herbig Ae disk. There are several best candidate water lines that trace the position of the H2O snowline within the coverage of ALMA. Recently, we got the upper limit fluxes of submillimeter ortho-H2(16)O 321 GHz, para-H2(18)O 322 GHz, and HDO 335 GHz lines from the disk around the Herbig Ae star HD 163296, using ALMA (Notsu et al. 2019, ApJ, 875, 96). These water lines are considered to be the candidate water lines to locate the position of the H2O snowline, based on our model calculations. We compared the upper limit fluxes with the values calculated by our model calculations with dust emission, and we constrained the line emitting region and the dust opacity from the observations. We also detected multiple ring and gap patterns in the 0.9 mm (ALMA Band 7) dust continuum emission with 15 au spatial resolution, whose positions are consistent with those indicated by other observations (e.g., Isella et al. 2018).  Future observations of the submillimeter water lines with longer observation time are required to clarify the position of the H2O snowline in the disk midplane. In addition, we also detected the rarest stable CO isotopologue, 13C17O, in a disk for the first time (Booth et al. 2019, ApJL, 882, L31). We compared our observation with the existing detections of other CO isotoplogues in the HD163296 disk. We found that this line is optically thin within the CO snowline and will be thus a robust tracer of the bulk disk CO gas mass. We showed that this disk will be 2-6 times more massive than previously estimates.

Chemical signatures of a warped protoplanetary

Alison Young (University of Leicester)

Circumstellar discs may become warped or broken into distinct planes if there is a stellar or planetary companion with an orbit that is misaligned with respect to the disc. There is mounting observational evidence for protoplanetary discs with misaligned inner discs and warps that may be caused by such interactions with a previously undetected companion, giving us a tantalising indication of possible planets forming there. Hydrodynamical and radiative transfer models indicate that the temperature varies azimuthally in warped discs due to the variable angle at which the disc surface faces the star and this impacts the disc chemistry. We perform chemical modelling based on a hydrodynamical model of a protoplanetary disc with an embedded planet orbiting at a 12 degree inclination to the disc. Even for this small misalignment, abundances of many species including CO and HCO$^+$ vary azimuthally and this effect results in detectable azimuthal variations in submillimetre line emission. Azimuthal variations in line emission may therefore indicate the presence of an unseen embedded companion. Nonaxisymmetric chemical abundances should be considered when interpreting molecular line maps of warped or shadowed protoplanetary discs.


Protoplanetary disk structure, evolution, and dispersal             

Is HL Tau Gravitationally Stable?

Alice Booth (Leiden University)

Gas-giant planets on greater than 10 au orbits are the current exoplanet population probed via ALMA. There is now indirect evidence in both dust and CO gas observations for multiple gas-giant planets embedded in disks (e.g., HD 163296). The two proposed mechanisms for giant planet formation are core accretion and gravitational instability. The latter is an attractive solution to explain some of the detected exoplanet systems and the growing evidence for the "fast" (< 1 Myr) formation of gas-giant planets in disks. However, this mechanism relies on the disk having a high mass - higher than gas-mass estimates from C18O observations are suggesting. As the gas is expected to carry 99% of the disk mass in the early stages of disk evolution a robust measurement of this is necessary. In this poster, I present ALMA observations of the rarest carbon monoxide isotopologue, 13C17O, in the HL Tau disk. This species provides a more robust determination of the gas mass and reveals that the C18O emission is optically thick and therefore of the gas mass of the HL Tau disk has been significantly underestimated. I then show what this new mass means for the gravitational stability of the system.

Protoplanetary disks in the Orion Nebula Cluster: FUV radiation effects

Javiera Díaz (Institute of Astrophysics)

Many stars are formed within stellar clusters, and for that reason, their disks evolve being affected by the radiation of neighbor stars. The study of cases like those, where the protoplanetary disk is not isolated and is embedded in regions with external factors that can change their chemical evolution, are important because they would constrain the protoplanetary disk evolution, and thus the planet formation. The aim of this research is to analyze the effects of external FUV radiation on disk chemistry. We present ALMA Band 6 observations of CO isotopologues, HCN, DCN, H2CO, C2H, and C3H2 at 0.12 angular resolution toward a survey of four protoplanetary disks located in the Orion Nebula Cluster, where the radiation field is dominated by the massive and young O-type star, θ¹ Ori. This analysis is possible because the sources are located at different distances from the star, receiving different amounts of FUV radiation, so we can quantify this effect. An additional feature of these disks is that the sources are still embedded in the parent molecular cloud, then the molecular line emission is more difficult to detect.

Estimate on dust scale height from continuum image of the HD 163296 protoplanetary disk

Kiyoaki Doi (National Astronomical Observatory of Japan)

We aim at estimating the dust scale height of protoplanetary disks from millimeter continuum observations. First, we present a general expression of intensity of a ring in a protoplanetary disk, and show that we can constrain the dust scale height by the azimuthal variation of the intensity. Then, we apply the presented methodology to the two distinct rings at 68 au and at 100 au of the protoplanetary disk around HD 163296. We constrain the dust scale height by comparing the DSHARP high-resolution millimeter dust continuum image with radiative transfer simulations using RADMC-3D. We find that hd/hg > 0.55 at the inner ring and hd/hg < 0.44 at the outer ring in the 2 σ error range, where hd is the dust scale height and hg is the gas scale height. This indicates that the dust is flared at the inner ring and settled at the outer ring. We further constrain the ratio of turbulence parameter α to gas-to-dust-coupling parameter St from the derived dust scale height; α/St > 0.48 at the inner ring, and α/St < 0.19 at the outer ring. This results show that the turbulence is stronger or the dust is smaller at the inner ring than at the outer ring.

Vertical Shear Instability and Photoevaporative Winds

Lizxandra Flores-Rivera (Max Planck Institute for Astronomy)

In recent years hydrodynamical (HD) models have become important to describe the gas kinematics in protoplanetary disks,  especially in combination with models of photoevaporation and/or magnetically driven winds. Our aim is to investigate how  vertical shear instability (VSI) could influence the thermally driven winds on the surface of protoplanetary disks.
In this first part of the project, we focus on diagnosing the conditions of the VSI at the highest numerical resolution ever recorded, and suggest at what resolution per scale height we obtain convergence. At the same time, we want to investigate the vertical extent of VSI activity. Finally, we determine the regions where extreme UV (EUV), far-UV (FUV), and X-ray photons are dominant in the disk.
We perform global HD simulations using the PLUTO code. We adopt a global isothermal accretion disk setup, 2.5D (2 dimensions, 3 components) which covers a radial domain from 0.5 to 5.0 and an approximately full meridional extension. Our simulation runs cover a resolution from 12 to 203 cells per scale height.
We determine  50 cells per scale height to be the lower limit to resolve the VSI. For higher resolutions, >50 cells per scale height, we observe the convergence for the saturation level of the kinetic energy.  We are also able to identify the growth of the ``body'' modes, with higher growth rate for higher resolution. Full energy saturation and a turbulent steady state is reached after 70 local orbits. We determine the location of the EUV heated region defined by $\Sigma_{r}$=10$^{19}$ cm$^{-2}$ to be at $H_\mathrm{R}\sim9.7$ and the FUV--X-ray  heated boundary layer defined by $\Sigma_{r}$=10$^{22}$ cm$^{-2}$ to be at $H_\mathrm{R}\sim6.2$, making it necessary to introduce   a hot atmosphere. For the first time we report the presence of small-scale  vortices in the $r-Z$ plane between the characteristic layers of large-scale vertical velocity motions. Such vortices could lead to dust concentration, promoting grain growth. Our results highlight the importance of combining photoevaporation processes in the future high-resolution studies of  turbulence and accretion processes in disks.

Models and observations of external disc photoevaporation

Thomas Haworth (Queen Mary University of London)

I will review recent theoretical and observational advances in our understanding of how the radiation of star cluster environments impacts protoplantary disc evolution.

Strength and geometry of the large-scale fossil magnetic field in the accretion disks

Sergey Khaibrakhmanov (Ural Federal University)

We investigate the large-scale fossil magnetic field in the accretion disks of young stars [1,2]. We elaborate an MHD modification of Shakura and Sunyaev’s model [3]. In addition to the equations of Shakura and Sunyaev, we solve the equations of thermal and collisional ionization taking into account main ionization and recombination mechanisms, as well as dust grain evaporation. Induction equation is solved taking into account Ohmic dissipation, magnetic ambipolar diffusion, the Hall effect, and magnetic buoyancy. Analytical solution and numerical simulations of the model equations show that the magnetic buoyancy prevents runaway generation of the toroidal magnetic field, and magnetic field has quasi-azimuthal geometry in the innermost region of the disk. Magnetic field has quasi-poloidal geometry inside the `dead’ zone due to Ohmic dissipation. Ambipolar diffusion operates in the outer part of the disk, and magnetic field is quasi-radial or -azimuthal depending on the ionization rate and recombinations efficiency in this region. The Hall effect influences magnetic field geometry near the boundaries of the `dead’ zone. In the case of classical T Tauri star, magnetic field strength is of 10-300 G near the inner edge of the disk, 0.01 G at typical radial distance r=3 au inside the `dead’ zone, and it approaches interstellar value near the outer edge of the disk. Magnetic plasma beta is not constant over the disk, ranging from 100-1000 at the inner edge to 10^4-^5 inside the `dead’ zone and 1-10 at the outer edge. We compare our results with contemporary observational data on the magnetic field in the protoplanetary disks and show that the model predictions agree with the observations. The work is supported by Russian Science Foundation (project 19-72-10012).

Effect of Wind-Driven Accretion on Planetary Migration

Carolin Kimmig (Institute for Theoretical Astrophysics, Heidelberg University)

Can wind-driven accretion modify planetary migration?Planetary migration plays an important role in planet formation models and statistics of observed exoplanets. So far, the theory of planetary migration has focused on the interaction of one or more planets with an inviscid or viscously evolving gaseous disk. Wind-driven accretion, however, additionally influences the gas evolution in a protoplanetary disk and might therefore have an impact on the orbital parameters of a planet within the disk.
In 2D hydrodynamic simulations, we establish a simplified model of wind-driven accretion in protoplanetary disks treating the wind not explicitly but as a torque on the gas caused by the wind. With this simplified model we investigate the main effects with different wind strengths in a qualitative way rather than quantitatively predicting the outcome. We find that for the co-orbital region, this wind-driven process always injects mass from the outer edge of the co-orbital region and removes mass from the inner edge, in contrast to the viscous evolution, where mass is injected or removed from the co-orbital region depending on the radial density gradients in the disk. As a consequence, the migration behavior can differ strongly, and can under certain conditions drive rapid type-III-like outward migration.

The Ca II lines as tracers of the magnetospheric accretion flows: the Chamaeleon I star-forming region

Marbely Micolta (Universidad de Los Andes) 

According to the prevailing model, the broad emission lines characteristic of low mass, accreting young stars (Classical T Tauri Stars, CTTS) are formed in magnetospheric accretion flows. Current models rely on empirical temperature structures and geometries. Modeling lines arising from a variety of elements in different ionization stages can help constrain the temperature structure and the geometry and provide better determinations of the accretion rates. Our goals are to model the Ca II in CTTS to understand their formation and, assuming that the magnetospheric model is valid, use them to refine it, in particular, to constrain the temperature and geometry. We followed the methods of Muzerolle et al. (2001) to calculate the Ca II H, K, and IR Triplet lines for an extensive grid of magnetospheric models and used X-shooter spectra of 21 CTTS stars from the Chamaeleon I region (Manara et al. 2016,2017) to test the predictions of the magnetospheric accretion model. We find agreement between model predictions inferred from different lines. Preliminary fitting to the observations suggests that stars with the higher mass accretion rates have smaller disk truncation radius. More refined modeling to a larger set of stars, currently underway, is required to confirm this tantalizing suggestion. 

The imprint of X-ray photoevaporation onto the orbital distribution of giant planets

Kristina Monsch (USM/LMU Munich)

Recent exoplanet surveys have highlighted the existence of an impressive diversity of planetary systems, raising the question of how systems similar to our own can form and develop. The key to explaining the diversity of planetary systems is in the understanding of the statistical trends that are emerging from the recent wealth of exoplanet data. One of these is the non-uniform distribution of the semi-major axes of gas giants. Giant planets are found to preferentially clump up at orbital radii of ~1-2 au and finding what determines this peak is of strong interest. It has recently been suggested that this distribution may be established during the time of planetary migration in the protoplanetary disc, being halted by X-ray driven photoevaporation (Ercolano & Rosotti, 2015). We have searched for signatures of this process by correlating the X-ray luminosity of host stars with the semi-major axis distribution of their giant planets. Our statistical analysis of the observational data confirms a prominent feature that is also predicted by simulations, further strengthening the conclusion that X-ray photoevaporation may be shaping the architecture of planetary systems.

Observing Disk Accretion in Action

Joan Najita (NSF's NOIRLab)

Physical processes that redistribute or remove angular momentum from protoplanetary disks can drive mass accretion onto the star and affect the outcome of planet formation. Despite ubiquitous evidence that disks accrete, the process(es) responsible remain unclear. Here we present new results that appear to show disk accretion in action via rapid inflow of molecular gas at the surface of a protoplanetary disk. High-resolution mid-infrared spectroscopy of the Class I source GV Tau N reveals a rich redshifted absorption spectrum of individual lines of acetylene, hydrogen cyanide, ammonia, and water. The properties of the absorption indicate that the flow carries a significant accretion rate, comparable to stellar accretion rates of active T Tauri stars. The results may provide evidence for supersonic “surface accretion flows,” which have been found in MHD simulations of magnetized disks.



Detection and characterization of young exoplanets and circumplanetary disks 

The Structure and Stability of Extended Circumplanetary Disks (or Exorings)

Jess Speedie (University of Victoria)

Large dips in the brightness for a number of stars have been observed, for which the tentative explanation is occultation of the star by a transiting circumplanetary disc or ring system. In order for the circumplanetary disk/rings to block the host star's light, the disk must be tilted out of the planet's orbital plane, which poses stability problems due to the radial extent of the disk required to explain the brightness dip durations. This work uses N-body integrations to study the structure and stability of circumplanetary disk/ring systems tilted out of the planet's orbital plane by the spinning planet's mass quadrupole. Simulating the disk as a collection of test particles with orbits initialized near the Laplace surface (equilibrium between tidal force from host star and force from planet's mass quadrupole), we find that many extended, inclined circumplanetary disks remain stable over the duration of the integrations (~3-16 Myr). Two dynamical resonances/instabilities excite the particle eccentricities and inclinations: the Lidov-Kozai effect which occurs in the disk's outer regions, and ivection resonance which occurs in the disk's inner regions. Our work places constraints on the maximum radial extent of inclined circumplanetary disk/ring systems, and shows that gaps present in circumplanetary disks do not necessarily imply the presence of exomoons.


Role and origin of protoplanetary disk substructures        

The observational impact of dust trapping in self-gravitating discs

James Cadman (University of Edinburgh) 

The gravitational instability (GI) may play an important role in the very early evolution of protoplanetary discs by providing a source of viscosity, generating conditions suitable for accelerated dust growth, and potentially forming giant gaseous protoplanets through the direct gravitational collapse of disc material. It is now possible to observe young discs with telescopes such as ALMA. However a self-gravitating phase is likely to be brief (t<10^5 yrs) as a disc will rapidly evolve toward a lower mass, gravitationally stable state, thus limiting our prospects of observing these systems. In this work we use Monte Carlo radiative transfer models to analyse how dust-trapping in the spiral regions of self-gravitating discs results in enhanced emission, and we place constraints on the disc properties required to drive spiral features detectable with ALMA. We also analyse the Elias 27, WaOph 6 and IM Lup disc observations from the DSHARP survey, and make predictions about the nature of the spiral substructure which has been observed.

The Ophiuchus DIsc Survey Employing ALMA (ODISEA)–III: the evolution of substructures in massive discs at 3-5 au resolution

Lucas Cieza (Universidad Diego Portales)

We present 1.3 mm continuum ALMA long-baseline observations at 3-5 au resolution of 10 of the brightest discs from the ODISEA project. We identify a total of 26 narrow rings and gaps distributed in 8 sources and 3 discs with small dust cavities (r < 10 au). We find that two discs around embedded protostars lack the clear gaps and rings that are ubiquitous in more evolved sources with Class II SEDs. Our sample includes 5 objects with previously known large dust cavities (r >20 au). Our long-baseline observations resulted in the largest sample of discs observed at 3-5 au resolution in any given star-forming region (15 objects when combined with Ophiuchus objects in the DSHARP Large Program) and allow for a demographic study of the brightest 5% of the discs in Ophiuchus (i.e. the most likely formation sites of giant planets in the cloud). We use this unique sample to propose an evolutionary sequence and discuss a scenario in which the substructures observed in massive protoplanetary discs are mainly the result of planet formation and dust evolution. If this scenario is correct, the detailed study of disc substructures might provide a window to investigate a population of planets that remains mostly undetectable by other techniques.

These results are presented in

Frankenstein: Brightness profile reconstruction at super-resolution

Jeff Jennings (University of Cambridge)  

Interferometric observations of the mm dust distribution in protoplanetary discs now show a ubiquity of annular gaps and rings, as well as a nontrivial occurrence rate of asymmetric substructures. The identification and accurate characterization of these features is critical to probing the physical processes responsible. This poster summarizes Frankenstein, an open source code that recovers the 1D brightness profile of a disc at super-resolution. The code uses a nonparametric, fast (<1 min) Gaussian process to directly fit the 1D visibility distribution, yielding an accurate match of the visibility amplitudes to longer baseline (typically by a factor of 2 - 5) than the Fourier equivalent of a CLEAN brightness profile. This yields a more accurate constraint on the widths and amplitudes of disc gaps and rings, and often an identification of substructures not seen in the source’s CLEAN image.

Planet gap opening across stellar masses

Giovanni Rosotti (Leiden University) 

Gaps and rings are now ubiquitously found by high-resolution ALMA observations and planets are commonly invoked as an explanation. In this contribution I discuss how the minimum planet mass needed to open a gap varies across different stellar host masses and distances from the star. Naively gap opening around low-mass stars should be possible for lower mass planets, giving us a look into the young, low-mass planet population. Using dusty hydrodynamical simulations, I find however the opposite behaviour, as a result of the fact that discs around low-mass stars are geometrically thicker: gap opening around low-mass stars can require more massive planets. Depending on the theoretical isochrone employed to predict the relationship between stellar mass and luminosity, the gap opening planet mass could also be independent of stellar mass, but in no case I find that gap opening becomes easier around low-mass stars. This would lead to the expectation of a lower incidence of such structures in lower mass stars, since exoplanet surveys show that low-mass stars have a lower fraction of giant planets. More generally, this study enables future imaging observations as a function of stellar mass to be interpreted using information on the mass versus luminosity relations of the observed samples.

On the diversity of asymmetries in gapped protoplanetary disks

Nienke van der Marel (University of Victoria)  

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 13CO 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 or in the Super-Jovian mass regime on eccentric orbits. This is consistent with the estimates from contrast curves on companion mass limits. These curves rule out (sub)stellar companions 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."


Planet formation in multiple systems                                            

A Tale of Two Transition Disks: ALMA long-baseline observations of ISO-Oph 2 reveal two closely packed non-axisymmetric rings and a ∼2 au cavity

Camilo González Ruilova (Universidad Diego Portales) 

ISO-Oph 2 is a wide-separation (240 au) binary system where the primary star harbors a massive(Mdust∼40 M⊕) ring-like disk with a dust cavity∼50 au in radius and the secondary hosts a muchlighter (Mdust∼0.8 M⊕) disk.  As part of the high-resolution follow-up of the “Ophiuchus Disk Sur-vey Employing ALMA” (ODISEA) project, we present 1.3 mm continuum and 12CO molecular line observations of the system at 0.′′02 (3 au) resolution.  We resolve the disk around the primary into two non-axisymmetric rings and find that the disk around the secondary is only∼7 au across and also hasa dust cavity (r∼2.2 au).  Based on the infrared flux ratio of the system and the M0 spectral type of the primary, we estimate the mass of the companion to be close to the brown dwarf limit.  Hence, we conclude that the ISO-Oph 2 system contains the largest and smallest cavities, the smallest measured disk size, and the resolved cavity around the lowest mass object (M?∼0.08 M) in Ophiuchus.  From the 12CO  data,  we  find  a  bridge  of  gas  connecting  both  disks.   While  the  morphology  of  the  rings around  the  primary  might  be  due  to  an  unseen  disturber  within  the  cavity,  we  speculate  that  the bridge might indicate an alternative scenario in which the secondary has recently flown by the primarystar causing the azimuthal asymmetries in its disk.  The ISO-Oph 2 system is therefore a remarkable laboratory to study disk evolution, planet formation, and companion-disk interactions.

Measuring protoplanetary disk alignment in young binary systems

Eric Jensen (Swarthmore College)

Many of the known planetary systems are unlike our Solar System, containing hot Jupiters or planets orbiting their host stars on eccentric or inclined orbits. One possible explanation for producing such orbits is migration driven by Kozai-Lidov oscillations, which can be induced by a companion on a sufficiently inclined orbit. Observations of protoplanetary disks can help determine whether young binary companions are inclined relative to the individual stars’ nascent planetary systems and thus could induce such migration. We used ALMA to observe continuum and CO(3-2) emission from a sample of young binary systems in Taurus-Auriga, Ophiuchus, and Lupus. The kinematics of the CO emission allows us to deduce the spatial orientation of the disks, even for disks that are near our resolution limit. Comparing the orientations of the two disks within a given binary, we find examples of both well-aligned and significantly misaligned systems. Overall, our sample shows more tendency toward alignment than would be expected from a random distribution of disk inclinations, suggesting that binary formation favors aligned systems and/or that evolution toward relative alignment has occurred within 1-2 Myr of formation.

Dust rings formation in misaligned circumbinary discs "In many cases the result of molecular cloud collapse is a binary (or multiple) stellar system

Cristiano Longarini (Università degli Studi di Milano)

In particular, if the collapse is forming a binary system, three discs can be formed: two around the stars (circumprimary and circumsecundary) and a larger disc surrounding both the stars, called circumbinary. Here I present an analytical and numerical study of dust rings formation in misaligned circumbinary discs. In my work, I found that pile-ups of dust may be induced not only by pressure maxima, as the usual dust traps, but also by a difference in precession rates between the gas and dust. I considered a disc composed of gas and dust; I assumed that the gas precesses as a rigid body, thanks to the viscosity, while the dust differentially precesses because of its viscousless and pressureless nature. The net effect of the aerodynamical coupling between the two components is the so called “radial drift”, i.e. the dust acquires a negative radial velocity and migrate towards the central object. This force does not act whenever the difference of speed is equal to zero. Projecting the dusty velocity field onto the gaseous plane I found two radii - an inner and outer dust radius- at which the difference of speed between gas and dust is zero. At these locations, the dust, that is migrating from the outer part of the disc because of radial drift, piles up, leading to the formation of dusty rings. The position of the rings depends on a series of parameters defining the disc, as its radial extent, its density profile and its thickness. To confirm my theoretical predictions, I performed numerical simulations using the SPH code PHANTOM: I used the two fluid algorithm because I was interested in the marginally coupled regime. By means of these simulations I explored the parameter space as much as possible: I found an overall general agreement between the results of the simulations and the analytical expectations, with some discrepancies that can be related to the specific hypothesis I have made. This mechanism could be significant in the context of planetary formation in binary stellar systems because these traps could foster the dust coagulation and the formation of planetesimals."

On dust evolution in planet-forming discs in binary systems 

Francesco Zagaria (Institute of Astronomy, University of Cambridge, Uk) 

The  vast  majority  of  stars  are  in  binaries  or  higher-order  multiple  stellar  systems. Although  in  recent years  a  large  number  of  binaries  have  been  proven  to  host  exoplanets,  how  planet  formation  proceeds  in multiple stellar systems has not been studied yet with the necessary insight from the theoretical standpoint. Our aim is to fill this gap, focusing on the evolution of the dust grains in planet-forming discs in binaries. We take into account the dynamics of the gas and the dust in discs around each component of a binary system under the hypothesis that the evolution of the circumprimary and the circumsecondary discs is independent. It is known from previous theoretical and numerical studies that the secular evolution of the gas in binary discs is hastened due to the tidal interactions with their hosting stars. Here we prove that binarity affectsdust dynamics too, possibly in a more dramatic way than in the case of the gas. In particular, the presence of a stellar companion significantly reduces the amount of grains retained in binary discs because of a faster,more efficient radial drift, ultimately  shortening their lifetime. We prove that how rapidly discs  disperse depends both on the binary separation, with discs in wider binaries living longer, and on the disc viscosity. Although the less-viscous discs lose high amounts of solids in the earliest stages of their evolution, they are dissipated slowly, while those with higher viscosities show an opposite behaviour. The faster radial migration of solids in binary discs has a striking impact on planet formation, which seems to be inhibited in this hostile environment, unless other disc substructures halt radial drift further in. We conclude that planet formation in multiple stellar systems is likely to take place on very short time scales. As a post-processing step, we compute disc dust sizes from our models at ALMA wavelengths and compare them with the results of the multiple stellar disc surveys in Taurus and ρ Ophiuchus. We show that radial drift naturally explains the observed disc dust sizes without invoking very high eccentricities as previously assumed.


Dust evolution and planetesimal formation                                  

The Dust Properties and Origin of Substructures in HL Tau

Carlos Carrasco-González (Instituto de Radiastronomía y Astrofísica (IRyA-UNAM))

In 2014, one ALMA image of the dust emission in the HL Tau disk change forever our vision of how planetary systems are formed. The most intriguing characteristic was the presence of multiple bright and dark rings. Only five years ago, ALMA has discovered these structures in a large number of disks. The origin of radial substructures is still under debate, but we are sure that they are related to the formation of planetary systems. They could be the consequence of planets already formed or they could be the places where new planets will be formed. An answer to this question requires of studying the dust properties in bright and dark rings. However, we have also realized that this task is not easy even with ALMA. Bright rings seems to be associated with high density dust and they appear optically thick at ALMA wavelengths, making necessary to add observations with similar quality at longer wavelengths. Here, we present an analysis of the highest quality images available at the moment from the HL Tau disk. These images were obtained with ALMA and the VLA, and they cover a wide range of wavelengths, from 0.9 to 8 mm. The high angular resolution and sensitivity allows to separate emission from the substructures and study their dust properties. With a minimum number of assumptions, we are able to obtain dust temperature, density and maximum particle size with a physical resolution of only 7.5 au. We find that substructures at the external part of the disk (>50 au) are most probably related to the presence of a (porto)planet in an orbit of 80 au, but the internal substructures (<50 au) are more likely related to the presence of ice lines.

On the coagulation and fragmentation of dust in Protoplanetary disks

Kimran Dhaliwal (University of Warwick)

Recent images of protoplanetary disks reveal substructures in exquisite detail that are often linked to forming planets. Such planets can perturb the dust and gas profiles in the disk which can explain gaps and rings and may lead to the formation of a pressure maximum. Due to inwards radial drift, dust grains can become trapped at pressure maxima which may accelerate the formation process. However, due to computational expense, dust coagulation is often left out of simulations. To fully understand the processes at play and their effects on young planets and their dust environments, it is important that hydrodynamical simulations are coupled with dust coagulation and fragmentation physics.

Dynamical effect of the dust back-reaction at the water snowline

Matías Gárate (Max Planck Instutite for Astronomy) 

In protoplanetary disks drag forces determine the interaction between gas and dust. Typically, dust drift inwards (following the pressure gradient), while the gas undergoes viscous evolution. However, in regions such as the water snowline, the dust back-reaction can become strong enough to stop (or reverse) the gas flow. In this work we describe the dynamical effect of the dust back-reaction, and characterize when it becomes important for the global disk evolution.

Connecting gas-phase volatile depletion to primordial planetesimal compositions

Sebastiaan Krijt (University of Exeter)

New disc models designed to explain the observed depletion of C and O in the warm molecular layer lead to predictions for midplane pebble compositions. These predictions can be compared to constraints of (primordial) planetesimal compositions from the solar system or beyond, providing insights into the timing and location of planetesimal formation.

Effect of Dust Coagulation on the Sub-structures in Protoplanetary Disks

Yaping Li (Los Alamos National Laboratory)

Vortices and ringed sub-structures in protoplanetary disks (PPDs) have gained much interest recently due to their importance in interpreting observations and understanding the planetesimal formation. By performing global 2D high-resolution hydrodynamical simulations, we present how the dust size growth affects the vortices and ringed structures produced by an embedded planet in disks. For the vortices induced by a high mass planet embedded in a low viscosity disk, the dust size distribution is quite non-uniform inside the vortex. Both large (∼millimeter) and small (tens of microns) particles contribute strongly to affect the gas motion within the vortex, which results in a significant impact on the vortex lifetime. After the initial gaseous vortex is destroyed, the dust spreads into a ring with a few remaining smaller gaseous vortices. At late time, the synthetic dust continuum images for the coagulation case show as a ring inlaid with several hot spots at the 1.33 mm band, while only distinct hot spots remain at 7.0 mm. For the multiple ringed structures produced by an embedded planet, we find that if the planet does not open a gap quickly enough, the formation of an inner ring is impeded due to dust coagulation and subsequent radial drift.


Characterizing the dust content of disk substructures in TW Hya

Enrique Macías (Joint ALMA Observatory)

A key piece of information to understand the origin and role of protoplanetary disk substructures is their dust content. In particular, disk substructures associated with gas pressure bumps can work as dust traps, accumulating grains and reaching the necessary conditions to trigger the streaming instability. In order to shed some light on the origin and role that disk substructures play in planet formation, we aim at characterizing the dust content of substructures in the disk of TW Hya. We present Atacama Large Millimeter Array (ALMA) observations of TW Hya at 3.1 mm with ~50 milliarcsecond resolution. This new data were combined with archival high angular resolution ALMA observations at 0.87 mm, 1.3 mm, and 2.1 mm. We analyze this multi-wavelength data to infer a disk radial profile of the dust surface density, maximum particle size, and slope of the particle size distribution. Most previously known disk substructures are resolved at the four wavelengths. Our multi-wavelength analysis of the dust emission shows that the maximum particle size in the disk of TW Hya is >1 mm. The inner 20 au are completely optically thick at all four bands, which results in the data tracing different disk heights at different wavelengths. Coupled with the effects of dust settling, this prevents the derivation of accurate density and grain size estimates in these regions. At r>20 au, we find evidence of the accumulation of large dust particle at the position of the bright rings, indicating that these are working as dust traps. The total dust mass in the disk is between 250 and 330 M⊕, which represents a gas-to-dust mass ratio between 50 and 70. Our mass measurement is a factor of 4.3-5.7 higher than the mass that one would estimate using the typical assumptions of large demographic surveys. Overall, our results indicate that the ring substructures in TW Hya are ideal locations to trigger the streaming instability and form new generations of planetesimals.

Rapid Formation of Rocky Planets by Chondrule Accretion

Ake Nordlung (Niels Bohr Institute,  Univ. of Copenhagen)

Using nested-grid, high-resolution 3-D hydrodynamic simulations of gas and particle dynamics in the vicinity of Mars- to Earth-mass planetary embryos, we show that rocky planets such as Earth and Mars can form in of the order of 1 Myr, by accreting solids in the form of mm-size chondrules, rather than the cm-dm size solids that are often assumed in “pebble accretion” models.  The simulations (detailed in Popovas et al, 2018MNRAS.479.5136P and 2019MNRAS.482L.107P) extend from the surface of the embryos to a few vertical disc scale heights, with a spatial dynamic range of order 105.  We find that, due to cancellation effects, accretion rates are to lowest order independent of disc surface density, while varying inversely with particle size. As a result, we can estimate accurate growth times for specified particle sizes. For 0.3-1 mm size particles the growth time from a small seed is  about 1.5 million years for an Earth-mass planet at 1 au and about 1 million years for a Mars mass planet at 1.5 au.  These finding, which are robust – given only the assumptions that accretion takes place in a local pressure maximum (“pressure trap”) and that the dust-to-gas ratio is at least of order 1% – are significant, since it is well known from meteoritic studies that chondrules were abundantly present in the early solar system, and because it has recently been shown by cosmochemical analysis that most chondrules formed in the first million year after formation of the solar system.

Impact of disk demographics on the formation of Giant Planets through pebble accretion

Thomas Ronnet (Lund Observatory) 

Recent observations suggest that disks around type II protostars do not contain enough dust to account for the observed exoplanet population. Younger disks appear to be more massive, hinting towards the onset of planet formation in the earliest stages of star formation and the rapid assembly of planetary cores. We investigate planet formation through pebble accretion in young disks and discuss the outcome in terms of the observed dust disk mass distribution  around class 0 protostars. We find that giant planet formation is possible only within the 30% most massive disks. Giant planets can form at large orbital distances (>10 au) but should be rare, in qualitative agreement with observational inferences.

Gaps and rings at ice lines: Icy pebbles and rocky dust

Katrin Ros (Lund University)

We modelled particle growth by condensation around the water ice line, including the important difference between nucleation of ice on bare rock, and deposition of vapour on already icy particles. The result is a bimodal size distribution with fast-growing icy pebbles locally at the ice line and small, rocky dust particles spreading out over the disc. This is consistent with substructures forming at ice lines, and with the ice line being a preferential location for growth towards planets.  

Dust Dynamics and Implications for Planetesimal Formation in Turbulent Protoplanetary Disks

Ziyan Xu (Peking University)

Planetesimal formation from dust grains has long been one of the least understood processes in planet formation. Recent observations of ring-like substructures in protoplanetary disks indicate dust concentration in axisymmetric gas pressure bumps, but it is unclear whether such dust rings can be precursors to planetesimal formation. In laminar environments, planetesimal formation is widely believed to be the outcome of dust clumping by the streaming instability, triggered by the dust feedback to the gas drag force in a background pressure gradient. However, forming planetesimals generally requires super-solar solid abundances, as expected in dust rings, and the streaming instability is unlikely to operate in pressure bumps. In addition, the bulk disk is believed to be weakly turbulent. We conduct 3D non-ideal MHD simulations with Athena code to study dust dynamics in weakly turbulent disks, focusing on the role of dust feedback. We find that in a smooth disk, dust feedback modifies turbulence properties, enhances dust settling, and reduces dust layer thickness. Dust clumping is seen in the simulations, likely related to magnetic zonal flows. Introducing a gas pressure bump in our simulations leads to dust trapping in a ring. Dust feedback further affects turbulence properties and promotes dust trapping by making the dust ring narrower. We find evidence of dust clumping in the ring for near-solar global solid abundance of mm-sized dust. These results suggest that dust rings are preferable locations for planetesimal formation, with implications for the observed ring structures.

Solid accretion onto planetary cores in radiative disks

Apostolos Zormpas (University Observatory / LMU Munich)

The solid accretion rate, which is necessary to grow gas giant planetary cores within the disk lifetime, has been a major constraint for theories of planet formation. We measured the solid accretion rate efficiency on planetary cores of different masses embedded in their birth disk by means of 3D radiation-hydrodynamics, where we followed the evolution of a swarm of embedded solids of different sizes. We found that by using a realistic equation of state and radiative cooling, the disk at 5 au is able to efficiently cool and reduce its aspect ratio. As a result, the pebble isolation mass is reached before the core grows to 10 Earth masses, thus fully stopping the pebble flux and creating a transition disk. Moreover, the reduced isolation mass halts the solid accretion before the core reaches the critical mass, leading to a barrier to giant planet formation, and this explains the large abundance of super-Earth planets in the observed population.


Planet formation and disk evolution in Class 0/I systems          

ALMA Studies of Eruptive Stars

Antonio Hales (ALMA/NRAO)

It is now believed that stars acquire most of their mass in short episodes of accretion outbursts. This episodic accretion picture has replaced the traditional steady state accretion model and is changing our understanding on how stars gain their mass (and the origin of the IMF), binary formation, planet formation, the luminosity spread in young clusters, disk chemistry and snowline migration. Despite its relevance, the physical mechanisms responsible for episodic accretion remain poorly understood. In this poster we present recent observational and modelling advancements aimed at constraining the physical properties of outbursting sources to help understand what drives this important phase of star formation."

Protostellar Disks as Sites of Early Phase Planet Formation

Aleksandra Kuznetsova (American Museum of Natural History)

Embedded systems experience infall from their envelopes, which can have a range of dynamical consequences on the nascent disk. I will present a new generalized model of infall onto disks, accounting for the three dimensional and heterogeneous nature of protostellar envelopes, and discuss the range of parameters for which infall mediated structure formation and transport can have significant consequences for early phase planet formation.

(Note that this poster includes embedded animations that will not work in the Zenodo viewer. Please download the PDF and open it with Adobe Acrobat Reader if you would like to see the animations)

Five years after HL Tau: The First Hydrostatic Core!

Dary Ruiz-Rodriguez (National Radio Astronomy Observatory)

It is theoretically predicted that in between a starless core and a protostar, i.e. before the beginning of the Class 0 phase, a collapsing molecular core initially forms a central hydrostatic object known as the First Hydrostatic Core (FHSC). Several theoretical studies have investigated the physical properties of these FHSCs, however, this very short evolutionary stage has been highly elusive and challenging to prove observationally. As a matter of fact, many candidate FHSCs have been identified, but none have been definitively confirmed as such. Therefore, detecting observationally these objects is of central importance in studies of the earliest phases of low-mass star formation. Since more than 50 years ago (Larson 1969), astronomers have been pursuing an observational verification of the FHSCs, which would provide a laboratory for probing and understanding the earliest stellar stages and the formation of their associated protoplanetary disks, currently poorly constrained. Here, we present the robust detection of a FHSC, the first of its kind, by using the Atacama Large Millimeter/submillimeter Array (ALMA). Based on a kinematic modeling of the spherical rotating collapse phase, we estimate the characteristic physical properties of the object (central mass and accretion rate), which match those predicted for FHSCs.

How much dust is available for planet formation?

Lukasz Tychoniec (ESO Garching)

In recent years evidence has been building that planet formation starts early, in the first 0.5 Myr. Therefore the physical conditions at the early stages of star formation are crucial to understanding the origin of the planetary systems. We use Atacama Large Millimeter/submillimeter Array (ALMA) observations of embedded disks in Perseus together with existing Very Large Array (VLA) data to provide a robust estimate of disk masses and to compare the Perseus survey of dust masses with other ALMA surveys of young and mature disks. We put the disk mass estimates in the context of known exoplanetary systems. The dust masses of disks in Class 0/I are significantly larger than those inferred for Class II disks in other regions. The masses of Class 0 and I disks in Perseus can produce the observed exoplanet systems with efficiencies acceptable by planet formation models. The most massive observed exoplanets can still be produced by the most massive Class 0 disks with an efficiency of 15%, higher efficiencies are needed if the planet formation starts in Class I. Constraining the starting point of the planet formation and the mass reservoir available is crucial for modern models of the planet formation.

A Study of Millimeter Variability in FUor Objects

John Wendeborn (Boston University)

FUor objects (a class of outbursting, young, pre-main sequence stars) have been shown to be variable at millimeter wavelengths on timescale of ~years. We find that the object V1735 Cyg exhibited a ~80% increase in 2.7 mm flux between 2014 and 2017. It does not show corresponding variability at optical/NIR wavelengths, but shows a decrease in the millimeter spectral index. This implies that the mllimeter flux increase may be due to an accretion event which increased the contribution from free-free emission in the jet. This result shows that an FUor disk mass obtained from millimeter flux may be overestimated if the object has recently undergone recent accretion activity.


Late and debris disks                                                                      

Resolving the outer ring of HD 38206 using ALMA

Mark Booth (AIU, Friedrich Schiller University, Jena)

HD 38206 is an A0V star in the Columba association, hosting a debris disc first discovered by IRAS. Further observations by Spitzer and Herschel showed that the disc has two components, likely analogous to the asteroid and Kuiper belts of the Solar System. The young age of this star makes it a prime target for direct imaging planet searches. Possible planets in the system can be constrained using the debris disc. Here we present the first ALMA observations of the system's Kuiper belt and fit them using a forward modelling MCMC approach. We detect an extended disc of dust peaking at around 180 au with a width of 140 au. The disc is close to edge on and shows tentative signs of an asymmetry best fit by an eccentricity of 0.25. We use the fitted parameters to determine limits on the masses of planets interior to the cold belt. We determine that a minimum of four planets are required, each with a minimum mass of 0.64 Jupiter masses, in order to clear the gap between the asteroid and Kuiper belts of the system. If we make the assumption that the outermost planet is responsible for the stirring of the disc, the location of its inner edge and the eccentricity of the disc, then we can more tightly predict its eccentricity, mass and semimajor axis.

What lies beyond Exo-Jupiters? A High Resolution study of q¹ Eridani

Joshua Lovell (Institute of Astronomy, University of Cambridge)

ALMA Band 6 and 7 observations of the >1Gyr F9V star q1 Eri (HD10647, HR506) are presented, a system with a known ~2 au radial velocity planet and debris disk. These resolved images detect the broad debris disk, inclined by ~76deg to the plane of the sky with a maximum brightness at ~82 au. The emission is asymmetric; the flux is higher in the SW than the NE and the star is closer to the SW ansa. HST data are also presented which show that the scattered light is more radially extended in the NE. With modelling, we show the SW ansa asymmetry is broadly consistent with an extended clump on the inner edge of the disk. We assess the inner edge and clump as consistent with perturbations from an inner planet. If the modelled vertical aspect ratio is due to dynamical interactions in the disk, we constrain the size of perturbers and find these to be consistent with the lower limit on the maximum planetesimal size, estimated from the collisional lifetime of bodies in the disk.


Protoplanetary disk demographics                                               

An ALMA survey of λ Orionis disks: from supernovae to planet formation

Megan Ansdell (NASA Headquarters)

Protoplanetary disk surveys by ALMA are now probing a range of environmental conditions, from low-mass star-forming regions to massive OB clusters. Here we conduct an ALMA survey of protoplanetary disks in λ Orionis, a 5~Myr old OB cluster in Orion, with dust mass sensitivities comparable to the surveys of nearby regions (~0.4 M_Earth). We assess how massive OB stars impact planet formation, in particular from the supernova that may have occurred ~1 Myr ago in the core of λ Orionis; studying these effects is important as most planetary systems, including our Solar System, are likely born in cluster environments. We find that the effects of massive stars, in the form of pre-supernova feedback and/or a supernova itself, do not appear to significantly reduce the available planet-forming material otherwise expected at the evolved age of λ Orionis. We also compare a lingering massive "outlier" disk in λ Orionis to similar systems in other evolved regions, hypothesizing that these outliers host companions in their inner disks that suppress disk dispersal to extend the lifetimes of their outer primordial disks.

Testing magnetospheric accretion models for low mass young stars: Hydrogen lines in Lupus

Maria Jose Colmenares (Universidad de Los Andes)

The study of emission lines formed in the magnetospheric accretion flows around young stars allows us to constrain the thermal and geometrical properties of the flows, which can later help us to determine accretion rates more accurately. Our main goal is to prove the validity of the magnetospheric accretion models ( Muzerolle et al. 2001) by comparing theoretical fluxes with those calculated from observations. We use the de-reddened fluxes data from Alcalá et al.(2014,2017) of 37 stars from the Lupus region, ranging from K5 to M4, as well as the accretion rates calculated in that paper. We study Halpha, BrGamma and PaBeta, from which we conclude that for higher accretion rates the magnetosphere is cold, wide and close to the star and for lower accretion rates the flows are further away from the star, narrow and have higher temperatures; this can be seen throughout the three lines studied

Revisiting the IR line decrements of T Tauri stars with magnetospheric accretion models.

Jesús Vicente Diaz Aponte (Universidad de Los Andes (VE))

The magnetospheric accretion model has been successful in reproducing the flux lines from fluxes of emission lines such as Halpha in young (1 Myrs to 10 Myrs old) accreting stars with masses that range from the substellar limit to the Herbig Ae/Be stars. In this model, the emission lines arise in hot (T ~ 10000K) flows joining the disk and the star. However, Bary et al 2008 conducted a variability survey in the Taurus-Auriga star formation region, in which the flux of hydrogen Paschen and Bracket lines were measured in multiple epochs, finding that the Paschen and Bracket decrements could be explained with low temperatures (below 5000K) recombination models. In this contribution, we attempt to reproduce the Bary et al. decrement for Paschen and Brackett emission lines for 15 stars in their sample using instead of the magnetospheric accretion model. We find that the decrements can be explained using temperatures from 8000K to 11000K consistent with the temperatures required to model the H Balmer lines. 

On the Accuracy of the ALMA Flux Calibration in the Time Domain and across Spectral Windows

Logan Francis (University of Victoria)

A diverse array of science goals requires accurate flux calibration of observations with the Atacama Large Millimeter/submillimeter array (ALMA); however, this goal remains challenging due to the stochastic time-variability of the “grid” quasars ALMA uses for calibration. In this work, we use 343.5 GHz (Band 7) ALMA Atacama Compact Array observations of four bright and stable young stellar objects over seven epochs to independently assess the accuracy of the ALMA flux calibration and to refine the relative calibration across epochs. The use of these four extra calibrators allows us to achieve an unprecedented relative ALMA calibration accuracy of ∼3%. On the other hand, when the observatory calibrator catalog is not up to date, the Band 7 data calibrated by the ALMA pipeline may have a flux calibration poorer than the nominal 10%, which can be exacerbated by weather-related phase decorrelation when self-calibration of the science target is either not possible or not attempted. We also uncover a relative flux calibration uncertainty between spectral windows of 0.8%, implying that measuring spectral indices within a single ALMA band is likely highly uncertain. We thus recommend various methods for science goals requiring high flux accuracy and robust calibration, in particular, the observation of additional calibrators combined with a relative calibration strategy, and observation of solar system objects for high absolute accuracy.

Protoplanetary disks meet artificial neural networks: revisiting the viscous disk model and updated disk masses

Alvaro Ribas (European Southern Observatory, Chile)

We model the SEDs of 23 protoplanetary disks in the Taurus-Auriga star-forming region using detailed disk models and a Bayesian approach. This is made possible by combining these models with artificial neural networks to drastically speed up their performance. Such a setup allows us to confront $\alpha$-disk models with observations while accounting for several uncertainties and degeneracies. Our results yield high viscosities for many sources, which is not consistent with recent measurements of low turbulence levels in disks. This inconsistency could imply that viscosity is not the main mechanism for angular momentum transport in disks, and that alternatives such as disk winds play an important role in this process. We also find that our SED-derived disk masses are systematically higher (median difference of a factor of $\sim$3 higher) than those obtained solely from (sub)mm fluxes, suggesting that part of the disk emission could still be optically thick at (sub)mm wavelengths. This effect is particularly relevant for disk population studies and alleviates observational tensions between the masses of protoplanetary disks and exoplanetary systems.