Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Active region filaments might harbor weak magnetic fields   Recent spectropolarimetric observations of active region filaments have
revealed polarization profiles with signatures typical of the strong field
Zeeman regime. The conspicuous absence in those observations of scattering
polarization and Hanle effect signatures was then pointed out by some authors.
This was interpreted either as a signature of mixed "turbulent" field
components or as a result of optical thickness. In this article, we present a
natural scenario to explain these Zeeman-only spectro-polarimetric observations
of active region filaments. We propose a two-component model, one on top of the
other. Both components have horizontal fields, the azimuth difference between
them being close to 90 degrees. The component that lies lower in the atmosphere
is permeated by a strong field of the order of 600 G, while the upper component
has much weaker fields, of the order of 10 G. The ensuing scattering
polarization signatures of the individual components have opposite signs, so
that its combination along the line of sight reduces --and even can cancel
out-- the Hanle signatures, giving rise to an apparent only-Zeeman profile.
This model is also applicable to other chromospheric structures seen in
absorption above active regions.

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The categories of this paper are: cs
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The categories of this paper are: quant-ph
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The categories of this paper are: math
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The categories of this paper are: physics
12
The categories of this paper are: nucl-th
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The categories of this paper are: alg-geom
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The categories of this paper are: hep-ph
36
The categories of this paper are: cmp-lg
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The categories of this paper are: hep-lat
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The categories of this paper are: chao-dyn
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The categories of this paper are: bayes-an
34
The categories of this paper are: chem-ph
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The categories of this paper are: gr-qc
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The categories of this paper are: hep-th
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The categories of this paper are: econ
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The categories of this paper are: patt-sol