= Metallicity dependence of nickel-56 yield
{title2=$X_{56}=1-\frac{27}{11}X_{22}$}
Approximate a fixed <mass> of iron-group freeze-out ashes by nickel-56 and iron-54, with no further weak neutronization and negligible residual light particles. Their electron fractions are $1/2$ and $26/54$. Conservation of the initial <electron fraction in stellar matter>, $1/2-X_{22}/22$, then gives the displayed <nickel> <mass> fraction. Its argument is the initial neon-22 <mass> fraction, which need not equal the earlier <nitrogen> metallicity. The two-isotope mass-budget approximation is not an exact full nuclear equilibrium with all free-particle densities set to zero.
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