Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Oxygen Recombination in the nebular phase of supernovae 1998bw and
  2002ap   Late-time spectra of stripped-envelope CC-SNe are dominated by strong [O {\sc
i}] $\lambda\lambda$6300,6363 emission, caused by thermal electron excitation
of forbidden [O {\sc i}] transitions. The permitted O
  {\sc i} 7774 \AA\ line is also often observed. This line cannot result from
thermal electron excitation of the oxygen ground state. In this work tests are
performed to verify whether the line can be powered by oxygen recombination
alone, using the examples of two of the best studied type Ic SNe, 1998bw and
2002ap.
  Temperature-dependent effective recombination coefficients for neutral oxygen
are calculated using available atomic data. Missing atomic data are computed in
a temperature range typical for SN nebulae. Core ejecta models for SNe 1998bw
and 2002ap are obtained from modelling their nebular emission spectra so that
oxygen recombination line formation is computed consistently with oxygen
forbidden line emission.
  While SN 2002ap can be explained well by a one dimensional shell model, this
seems not to be possible for SN 1998bw, for which a two dimensional model is
found. At very late epochs the formation of the O {\sc i} 7774 \AA\ line can be
explained by recombination radiation for both SNe, but at earlier epochs strong
absorption is present which may determine the strength of this line even at
$\sim$ 200 days.

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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: comp-gas
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The categories of this paper are: patt-sol
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The categories of this paper are: math-ph
23
The categories of this paper are: solv-int
33
The categories of this paper are: plasm-ph
37
The categories of this paper are: supr-con
31
The categories of this paper are: ao-sci
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The categories of this paper are: hep-th
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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: stat
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The categories of this paper are: physics
1
The categories of this paper are: cs
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The categories of this paper are: dg-ga