Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Dust settling and rings in the outer regions of protoplanetary discs
  subject to ambipolar diffusion   MHD turbulence plays a crucial role in the dust dynamics of protoplanetary
discs. It affects planet formation, vertical settling and is one possible
origin of the large scale axisymmetric structures, such as rings, recently
imaged by ALMA and SPHERE. Among the variety of MHD processes, the
magnetorotational instability (MRI) has raised particular interest since it
provides a source of turbulence and potentially organizes the flow into radial
structures. However, the weak ionization of discs prevents the MRI from being
excited beyond 1 AU. The strong sedimentation of millimetre dust measured in
T-Tauri discs is also in contradiction with predictions based on ideal MRI
turbulence. In this paper, we study the effects of non-ideal MHD and winds on
the dynamics and sedimentation of dust grains. We consider a weakly ionized
plasma subject to ambipolar diffusion characterizing the disc outer regions (>1
AU). For that, we perform numerical MHD simulations in the stratified shearing
box, using the PLUTO code. Our simulations show that the mm-cm dust is
contained vertically in a very thin layer, with typical heightscale ~0.4 AU at
30 AU, compatible with recent ALMA observations. Horizontally, the grains are
trapped within pressure maxima induced by ambipolar diffusion, leading to the
formation of dust rings. For micrometer grains, dust and gas scaleheights are
similar. In this regime, the settling cannot be explained by a simple 1D
diffusion theory but results from a large scale 2D circulation induced by both
MHD winds and zonal flows. Overall, our results show that non-ideal MHD effects
and their related winds play a major role in shaping the radial and vertical
distribution of dust in protoplanetary discs. Leading to substantial accretion
efficiency, non-ideal effects also a promising avenue to reconcile the low
turbulent activity measured in discs with their relatively high accretion
rates.

31
The categories of this paper are: ao-sci
16
The categories of this paper are: stat
19
The categories of this paper are: eess
14
The categories of this paper are: math-ph
37
The categories of this paper are: supr-con
20
The categories of this paper are: acc-phys
27
The categories of this paper are: comp-gas
5
The categories of this paper are: gr-qc
29
The categories of this paper are: funct-an
22
The categories of this paper are: chao-dyn
1
The categories of this paper are: cs
17
The categories of this paper are: q-fin
3
The categories of this paper are: physics
8
The categories of this paper are: hep-ex
28
The categories of this paper are: alg-geom
10
The categories of this paper are: q-bio