Thinkshop 2020

Magnetically driven disk winds (MDWs) are one of the promising mechanisms of dispersal processes of protoplanetary disks (Suzuki et al. 2010, Bai 2013). When the MDWs play a key role, the gaseous component of protoplanetary disks evolves in a different manner from that of the classical viscous evolution. As a result, the subsequent planet formation is also affected by the MDWs. In this work, we investigate the effects of the MDWs on the radial drift of solid particles with a size of 0.1$\mu$m - 1km. We propose that the MDWs is a possible solution to the ``radial drift barrier'' of collisionally growing dust grains, which is a severe obstacle to the planet formation (e.g., Nakagawa et al.1986).
In order to study the evolution of dust grains in the disks, we calculate the advection and collisional growth of dust particles in evolving protoplanetary disks under the 1+1 D (time + radial distance) approximation. We solve a coagulation equation of solid particles under a single-size approximation (Sato et al. 2016) for various conditions of turbulent viscosity, the mass loss by the MDW, and the magnetic braking by the MDW.
We found that significant grain growth occurs in the inner region of the protoplanetary disks. The grown dust particles are larger than the km-sized bodies and they are no longer caught by the radial drift barrier. The mechanism of such successful dust growth is separated into two parts: (1) the increase of the equilibrium size of the dust particles caused by the convergent flow of the dust mass and dispersal of the gas component, (2) the unstable dust growth driven by the feedback loop between the size, radial drift velocity, and surface density of the dust component. The disk evolution owing to the MDWs strongly supports the former part of the growth mechanism. When the equilibrium size of the dust particles reaches the size that the Stokes number of the dust particles exceeds unity, the dust size evolution shift to the unstable mode (i.e., the latter part).
Because of the successful growth of dust particles, the ring-like structure containing the planetesimal sized bodies can be formed at the inner part of the protoplanetary disks. We will discuss the effects of such the ring-like structure on the subsequent planetary system formation and the disk observations.