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Y. Nakagawa, H. Nomura (Kobe University)
Particle settling and growth are important processes leading to planetary accumulation in the protoplanetary disks. There may exist turbulent motion raised by magneto-rotational or convective instabilities in the disks; such tubulence will affect particle settling and growth, and vice versa. In the present study we examined particle settling and growth in two cases of quiescent and turbulent disks by numerically solving the coagulation equation for settling particles with very fine resolution.
We found in quescent disks the dust particles settle into a very thin layer where the gravitational instability can occur; the settling time is 2\times 103 -- 5\times 104 years in the zones of the radial distances 1 -- 30AU and the largest particle size is 20 -- 0.6cm in those zones. These results are quite simolar to the analytic estimates by Nakagawa et al. (1986) who did not take into account the particle size distribution explicitly.
Numerical results in the zone of 30AU in turbulent disks show that the dust particles first grow to several cm sizes with no appreciable settling, then become free from turbulent eddies, and settle into a layer as thin as 10-4AU; however, they oscillate aroun the central plane with the amplitude of (vt/cs)H, where vt is the turbulent velocity, cs in the sound velocity, and H is the halh thickness of the disk. We will futher discuss the particle settling and growth, taking into account the time evolution of turbulence raised by instabilities above.
The study is supported by the 21st Centry COE Program: Origin and Evolution of Planetary Systems of the Ministry of Education, Culture, Sports, Science, and Technology, Japan, anf Grant-in-Aid for Scientific Research (C) 17540217 of the Japan Society for the Promotion of Science.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.