Streaming instabilities in accreting protoplanetary disks : A parameter study

Shiang-Chih Wang^1,2*, Min-Kai Lin^2,3

¹Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
²Institute of Astronomy and Astrophysics, Academia Sinica, Taipei, Taiwan
³Physics Division, National Center for Theoretical Sciences, Taipei, Taiwan

* Presenter:Shiang-Chih Wang, email:schihwang@gmail.com

The streaming instability (SI) is one of the key mechanism to form km-sized planetesimals from dust grains or pebbles, which is a critical step in the standard core accretion scenario of planet formation. By enhancing the local dust-to-gas ratio to the point of gravitational collapse, the SI can overcome the collisional and radial drift barriers to grain growth. Recent study finds that there is a new form of SI driven by the azimuthal velocity difference between dust and gas, which results from the gas undergoing accretion due to magnetic torques. This azimuthal-drift SI (AdSI) can remain effective even without a radial pressure gradient, unlike the classical SI. In our work, we extend previous simulations of the AdSI and classical SI by carrying out a large parameter survey using axisymmetric shearing box simulations. With the dust grain initially settle at midplane, AdSI produces vertically extended dust filaments for initial dust-to-gas ratios as low as ϵ = 0.01, and maximum dust-to-gas ratios of order 100 are attained for ϵ > 1, which can be expected to undergo gravitational collapse. We also find that accretion flow drives filament formation even in systems dominated by the classical SI. Furthermore, to see how filament structures change in a stratified disk, we include vertical gravity in our disk models. We present some initial investigations on stratified simulations of the AdSI in this presentation. Our study shed light on whether or not the AdSI can induce strong clumping or trigger the classical SI, which can then facilitate planetesimal formations.

Keywords: Planet formation, Protoplanetary disks, Astrophysical fluid dynamics