Theoretical mass ratios of calcium to sulfur (in green) and argon to sulfur (in magenta) from models of detonation of a 1.06 M_⊙ WD, as function of the progenitor metallicity, with either the standard ¹⁶O(p,α)¹³N reaction rate (f₀ = 1) or the rate switched off (f₀ = 0). The argon-to-sulfur mass ratio for Z = 2.25 × 10⁻⁴ is shown as well for several other values of f₀, from bottom to top: f₀ = 0.1, 0.3, and 0.5. The vertical bars on the left of the figure show the range of observational mass ratios derived from measurements of X-ray emission of SNRs (Martínez-Rodríguez et al. 2017).