Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Electron Captures on $^{14}{\rm N}$ as a Trigger for Helium Shell
  Detonations   White dwarfs (WDs) that accrete helium at rates $\sim 10^{-8} \, M_\odot \,
\rm yr^{-1}$, such as those in close binaries with sdB stars, can accumulate
large ($\gtrsim 0.1 \, M_\odot$) helium envelopes which are likely to detonate.
We perform binary stellar evolution calculations of sdB+WD binary systems with
MESA, incorporating the important reaction chain $^{14}{\rm N}(e^-, \nu)
{^{14}{\rm C}} ( \alpha, \gamma) {^{18}{\rm
  O}}$ (NCO), including a recent measurement for the ${^{14}{\rm C}} ( \alpha,
\gamma) {^{18}{\rm O}}$ rate. In large accreted helium shells, the NCO reaction
chain leads to ignitions at the dense base of the freshly accreted envelope, in
contrast to $3\alpha$ ignitions which occur away from the base of the shell. In
addition, at these accretion rates, the shells accumulate on a timescale
comparable to their thermal time, leading to an enhanced sensitivity of the
outcome on the accretion rate history. Hence, time dependent accretion rates
from binary stellar evolution are necessary to determine the helium layer mass
at ignition. We model the observed sdB+WD system ${\rm CD}\,-30^\circ 11223$
and find that the inclusion of these effects predicts ignition of a $0.153 \,
M_\odot$ helium shell, nearly a factor of two larger than previous predictions.
A shell with this mass will ignite dynamically, a necessary condition for a
helium shell detonation.

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The categories of this paper are: math-ph
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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: alg-geom
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The categories of this paper are: acc-phys
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The categories of this paper are: cmp-lg
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The categories of this paper are: q-fin
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The categories of this paper are: chao-dyn
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The categories of this paper are: hep-lat
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The categories of this paper are: atom-ph
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The categories of this paper are: nucl-ex
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The categories of this paper are: physics
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The categories of this paper are: dg-ga
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The categories of this paper are: bayes-an
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The categories of this paper are: chem-ph
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The categories of this paper are: eess