Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The detached dust and gas shells around the carbon star U Ant   Context: Geometrically thin, detached shells of gas have been found around a
handful of carbon stars. --Aims: Previous observations of scattered stellar
light in the circumstellar medium around the carbon star U Ant were taken
through filters centred on the resonance lines of K and Na. These observations
could not separate the scattering by dust and atoms. The aim of this paper is
to remedy this situation. --Methods: We have obtained polarization data on
stellar light scattered in the circumstellar medium around U Ant through
filters which contain no strong lines, making it possible to differentiate
between the two scattering agents. Kinematic, as well as spatial, information
on the gas shells were obtained through high-resolution echelle spectrograph
observations of the KI and NaD lines. --Results: We confirm the existence of
two detached shells around U Ant. The inner shell (at a radius of approx 43"
and a width of approx 2") consists mainly of gas, while the outer shell (at a
radius of approx 50" and a width of approx 7") appears to consist exclusively
of dust. Both shells appear to have an over-all spherical geometry. The gas
shell mass is estimated to be 2x10^-3 M(Sun), while the mass of the dust shell
is estimated to be 5x10^-5 M(Sun). The derived expansion velocity, from the KI
and NaD lines, of the gas shell, 19.5 km/s, agrees with that obtained from CO
radio line data. The inferred shell age is 2700 years. There is structure, e.g.
in the form of arcs, inside the gas shell, but it is not clear whether these
are due to additional shells. --Conclusions: Our results support the hypothesis
that the observed geometrically thin, detached shells around carbon stars are
the results of brief periods of intense mass loss, probably associated with
thermal pulses, and subsequent wind-wind interactions.

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The categories of this paper are: mtrl-th
12
The categories of this paper are: nucl-th
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The categories of this paper are: q-fin
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The categories of this paper are: chao-dyn
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The categories of this paper are: solv-int
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The categories of this paper are: hep-lat
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The categories of this paper are: acc-phys
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The categories of this paper are: ao-sci
1
The categories of this paper are: cs
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The categories of this paper are: hep-ph
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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: dg-ga
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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: nlin