Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Magnetic field and unstable accretion during AM Herculis low states   A study of AM Her low states in September 1990 and 1991 and June-July 1997 is
reported from a coordinated campaign with observations obtained at the
Haute-Provence observatory, at the 6-m telescope of the Special Astrophysical
Observatory and at the 2.6m and 1.25m telescopes of the Crimean observatory.
Spectra obtained at different dates when the source was in low states at a
comparable V magnitude, show the presence of strong Zeeman absorption features
and marked changes in emission lines with a day-to-day reappearance of the HeII
(4686\AA) emission lines in 1991. Despite this variability, the magnetic field
inferred from the fitting of the absorption spectrum with Zeeman hydrogen
splitting, is remarkably constant with a best value of (12.5$\pm$0.5)MG.
Detailed analysis of the UBVRI light curves shows the presence of repetitive
moderate amplitude ($\sim$ 0.3-0.5 mag) flares predominantly red in colour.
These flares are attributed to small accretion events and are compared to the
large ($\sim$ 2 mag.) blue flare reported by Shakhovskoy et al. (1993). We
suggest that the general flaring activity observed during the low states is
generated by accretion events. The different characteristics of the flares
(colour and polarization) are the results of different shock geometries
depending on the net mass accretion flux.

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The categories of this paper are: bayes-an
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The categories of this paper are: patt-sol
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The categories of this paper are: alg-geom
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The categories of this paper are: econ
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The categories of this paper are: quant-ph
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The categories of this paper are: eess
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The categories of this paper are: ao-sci
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The categories of this paper are: adap-org
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The categories of this paper are: q-bio
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The categories of this paper are: comp-gas
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The categories of this paper are: solv-int
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The categories of this paper are: atom-ph
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The categories of this paper are: hep-th
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The categories of this paper are: nucl-th
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The categories of this paper are: funct-an
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The categories of this paper are: cond-mat