$^{16}O(p,alpha)^{13}N$ makes explosive oxygen burning sensitive to the metallicity of the progenitors of type Ia supernovae. (arXiv:1907.01158v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Bravo_E/0/1/0/all/0/1">Eduardo Bravo</a>
Even though the main nucleosynthetic products of type Ia supernovae belong to
the iron-group, intermediate-mass alpha-nuclei (silicon, sulfur, argon, and
calcium) stand out in their spectra up to several weeks past maximum
brightness. Recent measurements of the abundances of calcium, argon, and sulfur
in type Ia supernova remnants have been interpreted in terms of
metallicity-dependent oxygen burning, in accordance with previous theoretical
predictions. It is known that $alpha$-rich oxygen burning results from
$^{16}$O$rightarrow^{12}$C followed by efficient $^{12}$C+$^{12}$C fusion
reaction, as compared to oxygen consumption by $^{16}$O fusion reactions, but
the precise mechanism of dependence on the progenitor metallicity has remained
unidentified so far. I show that the chain
$^{16}$O(p,$alpha$)$^{13}$N($gamma$,p)$^{12}$C boosts $alpha$-rich oxygen
burning when the proton abundance is large, increasing the synthesis of argon
and calcium with respect to sulfur and silicon. For high-metallicity
progenitors, the presence of free neutrons leads to a drop in the proton
abundance and the above chain is not efficient. Although the rate of
$^{16}$O(p,$alpha$)$^{13}$N can be found in astrophysical reaction rate
libraries, its uncertainty is unconstrained. Assuming that all reaction rates
other than $^{16}$O(p,$alpha$)$^{13}$N retain their standard values, an
increase by a factor of approximately seven of the $^{16}$O(p,$alpha$)$^{13}$N
rate at temperatures in the order $3-5times10^9$ K is enough to explain the
whole range of calcium-to-sulfur mass ratios measured in Milky Way and LMC
supernova remnants. These same measurements provide a lower limit to the
$^{16}$O(p,$alpha$)$^{13}$N rate in the mentioned temperature range, on the
order of a factor of 0.5 with respect to the rate reported in widely used
literature tabulations.
Even though the main nucleosynthetic products of type Ia supernovae belong to
the iron-group, intermediate-mass alpha-nuclei (silicon, sulfur, argon, and
calcium) stand out in their spectra up to several weeks past maximum
brightness. Recent measurements of the abundances of calcium, argon, and sulfur
in type Ia supernova remnants have been interpreted in terms of
metallicity-dependent oxygen burning, in accordance with previous theoretical
predictions. It is known that $alpha$-rich oxygen burning results from
$^{16}$O$rightarrow^{12}$C followed by efficient $^{12}$C+$^{12}$C fusion
reaction, as compared to oxygen consumption by $^{16}$O fusion reactions, but
the precise mechanism of dependence on the progenitor metallicity has remained
unidentified so far. I show that the chain
$^{16}$O(p,$alpha$)$^{13}$N($gamma$,p)$^{12}$C boosts $alpha$-rich oxygen
burning when the proton abundance is large, increasing the synthesis of argon
and calcium with respect to sulfur and silicon. For high-metallicity
progenitors, the presence of free neutrons leads to a drop in the proton
abundance and the above chain is not efficient. Although the rate of
$^{16}$O(p,$alpha$)$^{13}$N can be found in astrophysical reaction rate
libraries, its uncertainty is unconstrained. Assuming that all reaction rates
other than $^{16}$O(p,$alpha$)$^{13}$N retain their standard values, an
increase by a factor of approximately seven of the $^{16}$O(p,$alpha$)$^{13}$N
rate at temperatures in the order $3-5times10^9$ K is enough to explain the
whole range of calcium-to-sulfur mass ratios measured in Milky Way and LMC
supernova remnants. These same measurements provide a lower limit to the
$^{16}$O(p,$alpha$)$^{13}$N rate in the mentioned temperature range, on the
order of a factor of 0.5 with respect to the rate reported in widely used
literature tabulations.
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