Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: V476 Cyg (Nova Cyg 1920) is currently a dwarf nova -- first such an
  object in the period gap?   V476 Cyg (Nova Cyg 1920) is a bright, fast nova reaching a photographic
magnitude of 2.0. Using the Zwicky Transient Facility (ZTF) public database, I
found that this nova is currently a dwarf nova with a cycle length of ~24 d.
Compared to other classical novae currently in dwarf nova-type states,
outbursts of V476 Cyg are rapidly rising and short with durations of a few
days. Based on the AAVSO observations, this nova was probably already in the
dwarf nova-type phase in 2016, 96 years after the nova eruption. I found a
possible orbital period of 0.1018002(6) d using the ZTF data, which would place
the object in the period gap. This supposed short orbital period appears to
explain the features and faint absolute magnitudes of the observed dwarf nova
outbursts. If this period is confirmed, V476 Cyg is a classical nova with the
shortest orbital period with distinct dwarf nova outbursts and in which a nova
eruption was recorded in the modern era. I also compared with the outburst
properties with V446 Her (Nova Her 1960), which currently shows SS Cyg-type
outbursts. The transition to the dwarf nova-phase in V476 Cyg occurred much
earlier (~100 yr) than what has been supposed (~1000 yr) for classical novae
below the period gap. V476 Cyg would not only provide an ideal laboratory of
the behavior of an irradiated accretion disk in which tidal instability is
expected to work, but also an ideal laboratory of the effect of a massive white
dwarf on dwarf nova outbursts.

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The categories of this paper are: quant-ph
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The categories of this paper are: mtrl-th
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The categories of this paper are: nucl-th
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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: comp-gas
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The categories of this paper are: q-alg
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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: nlin
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The categories of this paper are: q-bio
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The categories of this paper are: gr-qc
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The categories of this paper are: hep-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: patt-sol
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The categories of this paper are: chem-ph