Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Dramatic Spectral Evolution of WZ Sagittae during the 2001 Superoutburst   We carried out optical spectroscopic observations of the most enigmatic dwarf
nova WZ Sge in 11 nights during the 2001 superoutburst. Our observations
covered the period from the initial phase, several hours before the maximum, to
the ninth maximum of the rebrightening phase. The first spectrum shows
absorption lines of H I (except for Halpha), He I, and Na I, as well as
emission lines of He\II, C III/N III, and Halpha in doubly-peaked shapes. The
same spectrum shows the emission lines of C IV and N IV which are the first
detection in dwarf novae. The spectral features dramatically changed in various
time scales. For example, the peak separations of the emission lines of H I and
He II changed from ~700 km/s to 1300 km/s, and one of the peaks dominated over
an orbital period in the genuine-superhump era, but the dominant peak
interchanged with the orbital phase in the early-superhump era. The lines of H
I and He I were in emission at minima of the rebrightening phase (with no
high-excitation lines, nor Na I), while they became in absorption at maxima. We
report on these observational results in detail and their implications
concerning the outburst mechanism, two types of superhumps, and variation of
the disk structure.

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The categories of this paper are: stat
9
The categories of this paper are: nlin
36
The categories of this paper are: cmp-lg
4
The categories of this paper are: cond-mat
37
The categories of this paper are: supr-con
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The categories of this paper are: plasm-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: ao-sci
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The categories of this paper are: patt-sol
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The categories of this paper are: chao-dyn
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The categories of this paper are: nucl-th
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The categories of this paper are: acc-phys
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The categories of this paper are: hep-lat
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The categories of this paper are: cs
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The categories of this paper are: eess
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The categories of this paper are: hep-ex