Triplet spectrum for different assumptions about the ion temperature and different ionization parameter τ. Left: Case with τ = 10¹¹ cm⁻³ s. The red, blue, and brown curves show T_Z = T_e, T_Z = T_p, and $T_Z=\frac{m_Z}{m_p}\approx 2Z\times T_{\mathrm{p}}$ in a shocked plasma with pure Coulomb energy exchange between species. Right: Case with τ = 9 × 10¹² cm⁻³ s. For this value of τ, T_Z = T_p, but it remains larger than T_e, leading to marginally broader lines. For these large values of τ, the ionization fractions trace the time evolution of T_e, while the ion temperature tracks T_p. As a result, XSPEC reproduces the triplet fluxes for the T_Z = T_p case (blue line) with the BAPEC model using kT = 22 keV (instead of 28 keV) and an extra Gaussian velocity broadening of σ = 180 km s⁻¹. The T_Z = T_e model (red line) is reproduced with the BAPEC model using kT = 22 keV and no velocity broadening.