Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Can single O stars produce non-thermal radio emission?   We present a model for the non-thermal radio emission from presumably single
O stars, in terms of synchrotron emission from relativistic electrons
accelerated in wind-embedded shocks. These shocks are associated with an
unstable, chaotic wind. The main improvement with respect to earlier models is
the inclusion of the radial dependence of the shock velocity jump and
compression ratio, based on 1D hydrodynamical simulations. The decrease of the
velocity jump and the compression ratio as a function of radius produces a
rapidly decreasing synchrotron emissivity. This effectively prohibits the
models from reproducing the spectral shape of the observed non-thermal radio
emission. We investigate a number of "escape routes" by which the
hydrodynamical predictions might be reconciled with the radio observations.
Although these escape routes reproduce the observed spectral shape, none of
these escape routes are physically plausible. In particular, re-acceleration by
feeding an electron distribution through a number of shocks, is in
contradiction with current hydrodynamical simulations. These hydrodynamical
simulations have their limitations, most notably the use of 1D. At present, it
is not feasible to perform 2D simulations of the wind out to the distances
required for synchrotron-emission models. Based on the current hydrodynamic
models, we suspect that the observed non-thermal radio emission from O stars
cannot be explained by wind-embedded shocks associated with the instability of
the line-driving mechanism. The most likely alternative mechanism is
synchrotron emission from colliding winds. That would imply that all O stars
with non-thermal radio emission should be members of binary or multiple
systems.

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The categories of this paper are: physics
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The categories of this paper are: q-alg
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The categories of this paper are: nlin
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The categories of this paper are: hep-ex
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The categories of this paper are: math-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: bayes-an
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The categories of this paper are: dg-ga
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The categories of this paper are: supr-con
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The categories of this paper are: alg-geom
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The categories of this paper are: plasm-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: hep-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: adap-org
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The categories of this paper are: mtrl-th