Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spin down of protostars through gravitational torques   Young protostars embedded in circumstellar discs accrete from an angular
momentum-rich mass reservoir. Without some braking mechanism, all stars should
be spinning at or near break-up velocity. In this paper, we perform simulations
of the self-gravitational collapse of an isothermal cloud using the ORION
adaptive mesh refinement code and investigate the role that gravitational
torques might play in the spin-down of the dense central object. While magnetic
effects likely dominate for low mass stars, high mass and Population III stars
might be less well magnetised. We find that gravitational torques alone prevent
the central object from spinning up to more than half of its breakup velocity,
because higher rotation rates lead to bar-like deformations that enable
efficient angular momentum transfer to the surrounding medium. We also find
that the long-term spin evolution of the central object is dictated by the
properties of the surrounding disc. In particular, spiral modes with azimuthal
wavenumber $m=2$ couple more effectively to its spin than the lopsided $m=1$
mode, which was found to inhibit spin evolution. We suggest that even in the
absence of magnetic fields, gravitational torques may provide an upper limit on
stellar spin, and that moderately massive circumstellar discs can cause
long-term spin down.

34
The categories of this paper are: chem-ph
15
The categories of this paper are: nucl-ex
27
The categories of this paper are: comp-gas
32
The categories of this paper are: atom-ph
7
The categories of this paper are: hep-th
0
The categories of this paper are: hep-ph
22
The categories of this paper are: chao-dyn
31
The categories of this paper are: ao-sci
2
The categories of this paper are: math
8
The categories of this paper are: hep-ex
10
The categories of this paper are: q-bio
16
The categories of this paper are: stat
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
13
The categories of this paper are: quant-ph