Building Blocks of Planets 2020 Abstract Booklet - Tuesday 14.4.2020 - Scattering-induced intensity reduction: large mass content with small grains in the inner region of the TW Hya disk Takahiro Ueda Dust continuum observation is one of the best methods to constrain the properties of protoplanetary disks. Recent theoretical studies have suggested that the dust scattering at the millimeter wavelength potentially reduces the observed intensity, which results in an underestimate in the dust mass. We investigate whether the dust scattering indeed reduces the observed continuum intensity by comparing the ALMA archival data of the TW Hya disk at Band 3, 4, 6, 7 and 9 to models obtained by radiative transfer simulations. We find that the model with scattering reproduces the observed SED of the central part of the TW Hya disk best while the model without scattering is still consistent within the conservative errors of the absolute fluxes. To explain the intensity at Band 3, the dust surface density needs to be ∼ 10 g cm^−2 at 10 au in the model with scattering, which is 26 times more massive than previously predicted. The model without scattering needs 2.3 times higher dust mass than the model with scattering because the model without scattering needs lower temperature. At Band 7, even though the disk is optically thick, scattering reduces the intensity by ∼ 35% which makes the disk looks optically thin. Our study suggests the TW Hya disk is still capable of forming cores of giant planets at where the current solar system planets exist. Tracing dust evolution from cores to disks Leonardo Testi I will discuss observational evidence for dust evolution from cores too disks. I will focus on the uncertainties and pitfalls, what we think we have learned and what we perhaps need to revisit with a new perspective. I will mostly, but not only, focus on how ALMA observations have changed our perspective and highlight some of the future directions that are required to progress in the observational characterization of dust evolution. Dust evolution as disk mass estimate Riccardo Franceschi The dust content is fundamental for the structure and observation of protoplanetary disks. Moreover, observations of dust emission have been used in most of disk mass estimates, assuming a constant dust-to-mass ratio. However, dust properties should be changing in an evolving disk, depending on the structure of the disk and the grain size distribution, both uncertain quantities. Dust particles are subjected to radial drift, gas drag and turbulent mixing, and all these processes depends on grain size. This causes a grain size differentiation along the disk structure that, along consideration on grain growth, can be used to derive the total disk surface density profile. This approach can be checked with multiwavelength observation of dust line location for different sized grain in several disks, and could provide constraint to disk mass estimates. Edge-on observations of young disks Marion Villenave To form giant planets in protoplanetary disk lifetime, small micron sized particles must grow rapidly to larger grains. To do so, they need to settle efficiently towards the disk midplane, and likely concentrate into dust traps. Currently observational constraints on vertical settling, which is intrinsically related to grain growth, are incomplete. During this talk, I aim to present new observational constraints on vertical settling efficiency. I will compare optical/infrared scattered light with millimeter observations of several edge-on disks, to probe the difference in vertical extent between micron-sized and larger millimeter-sized dust grains. I will show that the most edge-on disks of our sample, well resolved vertically, are compatible with having a millimeter dust scale height of about 1au at 100 au. Compared to a gas scale height estimated to about 10 au at 100 au, this result indicates very efficient vertical settling. This increasing dust density in the midplane is expected to enhance the efficiency of planet formation. Dust models after Planck Vincent Guillet Dust models are key to study the nature of interstellar grains and the processes that govern the evolution of their properties through the interstellar medium. In this talk, I will focus on the importance of dust models for the analysis of polarization observations. I will show how far-infrared and submillimeter observations by Planck and BLASTPol have ruled out historical dust models, and forced to a revision that is still ongoing. In the context of protoplanetary disks, I will advocate for the use of physical dust models to confidently interpret polarization patterns by aligned grains when the wavelength is of the order of the grain size. Polarization as a tool for characterizing cosmic dust particles Characterizing Cosmic dust Olga Muñoz The IAA Cosmic Dust Laboratory (Muñoz et al., JQSRT, 2010) has produced an important number of experimental phase functions and degree of linear polarization curves of cosmic dust analogues. The studied samples comprise a wide range of sizes (from sub-micron up to mm-sized), shapes and compositions. I will discuss our current efforts to constraint the parameter space (size, shape and refractive index) of cosmic dust grains by direct comparison of laboratory data with astronomical observations. Size and Structures in Disks around Very Low Mass Stars Nicolas Kurtovic Most of the stars in our galaxy are M-dwarfs, which are commonly hosts of planetary systems, which we know are formed in protoplanetary disks. Although planet formation models predict very efficient radial drift in the disks of these objects, millimeter wavelength observations have revealed the existence of circumstellar disks around them, suggesting the existence of strong pressure bumps. In this talk I will show our observations of 5 disks around VLMS in Taurus. With 0.1'' angular resolution we resolve the emission in all the disks, and we find evidence of substructure in 2 of them. By observing the molecular line emission 12CO and 13CO we find the gas radii being 3~6 times more extended than dust radii, larger than ratios observed in disks hosted by solar type stars or more massive. With these observations the total number of disks around VLMS in Taurus increases to 6, with clear evidence of substructure in at least 3 of them. Formation of multiple dust rings and gaps due to intermittent planet migration in protoplanetary disks Gaylor Wafflard-Fernandez Recent observations of spatially resolved protoplanetary disks, in particular with the radio interferometer ALMA, reveal a large diversity of substructures in the dust thermal emission (sequences of dark rings (gaps) and bright rings, asymmetries, spirals, ...). A key challenge for protoplanetary disks and planet formation models is to be able to make a reliable connection between these observed substructures and the supposed existence of planets impacting the dust content of protoplanetary disks. The observation of N dark rings of emission is often interpreted as evidence for the presence of N planets which clear dust gaps around their orbit and form dust- trapping pressure maxima in the disk. In general, these models assume planets on fixed orbits. We choose here to take into account the gravitational interaction between a planet and the gas content of a protoplanetary disk. We thus consider the large-scale inward migration of a single planet in a massive disk. In many circumstances, the migration of a partial gap-opening planet with a mass comparable to Saturn is found to run away intermittently. By means of 2D gas and dust hydrodynamical simulations, we show that intermittent runaway migration can form multiple dust rings and gaps across the disk. Each time migration slows down, a pressure maximum forms beyond the planet gap that traps the large dust. Post-processing of our simulations results with 3D dust radiative transfer calculations confirms that intermittent runaway migration can lead to the formation of multiple sets of bright and dark rings of continuum emission in the (sub)millimeter beyond the planet location. Signatures of planet formation and orbital evolution in the cold dust emission of protoplanetary discs Clément Baruteau The classical picture of protoplanetary discs being smooth, continuous structures of gas and dust has been challenged by the growing number of spatially resolved observations. These observations tell us that radial discontinuities and large-scale asymmetries are common features of the emission of protoplanetary discs, which are often interpreted as signatures of the presence of (unseen) planetary companions. During this seminar, I will report on our recent and ongoing work on how the formation and orbital evolution of planets impact the dust emission in protoplanetary discs, mainly at radio wavelengths. Through gas and dust hydrodynamical simulations post-processed with dust radiative transfer calculations, I will show that recent ALMA observations strongly suggest the presence of several planets in the discs around MWC 758 and HD 169142. Mdust-Mstar & Roust-Mstar relations: Models vs. Observations Paola Pinilla Demographic surveys of protoplanetary disks, in particular with ALMA, have provided access to a large range of disk dust masses and radii around stars with different stellar types and in different star-forming regions. These surveys found a power-law relation between Must (and Rdust) and Mstar that steepens in time, but which is also flatter for transition disks and disks with sub-structures. In this talk, I will present the results of dust evolution models that focus on investigating the effect of particle traps on these observed relations. I will explain what are the required conditions to reproduce the observed trends, in particular I will focus on what we can learn about the origins of the pressure traps in protoplanetary disks. Characterizing the dust content of protoplanetary disk substructures using multiwavelength (sub-)mm observations Enrique Macias A key piece of information to understand the origin and role of disk substructures is their dust content.