| | Thursday, October 8 | |
| Chair: A. Miotello | | |
| 14:00-14:30 | Giovanni Rosotti | The conditions of planet-forming discs | abstract |
| | Abstract: Thanks to ALMA, we are now detecting structures like gaps, rings and spirals in proto-planetary discs, commonly attributed to young, forming planets. But at the same time, the revolutionary ALMA datasets are important for another reason: they allow us to characterise the environment in which planets form. This characterisation is of fundamental importance to understand planet formation: the disc environment determines how planets accrete solids and grow to the point of eventually becoming observable. I will show through various examples of my work how to conduct this characterisation. I will focus in particular on the question of how turbulent these discs are and the related question of whether turbulence (or, as frequently called in this context, viscosity) is the dominant mechanism of angular momentum transport. To tackle these questions, I will illustrate two different approaches. The first one consists in using the measurements of the bulk properties, such as masses, radii and mass accretion rates, now available for large samples of discs. The existence of a correlation between mass accretion rates and disc masses suggests that discs evolution is driven by turbulence/viscosity. However, we can exclude that discs are highly turbulent, as shown for example by the small sizes of the bulk of the disc population. The second approach consists in a detailed view of individual discs. I will show in particular how the analysis of the disc gas rotation curve is a powerful way to measure the amount of turbulence. The discs for which this analysis is possible are compatible with having a low degree of turbulence, but in this case grain growth cannot have proceeded beyond mm-size.
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| 14:30-15:00 | Farzana Meru | Spirals, rings and gaps: using disc structure to infer planet formation processes | abstract |
| | Abstract: We have recently entered an era of high resolution, spatially resolved observations of protoplanetary discs, which are revealing exciting disc structures. Such features give us clues on the protoplanetary disc and planet formation processes. I will discuss some of the recent theoretical advances we have made in trying to understand the origin of these structures, to ultimately understand disc processes and planet formation.
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| 15:00-15:20 | Carlo F. Manara | Disk evolution and planet formation across time and space | abstract |
| | Abstract: In the last years we have expanded our understanding of when, where, and how planets form. In particular, we are starting to constrain the timescale on which planets form, and to have a better understanding of the properties of their natal disks. Whether these properties of protoplanetary disks are similar in different stellar environments is still matter of debate. The mechanisms driving disk evolution, which are tested by combining spectroscopic and millimetre observations of disks and their stars, can be different in more massive clusters with respect to the nearby low-mass star-forming regions.
I will report on our extensive surveys in several star-forming regions from the nearby Lupus and Chamaeleon I regions, to the further away sigma Orionis and lambda Orionis cluster, carried out with VLT/X-Shooter spectroscopy and with high-resolution ALMA sub-mm data, and on new MUSE observations of externally photoevaporated disks in the Orion Nebula Cluster, to show what we have learned on how protoplanetary disks evolve.
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| 15:20-15:35 | | BREAK & PHOTO | |
| 15:35-16:05 | Richard Booth | Fingerprints of giant planets in the composition of solar twins | abstract |
| | Abstract: The Sun shows a ∼10 per cent depletion in refractory elements relative to nearby solar twins. It has been suggested that this depletion is a signpost of planet formation. The exoplanet statistics are now good enough to show that the origin of this depletion does not arise from the sequestration of refractory material inside the planets themselves. This conclusion arises because most sun-like stars host close-in planetary systems that are on average more massive than the Sun's. Using evolutionary models for the protoplanetary discs that surrounded the young Sun and solar twins, we demonstrate that the origin of the depletion likely arises due to formation of a transition disc via the trapping of dust exterior to the orbit of a forming giant planet. In this scenario, a forming giant planet opens a gap in the gas disc, creating a pressure trap. If the planet forms early enough, while the disc is still massive, the planet can trap ≳100 M⊕ of dust exterior to its orbit, preventing the dust from accreting on to the star in contrast to the gas. Forming giant planets can create refractory depletions of ∼ 5-15 per cent, with the larger values occurring for initial conditions that favour giant planet formation (e.g. more massive discs that live longer). The incidence of solar twins that show refractory depletion matches both the occurrence of giant planets discovered in exoplanet surveys and `transition' discs that show similar depletion patterns in the material that is accreting on to the star.
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| Chair: M. Hutchison | | |
| 16:05-16:35 | Rebecca Nealon | Misalignments, warps and precession | abstract |
| | Abstract: Current observations from ALMA and SPHERE have identified unique features in protoplanetary discs around young stars, including warps in the disc (e.g. TW Hya, HD 100453 and HD 135344B) and strongly misaligned inner discs (e.g. HD 100546, HD143006). The rate that we identify such discs suggest that misalignments and warps are commonplace, and as such must be taken into account in the complete picture of disc and planet formation. From a theoretical perspective I will explore disc structures that are formed due to misaligned planets, massive inner companions and outer companions (both bound and unbound). Tying these to the observational picture, I will show which scenarios are most likely occurring in the warped discs we have already observed. I will also demonstrate the power of using numerical simulations to predict observational features such as "rocking shadows".
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| 16:35-16:50 | | BREAK | |
| 16:50-17:10 | Lisa Wölfer | A highly non-Keplerian protoplanetary disk - Spiral structure in the gas disc of CQ Tau | abstract |
| | Abstract: In the past years, high angular resolution observations have revealed that circumstellar discs appear in a variety of shapes with diverse substructures being ubiquitous. This has given rise to the question of whether these substructures are triggered by planet-disc interactions. Besides direct imaging, one of the most promising methods to distinguish between different disc shaping mechanisms is to study the gas content of the disc in terms of its kinematics. Apart from `kinks` in the iso-velocity contours, the deviations of the rotation profile from Keplerian velocity can be used to probe perturbations in the gas pressure profile that might be caused by embedded (proto-) planets. In this work we analyze the gas brightness temperature and kinematics of the transitional disc around the nearby, intermediate mass star CQ Tau in order to resolve and characterize substructure in the gas, caused by possible perturbers. For our analysis we use spatially resolved ALMA observations of the three CO isotopologues 12CO, 13CO and C18O (J=2-1) from the disc around CQ Tau. We further extract robust line centroids for each channel map and fit a number of Keplerian disc models to the velocity field. The gas kinematics of the CQ Tau disc present non-Keplerian features, showing bent and twisted iso-velocity curves in 12CO. Significant spiral structure is detected in both the brightness temperature and the rotation velocity after subtraction of an azimuthally symmetric model, which may be tracing planet-disc interactions with an embedded planet or low-mass companion. We identify three spirals, two in the brightness temperature and one in the velocity, spanning a large azimuth and radial extent. A symmetric pair of shadows may be present in both the integrated and peak intensity, which may be indicative of an inner disc misaligned with respect to the outer disc. The kinematics are however strongly dominated by the spiral feature, making it difficult to constrain any characteristics of smaller features like this potential warp.
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| 17:10-17:40 | Richard Teague | Observing the Dynamics of Planet-Disk Interactions | abstract |
| | Abstract: ALMA has revealed a stunning variety of dust substructures, such as gaps, rings and spirals, highly indicative of planet-disk interactions. In parallel, high spectral resolution observations of molecular line emission are starting to similar levels of structure, both in their emission distributions but also their kinematical structures, which can only be traced through probes of the gas. I will present recent work which explores how we can extract exceptionally precise velocity measurements from such data. In particular, I will highlight how we can now detect what is likely the kinematical signatures of embedded planets, such as the spiral wakes driven by a young planet or meridional flows, large-scale vertical flows of gas onto a protoplanet. I will discuss the implications that these flows have on our understanding of the volatile delivery process and how they can shape the atmospheric composition of gas giants. I will conclude by demonstrating how we can transform ALMA into a planet hunting instrument, allowing us to probe the earliest stages of planet formation.
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| 17:40-18:00 | Peter Rodenkirch | Constraining the origin of non-axisymmetric structures in the HD163296 disk | abstract |
| | Abstract: High resolution ALMA observations like the DSHARP campaign revealed a variety of rich substructures in numerous protoplanetary disks. These structures consist of rings, gaps and asymmetric features. It is debated whether planets can be accounted for these substructures in the dust continuum. Characterizing the origin of asymmetries as seen in HD 163296 might lead to a better understanding of planet formation and the underlying physical parameters of the system. We test the possibility of the formation of the crescent shaped asymmetry in the HD 163296 disk through planet disk interaction. The goal is to obtain constraints on planet masses and eccentricities and disk viscosities. Methods. Two dimensional, multi-fluid, hydrodynamical simulations are performed with the FARGO3D code including three embedded planets. Dust is described with the pressureless fluid approach and is distributed over eight size bins. Resulting grids are post-processed with the radiative transfer code RADMC-3D and the CASA software to model synthetic observations. We find that the asymmetry can be qualitatively modeled with a Jupiter mass planet at a radial distance of 48 au. Dust is trapped preferably in the trailing Lagrange point L5 with a mass of 10 to 15 earth masses. The observation of such a feature confines the level of viscosity and planetary mass. Increased values of eccentricity of the innermost Jupiter mass planet damages the stability of the asymmetric feature and does not reproduce the observed radial proximity to the first prominent ring in the system. Generally, a low level of viscosity (α ≤ 2 · 10−3) is necessary to allow the existence of such an asymmetry. Including dust feedback the leading point L4 can dominantly capture dust for dust grains with an initial Stokes number ≤ 3.6 · 10−2 corresponding to a grain size of ≈ 5 mm. Masses larger than ≈ 0.5 Jupiter masses for the second planet at 83 au may lead to vortices and asymmetric dust trapping instead.
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