From Disk Formation to Exoplanetary Systems

Monday Sep 22, 2025, 9:00 AM → 7:30 PM Europe/Berlin

Eridanus Auditorium (ESO Headquarters)

As part of the ORIGINS Cluster, we are organizing a 1-day session on September 22nd, 2025 at the ESO HQ on topics that span from the formation of protoplanetary disks to their evolution, to planet formation, all the way to the detection and characterization of exoplanetary systems.

We invite you to register for the workshop and optionally submit an abstract for a contributed talk. Please complete your registration by July 18th, 2025.

Morning Session

1 Registration & Welcome

2 Characterization of the Carina OB1 association

The Carina OB1 association is one of the most massive, well-studied star-forming regions in our Galaxy, which is the kind of environment where most of the planets in our Galaxy are formed. We aim to characterize the association's stellar population as stellar clusters and high-mass stars heavily influence planets and disks. We therefore used the Gaia DR3 catalog to identify clusters and their precise position and extent, and to search for the distributed population of high-mass stars in Car OB1. We find 15 stellar groups and clusters and compile a catalog of 1374 high-mass stars, including 604 new OB candidates, in Car OB1. Extrapolating from our high-mass star catalog using the Kroupa IMF, we obtain a total number of $8\times 10^4$ stars for the entire association. We will also give a brief outlook on future disk research in Car OB1, as highly irradiated disks in the most massive cluster in Car OB1, Trumpler 14, are currently being observed with JWST as a part of the XUE collaboration.

Speaker: Christiane Göppl

3 Observing proplyds with MUSE

In clusters with OB-type stars, UV radiation affects the evolution of protoplanetary disks via external photoevaporation. The resulting depletion of disks can be studied in resolved observations of proplyds, where neutral gas is outflowing from the disk and becomes photoionized as it expands and interacts with stellar UV radiation. VLT/MUSE allows us to characterize proplyds in a wealth of emission lines. I will present results based on the IFU data of 12 proplyds in the Orion Nebula Cluster acquired with MUSE in Narrow Field Mode. We detect a forbidden carbon emission line at 8727 Å in all proplyds, and compare the spatial location of the emission traced by MUSE with the ALMA Band 7 continuum disk emission. We show the [CI] 8727 Å line to trace the surface of the disk and the base of the externally photoevaporative wind. We measure the line ratios of selected emission lines, and find them to be low for neutral species and high in highly-ionized species, agreeing with the trends observed in the sigma-Orionis Cluster. The comprehensive view of these systems opens the scene to study more distant and massive star-forming regions.

Speaker: Mari-Liis Aru

4 Magnetospheric accretion onto Herbig Ae/Be stars

Herbig Ae/Be stars are surrounded by active accretion disks, as evidenced from excess emission seen in various wavelength regions. From studies of the Zeeman effect in polarimetric spectra of these PMS stars, it is clear that HAeBes host dipolar magnetic fields, which are about a magnitude weaker than those in their lower mass counterparts, the T Tauri stars.

While these weaker magnetic fields have generally been ignored in the accretion processes of HAeBes, there is evidence for magnetospheric interaction between the the disk and the magnetic star. To understand the complex magnetospheric processes taking place in Herbig Ae/Be stars, it is important to characterize their magnetospheres, which extend outward into the surrounding environment.

In my talk, I will present our results from recent studies of magnetic fields and the magnetospheric structures in a few Herbig Ae/Be stars.

Speaker: Markus Schöller (European Southern Observatory)

5 Tracing Young binaries with Multi-wavelength Approach

Accreting binary systems exhibit complex, multi-wavelength variability shaped by their interactions with circumstellar and circumbinary material. DQ Tau, highly eccentric (e = 0.6), equal-mass binary with a 15.7-day period, is a prime target to investigate accretion physics and disk structure in young binaries. With its short orbital period, DQ Tau owns three accretion disks and strongly pulsed accretion near periastron.
We present a multi-epoch spectroscopic campaign using VLT/UVES and X-Shooter, alongside LCO u′-band photometry from a coordinated JWST and ground-based monitoring program. Applying the broadening function (BF) technique, we disentangle radial velocities (RVs) of both stellar components and trace flux variations linked to orbital phase and veiling. Spectral disentangling carried out on emission lines allows us to study the individual mass accretion rates across 9 orbital cycles, showing nearly two orders of magnitude variability near periastron. Understanding the orbital and accretion behavior of DQ Tau is critical for interpreting simultaneous JWST data and its influence on the inner disk properties.
From the well-characterised case of DQ Tau, we venture into a population of transition disks whose large cavities, shadowed outer disks, and astrometric signal hint at unseen companions. The initial analysis of the ESPRESSO/VLT monitoring over 3 years reveals dual RV signatures in some of these targets, suggesting hidden companions as the origin of cavities.

Speaker: Hala Alqubelat (European Southern Observatory)

6 Formation of protostars and their accretion disks in the turbulent and magnetized interstellar medium

While recent observations of young protostellar disks have revealed much about their structure, their formation process from molecular cloud cores and subsequent evolution remains relatively poorly understood. In particular, the role of the magnetic field in regulating the angular momentum budget of the system is a central issue. In this talk, zoom-in simulations from a turbulent interstellar medium to protostars are presented, with a spatial range spanning more than 10 orders of magnitude. Using a newly developed implementation of non-ideal magnetohydrodynamics (MHD) for the moving-mesh code AREPO, we compare models without magnetic fields, with ideal MHD and finally including ambipolar diffusion. While disks of several 10s of astronomical units readily form without magnetic fields, ideal MHD strongly suppresses disk formation through magnetic braking and outflows. Non-ideal MHD does in a subset of cases lead to disk formation, but these disks are distinct from those without magnetic fields in size and structure. We show that where comparison can be made, our results are consistent with earlier studies of isolated cloud core collapse. We conclude that non-ideal MHD effects are prominent in the disk formation process even when fully self-consistent turbulent initial conditions are used, and their importance is not limited to idealized collapse scenarios. As such, both realistic initial conditions and the use of an appropriate magnetic field model are crucial in modeling the formation of protostellar disks. Finally, the effects of radiative transfer on disk structure and the impact of magnetic fields in the formation of multiples are briefly discussed.

Speaker: Alexander Mayer (Max-Planck-Institute for Astrophysics)

10:30 AM Cofee Break

7 Disk properties during the earliest stages of star and planet formation

Characterizing the physical conditions of disks surrounding young protostars that are still actively accreting from their surroundings is crucial to understanding the mass assembly process of stars and the mechanisms for early planet formation. While the majority of theoretical investigations into the first steps to form planetesimals are still using physical properties akin to more evolved disks past the main accretion phase, it is expected that the physical properties in much younger disks will be different. I will present ALMA observations with a resolution of 7 au towards young protostellar disks, with various morphologies and multiplicities. Using a multi-wavelength approach, we find that these disks are very optically thick, even at 3 mm. These high optical depths can help hiding the presence of early’ gaps’ related to the planet formation process, push the disk masses beyond the threshold for gravitational instability and make the disks appear brighter than their more evolved counterparts. The observations are also questioning the common assumption that star irradiation alone is the main mechanism controlling the disk temperature. Instead, the observed high temperatures suggest that some young disks are also heated due to dissipative processes such as accretion and shocks.

Speaker: Maria Jose Maureira (MPE)

8 The origin of chemical complexity: in the earth of young forming planetary system.

The earliest phases of planetary system formation are marked by a fascinating and intricate chemistry, with a high abundance of prebiotic molecules detected in protostellar environments. This chemical complexity serves as a crucial diagnostic tool to understand the underlying physical processes shaping these nascent systems, and to probe the chemical evolution from prestellar core to more evolved disks.
Indeed, part of the chemical processing happening during the prestellar and protostellar phase may affect later stages of evolution. For example, the observed diversity in the large variety of exoplanets detected so far, can be the result of a diversity already present at the early stages of their formation.
One of the striking results of the past years is the chemical diversity revealed in Sun-like protostars. Indeed, from a chemical point of view protostars differs from each other: some of them show millimetric molecular spectra rich in interstellar organic complex molecules (the so called hot corinos), and some others are enriched of unsaturated small carbon chains (the so called WCCC sources). The origin of this diversity is still unclear, as well as its impact on the chemical composition of future forming planets.
Additionally, to fully characterize these deeply embedded objects, combining millimeter and centimeter wavelength observations is crucial to account for the effects of dust opacity. This can significantly impact the derived abundances and temperatures, with important implications not only for the physical and chemical structure of protostars, but also for linking early-stage chemistry to the composition inherited by forming planets.

Speaker: Marta De Simone

9 On the use of Gaia astrometry to indentify companions in forming stars

I will show how to use Gaia astrometry to indentify binaries and companions in forming stars. I will exemplify the power of this technique with a few science cases, from newly identified protoplanets within the gaps and cavities of protoplanetary disks to a reassesment of the multiplicity of the populations of circumbinary and transition disks. I will conclude looking forward to the upcoming Gaia DR4 and the revolution it will bring for multiplicity analyses, once all individual Gaia epochs are published.

Speaker: Miguel Vioque (miguel.vioque@eso.org)

10 Characterizing the dust in the outer regions of protoplanetary disks with ALMA

The dust mass budget of protoplanetary disks plays an important role in planet formation. However, ALMA surveys often underestimate disk masses as many disks have extended low surface-brightness regions at hundreds of au that fall below ALMA's sensitivity limits. This may contribute to the mass-budget problem where exoplanetary systems appear to be more massive than disks. In this talk, I will present my work on TW Hya where we used both image-plane retrieval as well as visibility-plane modeling on ALMA observations, to discover a faint outer ring at multiple millimeter wavelengths that has a spectral index similar to that of the ISM. We extend this study to other disks that exhibit extended emission and could potentially host a dust mass reservoir. We model the emission properties while exploring how grain composition and porosity affects the derived mass. Furthermore, investigating their surface density and particle size distribution may allow us to shed light on their origin - whether it is primordial or replenished by late infall.

Speaker: Sreejita Das (European Southern Observatory)

11 Understanding dust evolution in protoplanetary disks

Dust plays a fundamental role in the formation of planets, acting as the primary building block from which planetary systems emerge. To understand the origins and diversity of the planetary systems observed throughout the galaxy, including our own Solar System, it is essential to investigate how micron-sized, amorphous dust grains found in the interstellar medium are transformed into the high-porosity (70–95%) kilometer-sized bodies observed in the form of comets in our solar system.

The key to understand dust reprocessing and planet formation is characterizing the dust content of the cradles of protoplanets: the circumstellar disks. By estimating both the amount and composition of dust in these systems, we can constrain the conditions under which planet formation occurs, and ultimately address the key questions of where, how, and when planets form.

In my talk, I will present the state-of-the-art technique for dust characterization of disks: millimeter spectral energy distribution analysis. I will discuss the dust properties that can be derived from this method, such as dust mass, grain size distribution, and composition, and its limitations. Particularly, I will illustrate on simulated observations how the current angular resolution and sensitivity of ALMA and the VLA affect this analysis. I will also explore how the ALMA's Wideband Sensitivity Upgrade and the next-generation VLA are expected to mitigate these limitations.

Finally, I will present new high-resolution, high-sensitivity VLA observations of the well-known protoplanetary disk GM Aurigae. I will comment on the disk properties that can be robustly constrained from these data. By carefully combining observations with modeling and simulations, we can refine our understanding of how planetary systems originate from the dusty environments surrounding young stars.

Speaker: Elena Viscardi (ESO)

12:00 PM Lunch Break

Afternoon Session

12 A closer look at the building blocks of planetesimals: characterizing the dust content of protoplanetary disks

The dust content of protoplanetary disks plays a crucial role in the planet formation process. The key ingredients are not only the total budget of solid mass and the dust particle size distribution, but also how these are distributed throughout the protoplanetary disk. Characterizing the dust surface density, particle properties, and size distribution within the disk and its substructures is, therefore, critical in order to shed light on how and where in the disk planetesimals might form.
In this talk I will show recent detailed studies of various protoplanetary disks that we have performed using multi-wavelength high-resolution observations taken with ALMA and VLA. One of our main results is that the emission from most of the disks’ substructures is optically thick even up to 3 mm, implying that flux-based dust mass measurements can be significantly underestimated. These high optical depths can also severely limit our ability to characterize the dust content of disks, especially in the inner tens of au where most planets are thought to be formed, including our own Solar System. I will discuss how we can circumvent these issues by observing at longer wavelengths. I will also talk about some of our recent efforts to observationally constrain other dust grain properties in disks such as the grain composition, porosity, and fragility.

Speaker: Enrique Macias (ESO)

13 Evidence for Ongoing Planetesimal Formation in Protoplanetary Disks

High-resolution ALMA observations of protoplanetary disks commonly reveal multiple narrow rings. Surprisingly, many of these rings exhibit similar moderate optical depths (τ ≃ 0.2–0.5 at millimeter wavelengths), despite substantial variation in disk environments — a puzzling uniformity that hints at some underlying unknown effect regulating dust physics.

We propose that this “optical depth fine‑tuning” arises naturally from ongoing planetesimal formation via streaming instability. Using DustPy, our open-source Python package for gas and dust evolution in protoplanetary disks, we simulate radial drift, grain growth, fragmentation, and the conversion of pebbles into planetesimals once midplane dust-to-gas ratios exceed unity. Our simulations consistently reproduce ring optical depths in the observed range by converting excess dust into “invisible” planetesimals — without arbitrary opacity adjustments. These results support the hypothesis that disk rings regulate their optical depth through active planetesimal formation.

Speaker: Sebastian Stammler (LMU)

14 Spirals, rings, and vortices shaped by shadows in protoplanetary disks

Numerous protoplanetary disks exhibit shadows in scattered light observations. These shadows are typically cast by misaligned inner disks and are associated with observable structures in the outer disk such as bright arcs and spirals. Investigating the dynamics of the shadowed outer disk is therefore essential in understanding the formation and evolution of these structures. We carry out twodimensional radiation hydrodynamics simulations that include radiative diffusion and dust–gas dynamics to study the formation of substructure in shadowed disks. We find that spiral arms are launched at shadow edges, permeating the entire disk. The local dissipation of these spirals results in an angular momentum flux, opening multiple gaps and leading to a series of concentric, regularly-spaced rings. We find that ring formation is favored in weakly turbulent disks where dust growth is taking place. These conditions are met for typical class-II disks, in which bright rings should form well within a fraction of their lifetime (∼0.1–0.2 Myr). For hotter disks gap opening is more efficient, such that the gap edges quickly collapse into vortices that can appear as bright arcs in continuum emission before decaying into rings or merging into massive, long-lived structures. Synthetic observations show that these structures should be observable in scattered light and millimeter continuum emission, providing a new way to probe the presence of substructure in protoplanetary disks. Our results suggest that the formation of rings and gaps is a common process in shadowed disks, and can explain the rich radial substructure observed in several protoplanetary disks.

Speaker: Alexandros Ziampras (LMU Munich)

15 Not Your Typical Disk: ALMA unveils an expanding, ring-shaped structure in G23.6

The formation of high-mass stars remains one of the key open questions in astrophysics. While structures familiar from low-mass star formation such as outflows, jets, and rotating centroids have been observed in massive star-forming regions, detailed studies at spatial scales of a few hundred AU are still rare and limited to only a handful of sources.
Recent ALMA observations of the high-mass protostellar object G23.6 have revealed a remarkable ring-shaped circumstellar disk with an inner cavity, the first of its kind to be resolved with this morphology at such small scales. Proper motion measurements of methanol masers trace the ring's expansion away from the central source. Strikingly, the ring is rich in complex organic molecules, while its centre appears depleted of molecular gas and dust, except for localized emission from sulfur-bearing species. These may trace shocks at the disk-envelope interface, potentially driven by infall or outflows. A mild velocity gradient across the ring in multiple molecular lines is consistent with a slow component of rotation.
In this presentation, I will explore the unique morphology and kinematics of this circumstellar ring, present detailed analyses of its molecular content, and discuss its implications for models of massive star formation.

Speaker: Katharina Immer (ESO)

16 Compact or large? CO observations of the faintest planet-forming disks.

Planet-forming disks observed by ALMA surveys often exhibit surprisingly faint continuum and CO emission, raising doubts about whether these disks contain enough material to account for the known exoplanet population. Despite this, the fainter end of the disk population - which shows compact, unresolved continuum emission and non-detections in CO isotopologues - has received little detailed investigation. It remains unclear whether this is due to faint but spatially extended emission or intrinsically compact disk structures. Distinguishing between these scenarios is crucial: if such disks are indeed compact, including their gaseous components, and optically thick, their inner regions could harbour significant reservoirs of material, potentially capable of forming gas giants within Jupiter's orbital radius. In my talk, I present new ALMA data that target 13CO(3-2) and 12CO(3-2)lines in 18CO-faint Lupus disks, probing the gaseous component of the faintest planet-forming disks. The results confirm that these disks are optically thick and potentially radially compact, therefore we could imply a substantial planet-forming capacity within 10 au in a significant fraction of Lupus disks. Furthermore, these disks challenge widely accepted theories of disk evolution, such as viscous evolution and MHD-driven processes, which cannot account for such small outer radii. The absence of environmental factors in Lupus suggests that compact disks may be a more common outcome of disk evolution than previously assumed. By investigating disks in environments where external effects are negligible, we can refine our understanding of intrinsic disk evolution processes and reassess their role in setting the initial conditions for planet formation.

Speaker: Giulia Ricciardi (ESO)

2:45 PM Coffee Break

17 Icy content of planet forming material with JWST

Recent observations by ALMA suggest that planets may begin forming much earlier in the lifecycle of stellar systems than previously thought, in the protostellar systems. These systems are abundant in icy and gaseous material which can contribute to the planetesimals forming there. I will present JWST results of the icy content of these systems, particularly multiple new molecular detections that we did not have access to with previous telescopes.

Speaker: Pooneh Nazari (ESO)

18 Characterization of protoplanetary disks near and a far: a complementary perspective

Given the variety of properties found in planetary systems in our Galaxy, we must analyse general disk and host star properties measured in a large statistical sample of systems at different evolutionary stages and environments. Disks in nearby regions evolve differently than disks in highly irradiated environments. Since the majority of (exo)planet host stars (including our Solar System) form in dense and massive stellar clusters in which the presence of OB-type stars dominates the radiation field, disk evolution studies must consider internal as well as external factors shaping the evolutionary path of protoplanetary disks in a complementary way.

During this talk, I will focus first on how the most “typical” disks in nearby regions look in dust continuum emission. Then, I will contrast these results with those found in a more representative cluster in Orion.

I will show the results of dust continuum analysis of 80 disks in 4 nearby star-forming regions as part of the DECO ALMA large program. I will present dust disk size estimates and dust morphology identification results obtained through visibility fitting with GALARIO. In contrast, I will also describe how disk evolution is affected by the feedback from massive OB stars in more distant clusters, focusing on the more representative sigma-Orionis cluster, where its innermost regions are clearly affected by external irradiation from the massive system sigma-Ori, suggesting a coevolution of internal and external winds in these disks.

Speaker: Karina Mauco

19 Characterising the carbon chemistry in gas giants near the snowline

Direct observations of substellar companions are ideally suited to study young giant planets and brown dwarfs during or shortly after their formation. As such, this unique class of objects provides valuable insights into planet formation processes and the imprints they leave on the chemical composition and atmospheric properties of young companions. However, the traditional population of directly-imaged giant planets and brown dwarfs resides at wide (>20 au) separations from the host star, where classical high-contrast imagers are able to detect them. Recently, long-baseline interferometry has opened up the direct detection of substellar companions on Solar System like scales, down to a few au from the star. This enables studying young giant planets where they are expected to form most frequently, and removes possible biases introduced by planet migration and scattering processes. Novel data reduction approaches for JWST making use of machine learning techniques now enable the study of the same objects at au separations with JWST interferometry, providing new constraints on CO and CO2 abundance in the mid-infrared (3-5 micron). By combining JWST and GRAVITY, the atmospheres of gas giants near the snowline can now be studied at an unparalleled precision, yielding not only constraints on the carbon chemistry, but also the formation history of these objects if combined with dynamical masses from Gaia DR4 in the near future.

Speaker: Jens Kammerer (ESO)

20 Isotopologue chemistry imprinted on young planets

We have long been interested in the chemical link between protoplanetary disks and planetary atmospheres. But this has largely been limited to the most abundant isotopes of elements like oxygen and carbon. More recent observational efforts have begun to identify the precence of less abundant isotopologues like $^{13}$CO in the atmospheres of giant planets and sub-stellar objects. Here I will outline some preliminary work linking isotopologue chemistry in disks through planet formation models to these detections, and outline some recent observational efforts going on at the USM.

Speaker: Alex Cridland (Universitäts-Sternwarte Munich (USM), LMU)

21 Is the high-energy environment of K2-18b special?

The high-energy environments of host stars can shape the chemistry of exoplanet atmospheres. In nearby benchmark systems, hosting rocky to sub-Neptunian planets, we focus on the impact on biosignature gases such as oxygen, methane, and carbon dioxide. With new data from Chandra, eROSITA and XMM-Newton, we study the X-ray flux variability on timescales of days to years. Using a Bayesian framework to model multi-temperature coronal plasmas and integrating it with the VPLanet and KOMPOT modeling packages, we examine how XUV-driven escape affects atmospheric composition and thermal structure. K2-18b's atmosphere benefits from an exceptionally low level of XUV irradiation. Looking forward, we discuss our observational strategy aimed at characterizing sub-Neptune exoplanet host stars and detecting atmospheric biosignatures.

Speaker: Surangkhana Rukdee (MPE)

22 Discussion

23 Closing Remarks