Core 2 Disk 2

17 mai 2021, 09:00 → 28 mai 2021, 17:00 Europe/Paris

RATIONALE

Understanding the formation of stars and the formation of planets,are both cornerstone challenges in modern astronomy. These highly multi-physics and multi-scale problems are tightly linked through the formation and evolution of proto-planetary discs. As such, they should ideally be apprehended simultaneously. In practice however, due to the great variety of instruments and techniques that must be used as well as the profusion and complexity of physical processes, the field is traditionally subdivided in three communities addressing specific questions all relevant to reach a global understanding, including:  

-the formation, collapse and fragmentation of dense cores which also addresses the issue of centrifugally supported discs formation and early evolution around the youngest protostars (i.e. younger than typically 1 Myr)  

-the evolution of protoplanetary discs whose main objectives are the origin of the angular momentum transportation, the dynamics of gas and dust as well as the growth from grains to planetesimals  

-the study of solar nebulae constituents such as gas, grains and pebbles from a dynamical and chemical perspectives
 
Recent facilities such as the space observatory Herschel, and ground based observatories like ALMA and the VLT/VLTI have already started to revolutionise the field of star and planet formation. The forthcoming James WebbSpace Telescope (JWST), and potentially in the more distant future ELT, ARIEL and SPICA, are expected to provide the observational tools to bring our understanding of planetary origins and diversity to a new level. These new observational tools, as well as the development of comprehensive models, numerical simulations including more and more physical ingredients as well as laboratory measurements, finally open the door to meaningful combination of tools and results from the different communities. 
 
The opening of these new facilities, telescopes, super computers and laboratory experiments, as well as the significant progresses made on the theory side, make the organisation of collaborative workshop particularly timely. Not only to bring together the three communities but also the observers,the theorists and the instrumentalist who are solely altogether present.

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lundi 17 mai

11:30 → 12:00 The role of streamers on star formation: JAIME PINEDA

Dense cores are the places where stars are formed within the supersonic Molecular Clouds. These dense regions (n~10^5 cc) are cold (T~10 K) and display subsonic levels of turbulence (Mach ~ 0.5), and represent the initial conditions for both star and disk formation. However, the influence of the parental core properties on the disk formation process is still not well constrained, and it is crucial to study dense cores with interferometers to better understand the dense core and disk connection. Recent NOEMA observations of a Class 0 object reveal a previously unseen large-scale (~10,000 au) streamer of fresh gas from the surrounding dense core down to the disk scales. This streamer is unrelated to the outflow, and it is well modeled using a free-falling streamline. We estimate an infall rate comparable to the accretion rate onto the protostar. This clearly shows that accretion via streamer can have an important role in star/disk formation. Finally, I will present new results of streamers on other sources showing similar evidence for streamers and discuss their possible role that streamers would play affecting the dust properties at disk forming scales.

12:00 → 12:30 Monte Carlo dust radiative transfer of polarised radiation: SIEBENMORGEN RALF

Dust obscured objects cannot be studied directly in the UV/optical, since the dust shields most of the visible light. To derive the UV/optical component or to constrain the morphological structure from available IR/submm observations, a detailed model of the interaction of photons with the dust is required. The problem is to solve the radiative transfer (RT) equation. Analytically, the RT problem can only be done in some simple configurations, for example by assuming spherical or disk symmetry in which either scattering or absorption is neglected and the wavelength dependency of the dust cross section is strongly simplified, e.g. by a gray body. Nature, however, is usually not well approximated by such assumptions and numerical modeling is the only way to solve this problem. In the talk a Monte Carlo Radiative Transfer scheme for solving the radiative transfer of polarised light in dust enshrouded media in arbitrary geometries is presented and results of different treatments for computing cross sections of spheroidal dust particles are compared.

12:30 → 13:00 Institut Pascal Presentation: DENIS ULLMO

13:00 → 14:00 Lunch

14:00 → 14:30 A ringed Class I dust disk accretes envelope material via an accretion streamer: DOMINIQUE SEGURA COX

Ringed protoplanetary dust disks, in the Class II phase of low-mass star formation when the envelope has mostly dispersed, have been found in abundance in recent years with high-resolution ALMA observations. These ringed disks have been often interpreted as evidence of planet formation, caused by planetesimal-disk interactions. I will present ALMA observations of a younger embedded Class I protostar which has a ringed dust disk (5 au resolution data) as well as a larger-scale infalling streamer of gas 1500 au in length from the envelope to the disk (100 au resolution data). The dust rings are the least-evolved example of rings in a protostellar disk known to date, indicating that stable zones of grain growth---required for the first steps of planet formation---are already in place during the early embedded phase of star formation. There are indications that at least one of the dust rings may be associated with the CO snowline, and this may be a hint that in the embedded phases any dust rings seen may be precursors to the first generation of planetesimals which can in turn sculpt the disk into more sharply defined rings at later times. Further, the ringed dust disk is fed envelope material via the 1500 au gas streamer, influencing the disk composition and potentially even triggering the initial over densities in the disk needed to form the dust rings. This work highlights the need for multi-scale dust and gas observations to understand the first steps of planet formation in embedded disks.

14:30 → 15:30 DISCUSSION: Leader SOC - Anaëlle MAURY/Nathalie YSARD

mardi 18 mai

11:30 → 12:00 Numerical simulations of grain growth revisited: GUILLAUME LAIBE

One of the grand challenge of planet formation consist of performing 3D simulations of young dusty stellar systems that include grain growth and fragmentation self-consistently. Up to now, this task was considered as almost computationally inaccessible, due to the prohibitive computational cost associated to algorithms solving for the coagulation equation. I will show how connecting mathematical, physical, numerical and computational aspects of the coagulation equation led to the design of a novel scheme capable of addressing this challenge (Lombart and Laibe 2020).

12:00 → 12:30 Search for grain growth toward the center of a prestellar core: ANA CHACON-TANARRO

The study of dust grains in the earliest phases of star formation is crucial for understanding the chemical structure of dense cloud cores and the future evolution of solids in protoplanetary disks. It is however not clear if dust growth starts before star formation begins. Thus, we studied L1544, one of the most centrally concentrated prestellar cores on the verge of star formation, and with a well-known physical structure. Moreover, previous studies predict an increase in the dust opacity by a factor of 4 towards the center of L1544, which suggests dust grain coagulation towards its center. In order to test this theory, L1544 was observed using some of the newest continuum facilities: NIKA at the IRAM 30m telescope, MUSTANG-2 at the GBT and AzTEC at the LMT, observing at 1.2 and 2 mm, 3.3 mm, and 1.1 mm, respectively. The observations done at the IRAM 30m telescope show no indication of grain growth in this core. However, we show that the spatial resolution and the sensitivity of the observations are not sufficient for detecting the predicted effect, and that interferometers, such as ALMA, should be able to find evidence for grain growth in the inner 2000 au of the core. Newer results obtained with the maps observed at the GBT and the LMT show gradients in the dust opacity across the cloud, which is consistent with variations in the thickness of the ice mantles formed on the dust grains surfaces. These observations also show that previous models of the cloud need to be revised and include a new physical description of the cloud. A simple analytical grain growth model predicts the presence of grains of a few micrometers within the central 2000 au for the derived density and temperature profiles.

12:30 → 14:00 Lunch

14:00 → 14:30 Observing forming planets.: CHRISTOPHE PINTE

We still do not understand how planets form, or why extra-solar planetary systems are so different from our own solar system. Recent observations of protoplanetary discs have revealed rings and gaps, spirals and asymmetries. These features have been interpreted as signatures of newborn protoplanets, but the exact origin is unknown, and remained until recently poorly constrained by direct observation. In this talk, I will show how high spatial and spectral resolution ALMA observations can be used to detect embedded planet in their discs, and discuss the implications on our understanding of planet formation.

14:30 → 15:30 DISCUSSION: leader soc - Patrick HENNEBELLE/Emilie HABART/ Eric PANTIN

mercredi 19 mai

11:30 → 12:00 The Disc Miner I: how to look for embedded planets in discs: ANDRES IZQUIERDO

The study of disc kinematics has recently opened up as a promising method to detect unseen planets. However, a systematic, statistically meaningful analysis of such an approach remains missing in the field. I will present recent work on an automated, statistically robust technique to identify kinematical perturbations induced by the presence of planets in gas discs. I will also discuss on the impact of gas gaps and vertical structure on observable velocities, as well as variations in the retrieved perturbations as a function of the mass and azimuth of the planet. Our method, powered by the "discminer" channel-map fitting package, takes advantage of coherent velocity fluctuations to robustly detect planets.

12:00 → 12:30 On the secular evolution of the ratio between gas and dust radii in protoplanetary discs: testing the efficiency of radial drift: CLAUDIA TOCI

Protoplanetary discs are the sites of planetary formation: they provide the dust and gas building blocks to form the exo-planetary systems observed around main sequence stars (see e.g., Testi et al. 2014). According to the analytical theory of Lynden-Bell & Pringle (1974), the gas in protoplanetary discs evolve under the influence of an effective viscosity, conserving angular momentum. Consequently, discs are getting larger with time, a process known as viscous spreading. Dust behaves differently due to the presence of radial drift: the gas exerts a drag force on the dust, that loses angular momentum and quickly drifts inwards towards the star (Weidenschilling 1977). A key problem is to understand how efficient can dust radial drift be. Indeed, because of radial drift we should expect the dust disc size to shrink in time and eventually, due to the very short timescales involved, the dust disc to disappear (Appelgren et al. 2020). However, discs are still observed at a typical age of a few Myr. Thanks to new generation instruments such as ALMA, dust and gas radii of discs can be measured for many young regions (see e.g., Sanchis et al. 2021). In this talk I will show tests of disc evolution models studying the secular evolution of the ratio between the observed dust and gas radius, to test the efficiency of radial drift. Our discs models are evolving considering viscous evolution and the two-population dust model of Birnstiel et al. 2012, that includes grain growth, fragmentation, and radial drift. We also included the feedback of dust onto gas (Laibe & Price 2014). To evaluate the flux of the models we use the radiative transfer code RADMC (Dullemond et al. 2012). Once evaluated the dust and gas radii, we investigate how their ratio evolves as a function of the time. We tested different values of initial disc mass, scale radius and viscosity, covering the range of reasonable values found in the Literature, and we compared our results with the observational findings of young star forming regions such as Lupus (Sanchis et al. 2021). I will show that, for a wide range of initial conditions of the discs, the ratio between the dust and gas radii quickly (after about a Myr) becomes very large ( >5) due to the presence of radial drift, pointing out that radial drift is too efficient in the models. To solve this odd, substructures, routinely resolved in bright, large discs, must be present in most of the sources, although unresolved.

12:30 → 14:00 Lunch

14:00 → 14:30 Compact disks: an explanation to faint CO emission in Lupus disks: ANNA MIOTELLO

ALMA disk surveys have shown that a large fraction of observed protoplanetary disks in nearby SFRs are fainter than expected in CO isotopologue emission. Disks not detected in 13CO line emission are also faint and often unresolved in the continuum emission at an angular resolution of around 0.2 arcseconds. Does this population comprise radially extended and low mass disks - as commonly assumed so far - or is it of intrinsically radially compact disks? A new grid of DALI physical-chemical models of compact disks has been compared with 12CO and 13CO ALMA observations of faint disks in the Lupus SFR. Lupus disks that are not detected in 13CO emission and with faint or undetected 12CO emission are consistent with compact disk models. For disks with a limited radial extent, the emission of CO isotopologues is mostly optically thick and it scales with the surface area: i.e., it is fainter for smaller objects. The fraction of compact disks is potentially between roughly 50% and 60% of the entire Lupus sample. If the fainter end of the disk population observed by ALMA disk surveys is consistent with such objects being very compact, will either create a tension with viscous spreading or require MHD winds or external processes to truncate the disks. An interesting implication to planet formation is that, in such small and optically thick disks, there may be substantial reservoirs of gas for forming Jupiter-like planets within Jupiter’s orbital radius.

14:30 → 15:30 WEEK DISCUSSION: leader Hily-Blant

jeudi 20 mai

11:30 → 12:00 Isotopic ratios as indicators of physical and chemical properties of protoplanetary disks: HIDEKO NOMURA

Isotopic ratios provide a powerful tool for understanding the origins of materials since they are sensitive to physical and chemical properties of objects. We have studied isotope chemistry in the protoplanetary disk (PPD) around TW Hya, one of the best studied PPDs, using a detailed physical model together with comprehensive isotope chemical reaction network. Our result suggests that nitrogen fractionation is sensitive to carbon-to-oxygen elemental abundance ratio (C/O ratio) as well as dust evolution in the disk, while carbon fractionation can also be an indicator of the C/O ratio. Our result suggests that the C/O ratio is high and small dust grains are deleted in the outer disk, compared with the inner disk, in order to reproduce the fractionation profile recently observed by ALMA. I will discuss these chemical and physical properties together with our ALMA observations of some molecular lines.

12:00 → 12:30 The GRAVITY view of young protoplanetary disks' inner regions: LUCAS LABADIE

planet formation and evolution is tightly connected to the physics of young protoplanetary disks, which is an inherently complex problem that requires a multi-wavelength, multi-scale observational approach. In this context, our understanding of the properties of the inner (~0.1-1AU) regions of the disk appears to be highly relevant for the comprehension of the global picture, setting the need for high-angular resolution data. GRAVITY at the VLTI is one of the instruments capable of uniquely addressing these questions in the near-IR range thanks to the milliarcsecond resolution reachable. In the context of the GRAVITY YSO survey, the study of an homogeneous population of Herbig and T Tauri stars provides details on the spatial structuration of the dust associated with the continuum emission. The spectral capabilities of Gravity allows us to derive constraints on the Brackett-gamma line emitting regions in the context of scenarii dominated by magnetospheric accretion or gas in keplerian rotation, as well as on the regions of hot CO emission in more massive YSOs. These results constitute the seed for larger studies that will become possible with the GRAVITY+ upgrade, which anticipated capabilities for the study of YSOs will be briefly presented as well.

12:30 → 14:00 Lunch

14:00 → 14:30 The role of microphysics and non-ideal MHD effects in the formation of protoplanetary disks: BO ZHAO

The formation of rotationally supported discs from magnetized dense cores of molecular clouds is a long-standing problem in star formation, due to the “catastrophic” magnetic braking that transports most angular momentum away from the circumstellar region and suppresses disc formation. Non-ideal MHD effects, especially ambipolar diffusion (AD) and Hall effect, have shown as robust mechanisms to resolve the magnetic braking catastrophe. However, the magnetic diffusivities that determine the efficiency of non-ideal MHD effects are highly sensitive to microphysics. We carry out non-ideal MHD simulations to explore the role of microphysics on disc formation and the interplay between AD and Hall effect during the protostellar collapse. We find that removing the smallest grain population (≤10 nm) from the standard MRN size distribution can greatly enhance the magnetic diffusivities and promote disc formation. In the infalling envelope, AD and Hall effect can operate either with or against each other, yet the combined effect of AD and Hall is to move the magnetic field radially outward relative to the infall matter. We also find that the direction of disc rotation can be bimodal for opposite magnetic polarities, when Hall effect is dominating the collapse process. In addition, microphysics and magnetic field polarity can leave profound imprints on observables including outflow morphology, disc to stellar mass ratio. With the help of AD and Hall effect, disc formation should be relatively common for typical prestellar core conditions, and cores with higher cosmic-ray ionization rate of a few 10^-16 /s can still form small discs of ≤10 AU radius.

14:30 → 15:30 WEEK DISCUSSION: leader Caselli

vendredi 21 mai

11:30 → 12:00 Millimeter-wave polarization of protoplanetary disks due to self-scattering: AKIMASA KATAOKA

Polarimetric observations of protoplanetary disks at millimeter wavelengths have been dramatically developing with ALMA. One of the most dominant mechanisms is the self-scattering of thermal dust emission, but there are contributions of intrinsic polarization of elongated dust grains and it requires modeling approach to discuss its scientific implications. In this talk, We first quickly review the possible mechanisms that may produce the millimeter polarization, and then pick up the HL Tau disk to demonstrate interpretations. We found that self-scattering dominates the 0.88 mm wavelengths but alignment due to gas flow may dominate at 3.1 mm wavelengths. This indicates the grain size to be an order of 100 micron, which is inconsistent with the millimeter size inferred from spectral index analyses. We also discuss the possible contamination of self-scattering at long wavelengths as well as the effects of turbulent mixing.

12:00 → 12:30 Characterizing cosmic dust particles from photo-polarimetry. The IAA- Cosmic Dust Laboratory.: OLGA MUNOZ

Over the last ten years the cosmic dust laboratory (CoDuLab) has produced an important number of experimental phase functions (PF) and degree of linear polarization (DLP) curves for clouds of cosmic dust analogue particles. The experimental data are freely available at the Granada-Amsterdam Light Scattering database (www.iaa.es/scattering). The analogue samples comprise a wide range of sizes (sub-micron up to mm-sized grains), shapes, and compositions. In this talk I will discuss our current efforts to establish the link between dust physical properties (size, shape/structure, and composition) and the way they scatter light in all directions. From direct comparison of the experimental data with computations for homogeneous spherical particles I will show that the use of the spherical model for simulating the PF and DLP curves of irregular dust can produce dramatic errors in the retrieved composition and size of the scattering particles.

12:30 → 14:00 Lunch

14:00 → 14:30 The physico-chemical connection between nascent planets and their birth environment - An observational perspective in PDS 70: STEFANO FACCHINI

The large variety of observed planetary systems is rooted in the complex physical and chemical processes that lead to their formation. In the last few years, great observational and theoretical developments have dramatically improved our understanding of how forming planets are affected by and interact with their birth environments, the protoplanetary disks. As host to two accreting planets, PDS 70 provides a unique opportunity to probe how planets sculpt their hosting protoplanetary disk in its density and kinematical structure, to characterize the chemical complexity of atmosphere-forming material, and to directly observe the moon-forming potential of their circumplanetary disks. In this talk, I will present recent and new data of the PDS 70 system, showing new evidence of circumplanetary disks, of high C/O ratio gas in the proximity of the two planets, and new evidence of the mutual interactions between the accreting planets and their hosting disk.

14:30 → 15:30 WEEK DISCUSSION: Leader Testi/Guillet

lundi 24 mai

09:00 → 18:00 PUBLIC HOLIDAY

mardi 25 mai

11:00 → 11:30 New laboratory data for dust models: KARINE DEMYK

Cosmic dust models are key ingredients in modelling and advancing in our understanding of astrophysical environments as diverse as interstellar clouds, circumstellar enveloppes of evolved and young stars or protoplanetary disks. They consists of several dust populations having different compositions and size distributions. All include a population of silicate grains and most of them also include carbonaceous grains as well as a PAH component. The emission, absorption and scattering properties of these grain populations are calculated from their optical constants and fundamental properties which have various experimental, phenomenological or theoretical origins depending on the models. In this talk I will present new experimental data on the absorption opacity of silicate dust analogues and their related optical constants. I will also present preliminary results on PAHs obtained within the context of the LAIBrary project (Library of simulated AIB spectra) aiming at providing fundamental data needed to model their emission .

11:30 → 12:00 First MATISSE L-band observations of HD 179218. Is the inner 10 au region carbonaceous?: ALEXIS MATTER/ELENA KOKOULINA

Carbon is one of the most abundant components in the Universe. While silicates have been the main focus of solid phase studies in ProtoPlanetary Discs (PPDs), little is known about the solid carbon content especially in the planet-forming regions ( ~0.1 to 10 au). Fortunately, several refractory carbonaceous species present C-H bonds (like hydrogenated nano-diamond and amorphous carbon, Polycyclic Aromatic Hydrocarbons (PAHs)), which generate IR features that can be used to trace the solid carbon reservoirs. The new mid-infrared instrument MATISSE, installed at the Very Large Telescope Interferometer, can spatially resolve the inner regions (~1 to 10~au) of PPDs and locate, down to the au-scale, the emission coming from carbon grains. We present the first MATISSE L-band observations of the Herbig Ae star HD179218. Its disk exhibits an unusual extended inner emission up to 10 au, which could be due to carbonaceous species. We simultaneously modeled the SED and all the available interferometric data to provide a global view on the spatial structure of the inner disk region and give preliminary constraints on the location of the carbonaceous grain emitting region. Finally, in the perspective of upcoming MATISSE observations at higher spectral resolution we assess the feasibility of detailed characterization of the carbonaceous grain emission in the 1-10 au region.

12:00 → 12:30 The early phases of disk formation: the gas and dust story: UGO LEBREUILLY

Dust is an essential component of protoplanetary disks. The dust grains are the seeds of planet formation, they control the coupling with the magnetic field through the values of the non-ideal magnetohydrodynamics (MHD) resistivities and their continuum emission is extremely useful to observe star and disk forming regions. In the first part of this presentation, I will review recent results that we presented in Lebreuilly et al. 2020. In this work, we described in details the conditions for a gas and dust decoupling using the RAMSES code (Teyssier 2002) and its dust module (Lebreuilly et al., 2019). These conditions, when met, lead to the formation of protoplanetary disks that are initially significantly enriched in large dust grains. Protoplanetary disks and stars are not formed in isolation but rather in large turbulent clumps. To understand how the clump environment impacts the disk formation is crucial to determine their initial conditions. In that prospect, in the second part, I will introduce our new massive clump collapse simulations of 1000 solar mass gas-only clouds with and without non-ideal MHD (ambipolar diffusion) that aim to investigate protoplanetary disk formation within a self-consistent environment. These simulations, that resolve the disks up to the astronomical unit scale, allow us to obtain synthetic populations of early protoplanetary disks that can be compared with observed populations.

12:30 → 14:00 Lunch

14:00 → 14:30 Weighing planets and discs with ALMA: GIUSEPPE LODATO

The impact of ALMA in planet formation studies has been apparent since the discovery of the complex disc substructure, often made of rings and gaps in dust continuum images, that may be the signature of the presence of a planet embedded in the disc. Now, ALMA is revealing its full capabilities to work as a "planet detection machine", where the planet properties can be potentially constrained with high precision thanks to the study of the gas kinematics in the vicinity of the planet, that bears the imprint of the planet gravitational field. In addition, the high spectral and spatial resolution observations that are needed to this effect can bring further information on deviations from Keplerianity due to other sources, such as the disc’s own self-gravity. In this talk, (1) I will describe how to model semi-analytically the velocity perturbations induced by a planet in the gas, which is an essential ingredient to provide accurate fitting of the planet properties from gas kinematics and (2) I will describe our recent dynamical measurement of the disc mass in Elias 2-27 by using large scale deviations from Keplerianity in the gas rotation curve, confirming that the disc in this source is massive and is the likely responsible for the observed spiral structure in the dust continuum.

14:30 → 15:30 WEEK DISCUSSION: leader Commercon

mercredi 26 mai

11:30 → 12:00 Revisiting 3-µm water-ice feature in disk reflected light of the outer disk of HD 142527: RYO TAZAKI

Water ice is thought to be the most abundant volatile in a low-temperature region of protoplanetary disks. A promising tool to study water ice in disks is to observe its 3-µm feature, which is attributed to O-H vibration of water molecules in ice. The outer disk of HD 142527 is known to exhibit the 3 µm feature in disk reflected light. Honda et al. (2009) showed that dust particles should contain a significant amount of water ice to explain the observed ice feature. However, in the previous modelling, isotropic scattering of icy particles was assumed for simplicity and it is unclear how this assumption affects the ice abundance estimate. In this study, we perform 3D Monte Carlo radiative transfer simulations for the outer disk of HD 142527 and study the 3-µm ice feature in the disk reflected light spectra. As a result, we find that the isotropic scattering assumption leads to an overestimation of ice abundance for µm-sized grains, and therefore, the observed ice feature can be explained with much lower ice abundance than that inferred in the previous study. In addition, our results suggest that icy particles might be as large as 3 µm, indicating efficient vertical mixing in the disk. In the talk, we also discuss future prospects of water ice observations in disks with JWST.

12:00 → 12:30 Study of porosity in astrophysical ice analogs using ultrasonic propagation: SOFIA APARICIO, ITEFI

The chemistry expected to take place in astrophysical ice mantles exposed to radiation and cosmic rays, and also the physical processes such us desorption, must be influenced by the intrinsic ice properties. Among the physical properties of relevance are the ice density, the amorphous/crystalline ice structure, and the ice optical constants. We developed a method to measure the propagation of ultrasonic pulses through the ice, aiming to estimate the net porosity of ice samples grown under different conditions. The porosity of ice mantles in interstellar and circumstellar regions is a relevant and yet unknown ice property that affects the chemistry. Indeed, due to its large effective surface, a highly porous water-dominated ice is expected to enhance chemical reactions with other species and radicals hosted in the micropores upon energetic processing of the ice. Our experimental configuration and first results will be presented.

12:30 → 14:00 Lunch

14:00 → 14:30 Multiple stellar systems, discs & planets: NICOLAS CUELLO

What is the impact of stellar multiplicity on planet formation? This question is motivated by the fact that the process of stellar formation leads to a very high fraction of multiplicity. On top of this, planet formation occurs early on around young stellar objects. This leads to an unavoidable conclusion: protoplanetary discs are deeply affected by the presence of nearby stars. In this talk, we will first explore disc dynamics and planet evolution around binary, triple, and quadruple stellar systems – as opposed to single stars. Then, based on recent numerical works, we will briefly review some recent observations (mainly with ALMA & SPHERE) of multiple stellar systems with highly asymmetric discs. Finally, we will discuss the effects of stellar multiplicity on planet formation in terms of disc morphology, dust dynamics and planetary stability.

14:30 → 15:30 WEEK DISCUSSION: leader Cabrit

jeudi 27 mai

11:30 → 12:00 The B59’s Pipe Nebula Laboratory to study planet-forming disks: JM GIRART

The dense molecular cloud Barnard 59 is the only site of active star-formation in the overall quiescent Pipe nebula, a 10,000 solar mass quiescent dark cloud located at a distance of 163 pc. The core harbors a small cluster of low-mass YSOs first observed in mid-infrared bands with the Spitzer telescope. In this talk, following an introduction of the overall properties of the B59 region, I will present two very distinct and different planet forming disks. [BHB2007]-11 is the youngest stellar (binary) system in the region, classified as a Class I protostar. ALMA observations has revealed a complex and unexpected features around this binary. For example, an outflow launched at the putative centrifugal radius, at the edge of the circumbinary disk, and an intricate network of dusty filaments around the binary stars. [BHB2007]-1 is a flat spectrum YSO surrounded by a very young giant planet/brown dwarf embedded in the disk that surrounds the star. Evidence of accretion is seen at all scales, from the cloud to the disk and from the disk to the planet and star.

12:00 → 12:30 Impact of MHD winds on disk evolution: B. TABONE

Dust grains in disks orbiting nascent stars are the building blocks of planetesimals. The evolution of dust depends markedly on the global structure the disk (surface density profile, temperature) that is ultimately controlled by the transport of angular momentum and mass-loss processes. Recently, there has been a growing recognition that magnetic outflows launched from disks (’’MHD disk-winds’’) will have a crucial impact on disks and on the underlying dust evolution, by extracting angular momentum and creating substructures. However, the presence of MHD disk-winds remains an open question. The unique combination of sensitivity and angular resolution offered by ALMA and the future JWST is enabling us to conduct stringent tests on the presence of MHD disk-winds and inform dust evolution models. In this contribution, I will present our ongoing effort to assess the role of MHD disk-winds in disk evolution. I will review an ALMA study of the protostellar system HH212 down to 16 au scales that provides the most stringent observational test of MHD disk-winds to date. New observations of more evolved disks (Class II) will also be discussed. I will then put MHD disk-winds in the context of disk demographics as unveiled by recent ALMA and VLT- XSHOOTER surveys. I will show that wind-driven accretion can account for disk dispersal and the correlation between accretion rates and disk masses. This work is based on a simplified disk evolution model which can be used to study dust evolution and planet formation in the emerging paradigm of MHD disk-winds.

12:30 → 14:00 Lunch

14:00 → 14:30 Thermal and photon-induced desorption dependence on ice mantle composition and physical properties: GUILLERMO MUNOZ CARO

Energetic photons and ions impinging on dust grains can lead to desorption of ice molecules, and could therefore account for the observed gas phase abundances toward very cold regions. Several studies reproduced CO ice irradiation with UV in the laboratory because this molecule is not directly dissociated at photon energies below 11 eV, which leads to an efficient photodesorption that can be measured by the decrease of its infrared absorption band. The linear decrease of the CO photodesorption yield as a function of ice deposition temperature is intriguing and cannot be explained by variations in the ice amorphicity or density, since these physical properties only change during the onset of crystallization above 20 K. We will provide an alternative explanation for this behavior of the photodesorption. Other molecular ice components are, either efficiently photodissociated, or not active in the infrared: CH3OH, CO2, O2, CH4, NH3, etc. Their photon-induced desorption is two or more orders of magnitude lower than that of CO. Interestingly, some of the photoproducts in these experiments are found to desorb during irradiation. The desorption of photoproducts follows two different patterns: a) an increasing desorption up to a maximum as the concentration of the product grows in the ice bulk, and b) a constant desorption that results from photochemical processes on the ice surface that we refer to as ¨photochemidesorption¨, which leads to the desorption of fragments or molecules due to their excess energy of formation. In our presentation we will discuss the intriguing CO photodesorption dependence on the physical ice properties, and the different desorption mechanisms of large photoproducts like C2H6 and C3H8, which may open a route toward the desorption of other COMs in cold regions

14:30 → 15:30 WEEK DISCUSSION: leader Louvet

vendredi 28 mai

11:30 → 12:00 Temperature structure of young disks: probing the initial physical and chemical structure of planet-forming regions: DANIEL HARSONO

The physical structure of disks during the early stages of their formation is crucial for understanding the accretion process and planet formation. However, the temperature structure of young disks is still poorly understood. The temperature structure of young disks is an important parameter that is connected to the accretion rate. Furthermore, it also sets the composition of the planet-forming material. In this talk, I will present the models and observational results of the temperature structure of young disks.

12:00 → 12:30 Organic-rich xenolithic clast in the Zag meteorite: A possible evidence for the giant planet migrations: YOKO KEBUKAWA

12:30 → 14:00 Lunch

14:00 → 14:30 Steady-state MRI-driven Accretion in Protoplanetary Disks: TIMMY DELAGE

"Protoplanetary disks are weakly ionized environments where the non-ideal MHD effects play an important role in the gas dynamics. As such, the magnetorotational instability (MRI) cannot operate everywhere and generate a fully turbulent disk. Instead, a so-called dead zone naturally occurs, where the turbulence level is low and dominated by non-MRI stresses (e.g. hydrodynamic instabilities). The most promising location of a dead zone is its outer edge. Previous studies have shown that the dead zone outer edge can efficiently trap dust particles, hence being a possible explanation for the origin of the observed disk sub-structures. In order to properly assess the dead zone mechanism as a potential candidate, gas/dust evolution and non-ideal MHD calculations must be coupled. The first step towards this goal is to obtain an appropriate parameter encoding the disk turbulence level called the
turbulent parameter alpha. In this talk, I will present a 1+1D magnetically-driven disk accretion model that self-consistently determine the turbulent alpha-parameter from detailed considerations of the MRI and non-ideal MHD effects (Ohmic resistivity and Ambipolar diffusion) -given stellar properties (mass and luminosity), disk mass and dust properties. The main processes we include are: (1) irradiation from the forming star; (2) dust settling; (3) ionization from stellar X-rays, galactic cosmic rays and the decay of short/long-lived radionuclides; (4) disk chemistry; (5) turbulence driven by the MRI accretion and hydrodynamics instabilities. Particularly, we apply our framework to investigate the outer structure of steady-state viscously accreting protoplanetary disks, and determine what are the key parameters at play by conducting an exhaustive parameter study."

14:30 → 15:30 WEEK DISCUSSION: leader Morbidelli