Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A Magnetically Torqued Disk Model for Be Stars   Despite extensive study, the mechanisms by which Be star disks acquire high
densities and angular momentum while displaying variability on many time scales
are still far from clear. In this paper, we discuss how magnetic torquing may
help explain disk formation with the observed quasi-Keplerian (as opposed to
expanding) velocity structure and their variability. We focus on the effects of
the rapid rotation of Be stars, considering the regime where centrifugal forces
provide the dominant radial support of the disk material. Using a kinematic
description of the angular velocity, vphi(r), in the disk and a parametric
model of an aligned field with a strength B(r) we develop analytic expressions
for the disk properties that allow us to estimate the stellar surface field
strength necessary to create such a disk for a range of stars on the
main-sequence. The model explains why disks are most common for main-sequence
stars at about spectral class B2 V. The earlier type stars with very fast and
high density winds would require unacceptably strong surface fields (> 10^3
Gauss) to form torqued disks, while the late B stars (with their low mass loss
rates) tend to form disks that produce only small fluxes in the dominant Be
diagnostics. For stars at B2 V the average surface field required is about 300
Gauss. The predicted disks provide an intrinsic polarization and a flux at
Halpha comparable to observations. We also discuss whether the effect on field
containment of the time dependent accumulation of matter in the flux tubes/disk
can help explain some of the observed variability of Be star disks.

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The categories of this paper are: comp-gas
5
The categories of this paper are: gr-qc
22
The categories of this paper are: chao-dyn
4
The categories of this paper are: cond-mat
32
The categories of this paper are: atom-ph
37
The categories of this paper are: supr-con
18
The categories of this paper are: econ
3
The categories of this paper are: physics
35
The categories of this paper are: mtrl-th
36
The categories of this paper are: cmp-lg
7
The categories of this paper are: hep-th
23
The categories of this paper are: solv-int
33
The categories of this paper are: plasm-ph
13
The categories of this paper are: quant-ph
17
The categories of this paper are: q-fin
19
The categories of this paper are: eess