Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The magnetorotational instability in debris-disc gas   Debris discs are commonly swathed in gas which can be observed in UV, in fine
structure lines in FIR, and in resolved maps of CO emission. Carbon and oxygen
are overabundant in such gas, but it is severely depleted in hydrogen. As a
consequence, its ionisation fraction is remarkably high, suggesting
magnetohydrodynamic (MHD) processes may be important. In particular, the gas
may be subject to the magnetorotational instability (MRI), and indeed recent
modelling of $\beta$ Pictoris requires an anomalous viscosity to explain the
gas's observed radial structure. In this paper we explore the possibility that
the MRI is active in debris-disc gas and responsible for the observed mass
transport. We find that non-ideal MHD and dust-gas interactions play a
subdominant role, and that linear instability is viable at certain radii.
However, owing to low gas densities, the outer parts of the disc could be
stabilised by a weak ambient magnetic field, though it is difficult to
constrain such a field. Even if the MRI is stabilised by too strong a field, a
magnetocentrifugal wind may be launched in its place and this could lead to
equivalent (non-turbulent) transport. Numerical simulations of the vertically
stratified MRI in conditions appropriate to the debris disc gas should be able
to determine the nature of the characteristic behaviour at different radii, and
decide on the importance of the MRI (and MHD more generally) on the evolution
of these discs.

36
The categories of this paper are: cmp-lg
10
The categories of this paper are: q-bio
28
The categories of this paper are: alg-geom
2
The categories of this paper are: math
34
The categories of this paper are: chem-ph
35
The categories of this paper are: mtrl-th
14
The categories of this paper are: math-ph
23
The categories of this paper are: solv-int
4
The categories of this paper are: cond-mat
0
The categories of this paper are: hep-ph
25
The categories of this paper are: patt-sol
26
The categories of this paper are: bayes-an
12
The categories of this paper are: nucl-th
33
The categories of this paper are: plasm-ph
19
The categories of this paper are: eess
1
The categories of this paper are: cs