Dust settling and growth in protoplanetary disks and its implication for formation of extrasolar planets

行星系统是在原行星盘中形成的，原行星盘是恒星形成的副产品。这些圆盘由98- 99%的氢氦气体和残留的尘埃颗粒组成。尘埃凝结成星子，星子吸积成类地行星和类木行星的核心。在这项研究中，我们研究了从尘埃到星子的过程细节。尘埃颗粒之间的碰撞不一定会导致合并。通过数值模拟得出了破坏合并的条件（Wada et al. 2007）。n体模拟也研究了尘埃对团块（星子）的自引力不稳定性（Michikoshi et al. 2007）。另一方面，假设尘埃碰撞完全粘附，我们模拟了尘埃大小分布随圆盘半径和高度的变化，计算了圆盘的尘埃辐射，并将结果与观测数据进行了比较（Tanaka et al. 2005）。我们发现，尘埃辐射在数百万年的时间尺度上随着尘埃的增长而衰减，这意味着这种衰减并不一定意味着圆盘气体的耗尽。讨论了对射电观测的启示。根据理论模型，我们发现“AKARI”空间望远镜可以探测到低至月球质量的圆盘尘埃成分，并在此基础上确定了调查项目。我们还开发了IDL用于恒星/行星形成研究的管道。此外，我们发现ALMA的高精度图像可以检测到内外盘尘埃生长的差异。

Planetary systems are formed in protoplanetary disks that are by-products of star formation. The disks consist of 98-99 wt.% of H-He gas and residual dust grains. The dust coagulates into planetesimals and the planetesimals accrete into terrestria planets and cores of jovian planets.In this study, we investigated details of processes from dust to planetesimals. Collisions between dust grains do not necessarily result in coalescence. The conditions for coalescence of disruption were derived by numerical simulations (Wada et al. 2007). Self-gravitational instability of dust to clumps (planetesimals) was also studied by N-body simulations (Michikoshi et al. 2007). On the other hands, assuming complete sticking of dust collisions, we simulated evolution of dust size distributions as functions of radius and height of disks to calculate dust radiation from the disks and compare the results with observational data (Tanaka et al. 2005). We found that dust radiation decays on timescales of million years by growth of dust, wchich means that the decay does not necessarily imply depletion of disk gas.We also discussed implication for radio observation. With the theoretical model, we found that "AKARI" space telescope can detect dust components of disks down to Moon mass and fixed the survey project based on it. We also developed pipelines for star/planet formation study with IDL. Furthermore, we found that high-precision images by ALMA can detect difference in dust growth between inner and outer disks.