Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Variability of Fe II Emission Features in the Seyfert 1 Galaxy NGC 5548   We study the low-contrast Fe II emission blends in the ultraviolet
(1250--2200A) and optical (4000--6000A) spectra of the Seyfert 1 galaxy NGC
5548 and show that these features vary in flux and that these variations are
correlated with those of the optical continuum. The amplitude of variability of
the optical Fe II emission is 50% - 75% that of Hbeta and the ultraviolet Fe II
emission varies with an even larger amplitude than Hbeta. However, accurate
measurement of the flux in these blends proves to be very difficult even using
excellent Fe II templates to fit the spectra. We are able to constrain only
weakly the optical Fe II emission-line response timescale to a value less than
several weeks; this upper limit exceeds all the reliably measured emission-line
lags in this source so it is not particularly meaningful. Nevertheless, the
fact that the optical Fe II and continuum flux variations are correlated
indicates that line fluorescence in a photoionized plasma, rather than
collisional excitation, is responsible for the Fe II emission. The iron
emission templates are available upon request.

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The categories of this paper are: comp-gas
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The categories of this paper are: math-ph
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The categories of this paper are: funct-an
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The categories of this paper are: gr-qc
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The categories of this paper are: nucl-th
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The categories of this paper are: solv-int
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The categories of this paper are: nucl-ex
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The categories of this paper are: math
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The categories of this paper are: econ
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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: alg-geom
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The categories of this paper are: nlin
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The categories of this paper are: hep-ph
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The categories of this paper are: supr-con
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The categories of this paper are: q-fin