How to cite: Kim, M. and Roccatagliata, V.: An imprint of low-mass companions in the substructures of debris disks, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-386, https://doi.org/10.5194/epsc-dps2025-386, 2025.

Although it is thought that the grinding down of planetesimals sustain the dust we see in debris disks, the occurrence rate and detectability of such collisions is not well understood. Beta Pictoris is an archetypal debris disk system whose proximity, brightness, and planetary system offers a unique opportunity to study the dynamical evolution of young planetary systems. We present new, multi-epoch imaging of the Beta Pictoris debris disk in scattered light with HST/STIS. We present the highest precision, longest baseline surface brightness measurement variations from 1997 to 2025. Our measurement baseline, combined with Beta Pic b’s 20 year orbital period, allows us to test model predictions of planet-disk interactions in debris disks. On the other hand the surface brightness variation measurements of the high SNR, outer regions of the disk (50-200 au) allowed us to search for signs of recent collisional remnants and place constraints on the minimum mass collisional progenitor we are sensitive to with regular HST/STIS monitoring. We additionally present new theoretical work on the rate and probability of massive planetesimal collisions in debris disks. By varying disk parameters, we are able to provide a collision rate for a range progenitor sizes, which is then compared to observational evidence of collisions in debris disks like Fomalhaut and Beta Pic. Finally, using a combination of observational and theoretical constraints, we provide monitoring guidance on cadence and targets for HST and JWST.

How to cite: Avsar, A., Wagner, K., and Apai, D.: Observational and Theoretical Constraints on the Detectability and Occurrence Rate of Massive Collisions in the Beta Pictoris System, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1139, https://doi.org/10.5194/epsc-dps2025-1139, 2025.

A subset of debris disks are bright and show evidence of variability on short timescales, flux increasing or decreasing over months/years and in some cases oscillations on timescales of days (e.g. Su et al., 2019). These extreme debris disk phenomena are thought to be the result of energetic collisions between growing planetary bodies. These collisions can produce ejecta with narrow size distributions (Benz et al., 2007). The ejecta from such collisions can therefore be processed, thereby changing the population of grains, on much shorter timescales than traditional debris disks (Meng et al., 2014).

Extreme debris disks thus provide a key window into planet formation, but connecting the observed properties to the collisions that caused them is challenging. Much progress has been made in understanding how impact ejecta produces the complex signals observed (e.g. Watt et al., 2021); but there is currently no reliable way to relate the observed dust to the size of the impacting bodies. Typically, the inferred mass of dust is converted to a body size assuming the entire mass of the body was turned into dust. A collision both vaporising and ejecting the entire mass of a small body is, however, unlikely. High velocity planetary impacts have sufficient energy to cause shock-induced vaporisation of both water ice and silicates (Carter & Stewart, 2020; Davies et al, 2020), but most previous studies of impacts have ignored the effects of vaporisation. The masses of vaporised ejecta produced by collisions are thus poorly constrained. Vaporisation during planetary impacts is key to determining the sizes of ejected material. Understanding these collisions is essential for relating the observed signals from extreme debris disks to the impacts that caused them.

We present new, high resolution hydrodynamic simulations of planetary impacts designed to explore and quantify vapour production and the mass and state of ejecta. Vaporised ejecta is produced across a wide range of colliding masses and impact parameters. We derive a relation between the impact energy and the mass of vaporised ejecta that could be observed in young exoplanetary systems. By assuming a reasonable maximum impact velocity, the kinetic energy can be related to the minimum mass of the colliding planetary bodies. The emission observed from an extreme debris disk can thus be linked directly to the likely planetary collision that caused it.

How to cite: Carter, P. and Leinhardt, Z.: Identifying the collisions that make extreme debris disks, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-720, https://doi.org/10.5194/epsc-dps2025-720, 2025.

Disc instability remains the leading formation pathway for some of the observed giant planets. In particular, this model can more naturally explain giant planets at large separation, giant planets around M stars, and very young giant planets. However, there are still many open questions regarding this formation mechanism, and the expected population of planets is currently unknown. We developed a comprehensive model for the formation of a star-and-disc system through the collapse of a molecular cloud core and its evolution until disc dispersal and beyond. The model includes the potential fragmentation of the disc as well as the subsequent evolution of any fragments. We apply the model to perform a population synthesis in the disc instability paradigm (DIPSY). We will present the results of the baseline population and discuss the emerging population of companions around different types of stars. We find that, while fragmentation (the formation of bound clumps of gas in the disc, a necessary condition for planet formation in the disc instability model) may only happen in a minority of systems, it often leads to the formation of at least one companion when it does. The inferred population of companions spans a large range of masses, from the planetary to the stellar regime. The figure shows the result of the baseline calculation: the mass-distance diagram for 100’000 systems after 100 Myr. The final host star mass is given as colour code. The results of the population synthesis will provide hints both for the theoretical study of planet formation (e.g. hydrodynamic simulations) and future observational surveys of companions. DIPSY contributes to our understanding of planet formation irrespective of the formation model.

How to cite: Schib, O., Mordasini, C., Helled, R., and Emsenhuber, A.: DIPSY: A New Disc Instability Population Synthesis, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1763, https://doi.org/10.5194/epsc-dps2025-1763, 2025.

Introduction: The formation of planetesimals within a protoplanetary disk is strongly influenced by the collision and eventual aggregation of nano- and micro-scale dust particles (1). This granular collision process is most often modelled using Johnson-Kendall-Roberts (JKR) contact models, a well-established theoretical approach that determines the sticking, bouncing and aggregation of colliding grains. The surface free energy (SFE) is a crucial physical input to this model, governing the properties of dust grains at their interfaces. The SFE is a measure of the energy difference between a free surface and the bulk of material.  Particle surfaces with high SFE  are more likely to adhere strongly to each other, promoting  particle coagulation and facilitating the growth of larger bodies. In contrast, particle surfaces with low SFE adhere weakly, making it more difficult for particles to aggregate.

While this value is a key input into JKR models, it is not well understood in the complete protoplanetary disk regime. Previous experimental studies on SFEs for silica have measured values ranging from 0.02–2.5 J m^-2, over two orders of magnitude in difference (2). These results are typically limited to specific temperatures and do not consider the complex minerals beyond SiO₂ likely to be found in natural dust particles during collisions. As an alternative, molecular dynamics (MD) modelling can be used to study these surfaces on the atomic scale, allowing for energy differences between bulk and surfaces to be calculated as a function of temperature for different minerals. While research has been conducted using MD for SFEs, results are needed for the temperatures, background gas properties, and mineral types important in protoplanetary disks. These mineral-specific values are essential for models of planet formation and disk evolution, while also influencing our understanding of the chemical processes occurring in the early solar system.

Methodology: In this study, we use MD simulations to study the SFEs of silica, albite, and anorthite. Silica is chosen as it is a commonly studied mineral both theoretically and experimentally. Albite and anorthite were chosen as they are the two endmembers in the plagioclase feldspar family, thought to be abundant on many celestial bodies. We use a ReaxFF potential to model all interactions, allowing for dynamic bond formation and, for future studies, chemical reactions. For each mineral we first calculate the potential energy of the bulk periodic sample. We then open a surface to vacuum, equilibrate the sample at the desired temperature, and calculate the subsequent (PE) of the surface. The SFE is then calculated as the energy difference per unit area of a periodic bulk sample and its corresponding surface divided by the area of the surface. We simulate SFEs for 30K, 100K, 300K, and 700K, a range of temperatures expected to be found at various radii within protoplanetary disks.

Results:  Table 1 displays the equilibrated SFE for each mineral type at the different simulated temperatures.

For all temperatures silica has the highest SFE, followed by either albite or anorthite, suggesting that approximating grains as a simple silica structure may overestimate the SFE. In all cases the SFE decreases with temperature, potentially due to the increased atomic disorder with temperature reducing the energy needed to form a surface. For example, as temperature is increased from 30K to 700K the silica SFE is reduced by a factor of ~1.5. It is therefore important to account for specific temperatures within the disk when modelling grain interactions. These results suggest that a distribution of SFEs with temperature may be a more accurate approach. We can incorporate these different SFEs into various JKR relationships to show the effect on contact area, threshold velocity and pulling-off force.

In general, the SFEs at all temperatures are 1–2 orders of magnitude higher than commonly reported experimental values, which typically range from 0.02-0.03 J m^-2 (3-4). Results do however agree with limited MD simulations for the SFE of SiO₂ using different interatomic potentials (1). This discrepancy between experiment and theory may occur because experimental substrates are often studied at room temperature as surfaces that, when exposed to the ambient terrestrial environment, are likely to be hydroxylated and/or water passivated. This passivation can terminate free O bonds on the surface, potentially significantly influencing the energy of the surface. Therefore, if grains in protoplanetary disks are clean, as could be found at higher temperatures closer to the star, they will collide with a significantly different behavior than would be predicted using these experimental values. As such, SFEs need to be better quantified as a for both clean and covered surfaces as function of mineral type and temperature.  Here we provide a comprehensive set of simulations for clean surfaces in a true vaccum.

These novel results highlight the key role MD simulations can play in better understanding SFEs for grain contact modelling. SFEs are shown to be temperature and mineral specific, and likely highly sensitive to H or H₂O in the environment . These “clean surface” MD-derived values may be more appropriate than the comparatively lower experimental values when collisions occur in regions of the disk where water/H is less likely to adsorb.  Further work is required to quantify the influence of coverage along with the effects of amorphization.

References:

1. Kimura, K. Wada, H. Senshu and H. Kobayashi, Astrophys. J., 2015, 812, 67.

2. Blum, Res. Astron. Astrophys., 2010, 10, 1199.

3. Blum and G. Wurm, Icarus, 2000, 143(1), 138-146.

4. Kendall, N. M. Alford, and J. D. Birchall, Nature, 1987(London) 352, 794.

How to cite: Morrissey, L., Ebel, D., Eriksson, L., Huang, Z., Roy, J. L., Mac Low, M. M., and Pfeil, T.: Dust Collisions in the Protoplanetary Disk: Atomic Simulations to Better Understand the Surface Free Energy , EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-344, https://doi.org/10.5194/epsc-dps2025-344, 2025.

Context. Angular differential imaging (ADI), widely used in ground-based high-contrast imaging, often distorts extended emission such as protoplanetary disks. This hampers efforts to jointly study circumstellar disks and embedded protoplanets, particularly in systems like PDS 70, Lk Ca 15, and HD 163296, where disk substructures and planet formation are closely intertwined.

Aims. Our goal is to recover unbiased photometry and morphology of both disks and planets in these systems, free from self-subtraction artifacts introduced by ADI. This allows for a more accurate study of disk structure, grain properties, and potential dynamical interactions between planets and their natal environments. We also search for additional substellar companions at separations beyond the known planets.

Methods. We analyze SPHERE YJHK-band imaging, polarimetry, and integral field spectroscopy using reference star differential imaging (star-hopping) to preserve extended emission. Submillimeter ALMA data are included to constrain the disk structure and dust distribution. Radiative transfer modeling with RADMC-3D is used to interpret both scattered light and thermal emission, matching the observations in both total and polarized intensity. We also extract spatially resolved spectra of point sources and disk regions for comparative analysis.

How to cite: Wahhaj, Z.: Protoplanetary disks unveiled by star-hopping: Total intensity, polarimetry, and millimeter imaging modeled in concert, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-335, https://doi.org/10.5194/epsc-dps2025-335, 2025.

Among the variety of structures that can be observed at millimeter and sub-millimeter wavelength within disks, some present an inner cavity depleted from gas and dust. Such disks are called transitional disks (TDs). Cavities, are generally attributed to the formation and evolution of one or more giant planets (as it is the case for PDS 70), severing the connection between the outer and inner disks, which is then rapidly depleted by accretion onto the star. At the same time, these planets are modifying the disk gas pressure profile leading to the creation of a pressure trap and, consequently, a ring-like structure in the dust distribution, as large grains are confined as they drift in from the outer disk. This scenario, thus implies that the planets inside the ring greatly stops the exchange  of pebbles between the outer and the inner part of the disk. Even though, observations show that material continues to pass through the planet to the star, the stellar mass accretion in TDs is lower than for full disks of same age or mass. On top of it, since large grains are trapped within the ring, only small grains and gas can filtrate through the cavity, failing to fully explain the large amount of material needed by the central star. As a result, within the inner cavity, no significant dust emission at (sub-)millimeter wavelength should be observe. On the contrary, a compact millimeter emission it observed for about 50% of TDs by ALMA, as it is the case for the TD surrounding CQ Tau, a nearby, intermediate mass pre-main sequence star of spectral type F2. 

As of today, it is not clear if such compact emission is due to the presence of pebbles or whether it is due to non-thermal emission related, e.g., an ionized wind. To quantify this possibility, we performed a detailed multi-wavelength analysis to study the emission in the inner disk of CQ Tau, combining a large set of sensitive and high angular resolution continuum observations from ALMA and VLA, from 0.87 mm to 6 cm (see Figure 1, left panel). Our goal is to try and separate dust and gas emission in the inner region of this system. We present the results of a detailed spectral index analysis (see Figure 1, right panel) in order to characterize the nature of the emission in every part of the disk, extrapolate the free-free emission present and then finally separate between this emission and dust thermal emission for CQ Tau. Finally, we present initial attempts to extend these results to a broader sample of TDs, for which we collected the necessary observations.

Figure 1: CQ Tau. Left: Archival data at 1.3 mm (Band 6) of ALMA with in contours the archival data from VLA, at 2 cm (Ku Band). The contours levels are comprise between 10⁻⁵(white contour) and 2 × 10⁻⁵Jy.beam⁻¹ (red contour). A 1 arcsecond scale is shown in the upper part of the plot and the beam is presented on the left bottom corner. Right: Spectral index map using data at centimeter and millimeter wavelength. This computation is done pixels-by-pixels, all data smoothed to the lowest resolution map and each pixel’s color is set to the value of the spectral index. Values within the disk are comprise between 0 and 2.

How to cite: Armante, M., Fedele, D., Testi, L., and Natta, A.: Dust evolution in protoplanetary disks with SKA and precursors, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1872, https://doi.org/10.5194/epsc-dps2025-1872, 2025.