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Observations of protoplanetary disks provide information on planet formation and the reasons for the diversity of planetary systems. The key to understanding planet formation is the study of dust evolution from small grains to pebbles. Smaller grains are well-coupled to the gas dynamics, and their distribution is significantly extended above the disk midplane. Larger grains settle much faster and are efficiently formed only in the midplane. By combining near-infrared polarized light and millimeter observations, it is possible to constrain the spatial distribution of both the small and large grains. We aim to construct detailed models of the size distribution and vertical/radial structure of the dust particles in protoplanetary disks based on observational data. In particular, we are interested in recovering the dust distribution in the IM Lup protoplanetary disk. We create a physical model for the dust distribution of protoplanetary disks and simulate the radiative transfer of the millimeter continuum and the near-infrared polarized radiation. Using a Markov chain Monte Carlo method, we compare the derived images to the observations available for the IM Lup disk to constrain the best physical model for IM Lup and to recover the vertical grain size distribution. The millimeter and near-infrared emission tightly constrain the dust mass and grain size distribution of our model. We find size segregation in the dust distribution, with millimeter-sized grains in the disk midplane. These grains are efficiently formed in the disk, possibly by sedimentation-driven coagulation, in accord with the short settling timescales predicted by our model. This also suggests a high dust-to-gas ratio at smaller radii in the midplane, possibly triggering streaming instabilities and planetesimal formation in the inner disk., Comment: 15 pages, 16 figures, accepted by Astronomy & Astrophysics

The nucleosynthetic isotope dichotomy between carbonaceous (CC) and non-carbonaceous (NC) meteorites has been interpreted as evidence for spatial separation and the coexistence of two distinct planet-forming reservoirs for several million years in the solar protoplanetary disk. The rapid formation of Jupiter's core within one million years after the formation of calcium-aluminium-rich inclusions (CAIs) has been suggested as a potential mechanism for spatial and temporal separation. In this scenario, Jupiter's core would open a gap in the disk and trap inward-drifting dust grains in the pressure bump at the outer edge of the gap, separating the inner and outer disk materials from each other. We performed simulations of dust particles in a protoplanetary disk with a gap opened by an early-formed Jupiter core, including dust growth and fragmentation as well as dust transport, using the dust evolution software DustPy. Our numerical experiments indicate that particles trapped in the outer edge of the gap rapidly fragment and are transported through the gap, contaminating the inner disk with outer disk material on a timescale that is inconsistent with the meteoritic record. This suggests that other processes must have initiated or at least contributed to the isotopic separation between the inner and outer Solar System., Comment: Accepted for publication in Astronomy & Astrophysics Letters

Context. When we wish to understand planetesimal formation, the only data set we have is our own Solar System. The Solar System is particularly interesting because so far, it is the only planetary system we know of that developed life. Understanding the conditions under which the solar nebula evolved is crucial in order to understand the different processes in the disk and the subsequent dynamical interaction between (proto-)planets after the gas disk has dissolved. Aims. Protoplanetary disks provide a plethora of different parameters to explore. The question is whether this parameter space can be constrained, allowing simulations to reproduce the Solar System. Methods. Models and observations of planet formation provide constraints on the initial planetesimal mass in certain regions of the solar nebula. By making use of pebble flux-regulated planetesimal formation, we performed a parameter study with nine different disk parameters such as the initial disk mass, the initial disk size, the initial dust-to-gas ratio, the turbulence level, and others. Results. We find that the distribution of mass in planetesimals in the disk depends on the timescales of planetesimal formation and pebble drift. Multiple disk parameters can affect the pebble properties and thus planetesimal formation. However, it is still possible to draw some conclusions on potential parameter ranges. Conclusions. Pebble flux-regulated planetesimal formation appears to be very robust, allowing simulations with a wide range of parameters to meet the initial planetesimal constraints for the solar nebula. This means that it does not require much fine-tuning.

We combined hydrodynamical simulations of planet-disk interactions with dust evolution models that include coagulation and fragmentation of dust grains over a large range of radii and derived observational properties using radiative transfer calculations. We studied the role of the snow line in the survival of the inner disk of transition disks. Inside the snow line, the lack of ice mantles in dust particles decreases the sticking efficiency between grains. As a consequence, particles fragment at lower collision velocities than in regions beyond the snow line. This effect allows small particles to be maintained for up to a few Myrs within the first astronomical unit. These particles are closely coupled to the gas and do not drift significantly with respect to the gas. For lower mass planets (1$M_{\rm{Jup}}$), the pre-transition appearance can be maintained even longer because dust still trickles through the gap created by the planet, moves invisibly and quickly in the form of relatively large grains through the gap, and becomes visible again as it fragments and gets slowed down inside of the snow line. The global study of dust evolution of a disk with an embedded planet, including the changes of the dust aerodynamics near the snow line, can explain the concentration of millimetre-sized particles in the outer disk and the survival of the dust in the inner disk if a large dust trap is present in the outer disk. This behaviour solves the conundrum of the combination of both near-infrared excess and ring-like millimetre emission observed in several transition disks., Accepted for publication in A&A (including acknowledgments)

In order to explain grain growth to mm sized particles and their retention in outer regions of protoplanetary disks, as it is observed at sub-mm and mm wavelengths, we investigate if strong inhomogeneities in the gas density profiles can slow down excessive radial drift and can help dust particles to grow. We use coagulation/fragmentation and disk-structure models, to simulate the evolution of dust in a bumpy surface density profile which we mimic with a sinusoidal disturbance. For different values of the amplitude and length scale of the bumps, we investigate the ability of this model to produce and retain large particles on million years time scales. In addition, we introduced a comparison between the pressure inhomogeneities considered in this work and the pressure profiles that come from magnetorotational instability. Using the Common Astronomy Software Applications ALMA simulator, we study if there are observational signatures of these pressure inhomogeneities that can be seen with ALMA. We present the favorable conditions to trap dust particles and the corresponding calculations predicting the spectral slope in the mm-wavelength range, to compare with current observations. Finally we present simulated images using different antenna configurations of ALMA at different frequencies, to show that the ring structures will be detectable at the distances of the Taurus Auriga or Ophiucus star forming regions., Pages 15, Figures 14. Accepted for publication in Astronomy and Astrophysics

Context. The disk around the Herbig Ae star, HD 100546, shows structures that suggest the presence of two companions in the disk at $\sim10$ and $\sim70$ AU. The outer companion seems to be in the act of formation. Aims. Our aims are to provide constraints on the age of the planets in HD 100546 and to explore the potential evidence for sequential planet formation in transition disks such as HD 100546. Methods. We compare the recent resolved continuum observations of the disk around HD 100546 with the results of dust evolution simulations using an analytical prescription for the shapes of gaps carved by massive planets. Results. An inner pressure bump must have been present since early in the disk lifetime to have good agreement between the dust evolution models and the continuum observations of HD 100546. This pressure bump may have resulted from the presence of a very massive planet ($\sim20 M_{\rm{Jup}}$), which formed early in the inner disk ($r\sim$10 AU). If only this single planet exists, the disk is likely to be old, comparable to the stellar age ($\sim$5-10 Myr). Another possible explanation is an additional massive planet in the outer disk ($r\sim70$ AU): either a low-mass outer planet ($\lesssim5 M_{\rm{Jup}}$) injected at early times, or a higher mass outer planet ($\gtrsim15 M_{\rm{Jup}}$) formed very recently, traps the right amount of dust in pressure bumps to reproduce the observations. In the latter case, the disk could be much younger ($\sim3.0$ Myr). Conclusions. In the case in which two massive companions are embedded in the disk around HD 100546, as suggested in the literature, the outer companion could be at least $\gtrsim$2.5 Myr younger than the inner companion., Comment: Accepted for publication in A&A

Context. Grains in circumstellar disks are believed to grow by mutual collisions and subsequent sticking due to surface forces. Results of many fields of research involving circumstellar disks, such as radiative transfer calculations, disk chemistry, magneto-hydrodynamic simulations largely depend on the unknown grain size distribution. Aims. As detailed calculations of grain growth and fragmentation are both numerically challenging and computationally expensive, we aim to find simple recipes and analytical solutions for the grain size distribution in circumstellar disks for a scenario in which grain growth is limited by fragmentation and radial drift can be neglected. Methods. We generalize previous analytical work on self-similar steady-state grain distributions. Numerical simulations are carried out to identify under which conditions the grain size distributions can be understood in terms of a combination of power-law distributions. A physically motivated fitting formula for grain size distributions is derived using our analytical predictions and numerical simulations. Results. We find good agreement between analytical results and numerical solutions of the Smoluchowski equation for simple shapes of the kernel function. The results for more complicated and realistic cases can be fitted with a physically motivated "black box" recipe presented in this paper. Our results show that the shape of the dust distribution is mostly dominated by the gas surface density (not the dust-to-gas ratio), the turbulence strength and the temperature and does not obey an MRN type distribution., Comment: 16 pages, 9 figures, accepted for publication in A&A

Context. Current models of the size- and radial evolution of dust in protoplanetary disks generally oversimplify either the radial evolution of the disk (by focussing at one single radius or by using steady state disk models) or they assume particle growth to proceed monodispersely or without fragmentation. Further studies of protoplanetary disks - such as observations, disk chemistry and structure calculations or planet population synthesis models - depend on the distribution of dust as a function of grain size and radial position in the disk. Aims. We attempt to improve upon current models to be able to investigate how the initial conditions, the build-up phase, and the evolution of the protoplanetary disk influence growth and transport of dust. Methods. We introduce a new version of the model of Brauer et al. (2008) in which we now include the time-dependent viscous evolution of the gas disk, and in which more advanced input physics and numerical integration methods are implemented. Results. We show that grain properties, the gas pressure gradient, and the amount of turbulence are much more influencing the evolution of dust than the initial conditions or the build-up phase of the protoplanetary disk. We quantify which conditions or environments are favorable for growth beyond the meter size barrier. High gas surface densities or zonal flows may help to overcome the problem of radial drift, however already a small amount of turbulence poses a much stronger obstacle for grain growth., Comment: accepted to A&A