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Context. Crystalline silicates are an important tracer of the evolution of dust, the main building block of planet formation. In an inner protoplanetary disk, amorphous silicates are annealed because of the high temperatures that prevail there. These crystalline silicates are radially and vertically distributed by a disk turbulence and/or radial transport. Mid-infrared spectrographs are sensitive to the presence and temperature of micron-sized silicates, and the dust temperature can be used to infer their spatial distribution. Aims. We aim to model the spatial distribution of crystalline silicate dust in protoplanetary disks taking into account thermal annealing of silicate dust and radial transport of dust in the midplane. Using the resulting spatial distribution of crystalline and amorphous silicates, we calculated mid-infrared spectra to study the effect on dust features and to compare these to observations. Methods. We modeled a Class II T-Tauri protoplanetary disk and defined the region where crystallization happens by thermal annealing process from the comparison between crystallization and residence timescales ($ cryst res $). Radial mixing and drift were also compared to find a vertically well mixed region ($ ver drift $). We used the DISKLAB code to model the radial transport in the midplane and obtained the spatial distribution of the crystalline silicates for different grain sizes. We used MCMax, a radiative transfer code, to model the mid-infrared spectrum. Results. In our modeled T-Tauri disk, different grain sizes get crystallized in different radial and vertical ranges within 0.2 au. Small dust gets vertically mixed up efficiently, so crystallized small dust in the disk surface is well mixed with the midplane. Inward of 0.075 au, all grains are fully crystalline irrespective of their size. We also find that the crystallized dust is distributed out to a few au by radial transport, smaller grains more so than larger ones. Our fiducial model shows different contributions of the inner and outer disks to the dust spectral features. The $10 forsterite feature has an $ 30 <!PCT!>$ contribution from the innermost disk (0.07-0.09 au) and $<1 <!PCT!>$ from the disk beyond 10 au while the $33 feature has an $ 10 <!PCT!>$ contribution from both innermost and outer disks. We also find that feature strengths change when varying the spatial distribution of crystalline dust. Our modeled spectra qualitatively agree with observations from the Spitzer Space Telescope, but the modeled 10 mu m feature is strongly dominated by crystalline dust, unlike observations. Models with reduced crystallinity and depletion of small crystalline dust within 0.2 au show a better match with observations. Conclusions. Mid-infrared observations of the disk surface represent the radial distribution of small dust grains in the midplane and provide us with abundances of crystalline and amorphous dust, size distribution, and chemical composition in the inner disk. The inner and outer disks contribute more to shorter and longer wavelength features, respectively. In addition to the crystallization and dynamical processes, amorphization, sublimation of silicates, and dust evolution have to be taken into account to match observations, especially at $ where the inner disk mostly contributes. This study could interpret spectra of protoplanetary disks taken with the Mid-Infrared Instrument (MIRI) on board the James Webb Space Telescope.
Context. Crystalline silicates are an important tracer of the evolution of dust, the main building block of planet formation. In an inner protoplanetary disk, amorphous silicates are annealed because of the high temperatures that prevail there. These crystalline silicates are radially and vertically distributed by a disk turbulence and/or radial transport. Mid-infrared spectrographs are sensitive to the presence and temperature of micron-sized silicates, and the dust temperature can be used to infer their spatial distribution. Aims. We aim to model the spatial distribution of crystalline silicate dust in protoplanetary disks taking into account thermal annealing of silicate dust and radial transport of dust in the midplane. Using the resulting spatial distribution of crystalline and amorphous silicates, we calculated mid-infrared spectra to study the effect on dust features and to compare these to observations. Methods. We modeled a Class II T-Tauri protoplanetary disk and defined the region where crystallization happens by thermal annealing process from the comparison between crystallization and residence timescales ($ cryst res $). Radial mixing and drift were also compared to find a vertically well mixed region ($ ver drift $). We used the DISKLAB code to model the radial transport in the midplane and obtained the spatial distribution of the crystalline silicates for different grain sizes. We used MCMax, a radiative transfer code, to model the mid-infrared spectrum. Results. In our modeled T-Tauri disk, different grain sizes get crystallized in different radial and vertical ranges within 0.2 au. Small dust gets vertically mixed up efficiently, so crystallized small dust in the disk surface is well mixed with the midplane. Inward of 0.075 au, all grains are fully crystalline irrespective of their size. We also find that the crystallized dust is distributed out to a few au by radial transport, smaller grains more so than larger ones. Our fiducial model shows different contributions of the inner and outer disks to the dust spectral features. The $10 forsterite feature has an $ 30 <!PCT!>$ contribution from the innermost disk (0.07-0.09 au) and $<1 <!PCT!>$ from the disk beyond 10 au while the $33 feature has an $ 10 <!PCT!>$ contribution from both innermost and outer disks. We also find that feature strengths change when varying the spatial distribution of crystalline dust. Our modeled spectra qualitatively agree with observations from the Spitzer Space Telescope, but the modeled 10 mu m feature is strongly dominated by crystalline dust, unlike observations. Models with reduced crystallinity and depletion of small crystalline dust within 0.2 au show a better match with observations. Conclusions. Mid-infrared observations of the disk surface represent the radial distribution of small dust grains in the midplane and provide us with abundances of crystalline and amorphous dust, size distribution, and chemical composition in the inner disk. The inner and outer disks contribute more to shorter and longer wavelength features, respectively. In addition to the crystallization and dynamical processes, amorphization, sublimation of silicates, and dust evolution have to be taken into account to match observations, especially at $ where the inner disk mostly contributes. This study could interpret spectra of protoplanetary disks taken with the Mid-Infrared Instrument (MIRI) on board the James Webb Space Telescope.
Previous high-angular-resolution 225 GHz (sim 1.3 mm) continuum observations of the transitional disk DM Tau have resolved an outer ring at 20-120 au radii that is weakly azimuthally asymmetric. We aim to examine dust growth and filtration in the outer ring of DM Tau. We performed sim 0 (sim 8.7 au) resolution Karl G. Jansky Very Large Array (JVLA) 40--48 GHz ($ 7$ mm; Q band) continuum observations, along with complementary observations at lower frequencies. In addition, we analyzed the archival JVLA observations undertaken since 2010. Intriguingly, the Q band image resolved the azimuthally highly asymmetric, knotty dust emission sources close to the inner edge of the outer ring. Fitting the 8-700 GHz spectral energy distribution (SED) with two dust components indicates that the maximum grain size ($a_ max $) in these knotty dust emission sources is likely gtrsim 300 mu m, whereas it is lesssim 50 mu m in the rest of the ring. These results may be explained by a trapping of inwardly migrating "grown" dust close to the ring inner edge. The exact mechanism for developing the azimuthal asymmetry has not yet been identified, which may be due to planet-disk interaction that might also be responsible for the creation of the dust cavity and pressure bump. Otherwise, it may be due to the fluid instabilities and vortex formation as a result of shear motions. Finally, we remark that the asymmetries in DM Tau are difficult to diagnose from the gtrsim 225 GHz observations, owing to a high optical depth at the ring. In other words, the apparent symmetric or asymmetric morphology of the transitional disks may be related to the optical depths of those disks at the observing frequency.
In protoplanetary discs, micron-sized dust grows to form millimetre- to centimetre-sized pebbles but encounters several barriers during its evolution. Collisional fragmentation and radial drift impede further dust growth to planetesimal size. Fluffy grains have been hypothesised to solve these problems. While porosity leads to faster grain growth, the implied porosity values obtained from previous simulations were larger than suggested by observations. In this paper, we study the influence of porosity on dust evolution, taking into account growth, bouncing, fragmentation, compaction, rotational disruption, and snow lines, in order to understand their impact on dust evolution. We developed a module for porosity evolution for the 3D smoothed particle hydrodynamics code Phantom that accounts for dust growth and fragmentation. This mono-disperse model is integrated into both a 1D code and the 3D code to capture the overall evolution of dust and gas. We show that porosity helps dust growth and leads to the formation of larger solids than when considering compact grains, as predicted by previous work. Our simulations taking into account compaction during fragmentation show that large millimetre grains are still formed but are ten to 100 times more compact. Thus, millimetre sizes with typical filling factors of $ match the values measured on comets or via polarimetric observations of protoplanetary discs.
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