We analyzed the mechanism of low-temperature crystallization of an amorphous silicate grain due t... more We analyzed the mechanism of low-temperature crystallization of an amorphous silicate grain due to exothermic chemical reactions in the surface layer of the grains as demonstrated experimentally (Kaito et al. 2007, ApJ. 666, L57). We constructed a model of the crystallization and derived the crystallization conditions of the amorphous silicate core of the grain. The analysis enables us to obtain the crystallization conditions in protoplanetary disks. Our results suggest that silicate crystallization occurs in a wider variety of conditions than hitherto considered.
Dust particles in orbit around a star drift toward the central star by the Poynting-Robertson eff... more Dust particles in orbit around a star drift toward the central star by the Poynting-Robertson effect and pile up by sublimation. We analytically derive the pile-up magnitude, adopting a simple model for optical cross sections. As a result, we find that the sublimation temperature of drifting dust particles plays the most important role in the pile-up rather than their optical property does. Dust particles with high sublimation temperature form a significant dust ring, which could be found in the vicinity of the sun through in-situ spacecraft measurements. While the existence of such a ring in a debris disk could not be identified in the spectral energy distribution (SED), the size of a dust-free zone shapes the SED. Since we analytically obtain the location and temperature of sublimation, these analytical formulae are useful to find such sublimation evidences.
The impact of solar wind particles exerts a drag force on interplanetary dust grains in the same ... more The impact of solar wind particles exerts a drag force on interplanetary dust grains in the same manner as electro-magnetic drag so called the Poynting-Robertson effect. We study this plasma drag for fluffy aggregates particles with assumptions for the shape structure, and composition of the aggregates plausible for dust in the solar system. First, we calculate the plasma drag for single spherical grains taking into account the penetration of incident solar wind ions as a basis of evaluating the drag for fluffy aggregates consisting of spherical monomers. We find that the size dependence of the plasma drag is analogous to the electro-magnetic drag. Namely, 1) for the monomers smaller than the penetration depth of the solar wind ions, the plasma drag is proportional to the volume of the grain, whereas 2) for the monomers larger than the penetration depth, the drag is proportional to the geometrical cross section of a monomer. Although the penetration of solar wind ions through a mono...
In protoplanetary disks, dust aggregates consisting of submicron particles grow through their mut... more In protoplanetary disks, dust aggregates consisting of submicron particles grow through their mutual collisions. In the early growth stage, dust aggregates collide with each other at extremely low velocities (< 1 mm/s) due to strong coupling with disk gas. Because of such low-velocity collisions, the growing dust aggregates are thought to have a structure similar to the ballistic cluster-cluster aggregation (BCCA) clusters, which are formed by a series of hit-and-sticks of comparable aggregates and have a fluffy structure with fractal dimension 2. Such BCCA-like aggregates would be compressed with increasing collision energy and may end up with disruption at high-velocity collisions. We perform direct N-body simulations of aggregate collisions with the use of realistic binding forces in order to investigate the collisional growth and disruption processes of dust aggregates. As a result, we find that aggregates formed through collisions between BCCA clusters have a fractal dimensi...
We carry out numerical simulations of collisions of aggregates with various coordination numbers ... more We carry out numerical simulations of collisions of aggregates with various coordination numbers to investigate the bouncing conditions and collosional growth possibility of dust in protoplanetary disks.
We analyzed the mechanism of low-temperature crystallization of an amorphous silicate grain due t... more We analyzed the mechanism of low-temperature crystallization of an amorphous silicate grain due to exothermic chemical reactions in the surface layer of the grains as demonstrated experimentally (Kaito et al. 2007, ApJ. 666, L57). We constructed a model of the crystallization and derived the crystallization conditions of the amorphous silicate core of the grain. The analysis enables us to obtain the crystallization conditions in protoplanetary disks. Our results suggest that silicate crystallization occurs in a wider variety of conditions than hitherto considered.
Dust particles in orbit around a star drift toward the central star by the Poynting-Robertson eff... more Dust particles in orbit around a star drift toward the central star by the Poynting-Robertson effect and pile up by sublimation. We analytically derive the pile-up magnitude, adopting a simple model for optical cross sections. As a result, we find that the sublimation temperature of drifting dust particles plays the most important role in the pile-up rather than their optical property does. Dust particles with high sublimation temperature form a significant dust ring, which could be found in the vicinity of the sun through in-situ spacecraft measurements. While the existence of such a ring in a debris disk could not be identified in the spectral energy distribution (SED), the size of a dust-free zone shapes the SED. Since we analytically obtain the location and temperature of sublimation, these analytical formulae are useful to find such sublimation evidences.
The impact of solar wind particles exerts a drag force on interplanetary dust grains in the same ... more The impact of solar wind particles exerts a drag force on interplanetary dust grains in the same manner as electro-magnetic drag so called the Poynting-Robertson effect. We study this plasma drag for fluffy aggregates particles with assumptions for the shape structure, and composition of the aggregates plausible for dust in the solar system. First, we calculate the plasma drag for single spherical grains taking into account the penetration of incident solar wind ions as a basis of evaluating the drag for fluffy aggregates consisting of spherical monomers. We find that the size dependence of the plasma drag is analogous to the electro-magnetic drag. Namely, 1) for the monomers smaller than the penetration depth of the solar wind ions, the plasma drag is proportional to the volume of the grain, whereas 2) for the monomers larger than the penetration depth, the drag is proportional to the geometrical cross section of a monomer. Although the penetration of solar wind ions through a mono...
In protoplanetary disks, dust aggregates consisting of submicron particles grow through their mut... more In protoplanetary disks, dust aggregates consisting of submicron particles grow through their mutual collisions. In the early growth stage, dust aggregates collide with each other at extremely low velocities (< 1 mm/s) due to strong coupling with disk gas. Because of such low-velocity collisions, the growing dust aggregates are thought to have a structure similar to the ballistic cluster-cluster aggregation (BCCA) clusters, which are formed by a series of hit-and-sticks of comparable aggregates and have a fluffy structure with fractal dimension 2. Such BCCA-like aggregates would be compressed with increasing collision energy and may end up with disruption at high-velocity collisions. We perform direct N-body simulations of aggregate collisions with the use of realistic binding forces in order to investigate the collisional growth and disruption processes of dust aggregates. As a result, we find that aggregates formed through collisions between BCCA clusters have a fractal dimensi...
We carry out numerical simulations of collisions of aggregates with various coordination numbers ... more We carry out numerical simulations of collisions of aggregates with various coordination numbers to investigate the bouncing conditions and collosional growth possibility of dust in protoplanetary disks.
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