Xiao et al. (2018) rest-UV emission line ratio evolution as a function of time. Here we show in the left panel C III]/He II λ1640 vs. time and in the right panel O III]λ1666/He II λ1640 vs. time for the BPASS binary models computed with a log₁₀(n_H)=1.0 and U_s = −1.5 and U_s = −3.5 (upper and lower limits of each shaded region, respectively) at different metallicities between 1 Z_⊙ and 1/200th Z_⊙. We only show a limited set of model metallicities for clarity. The black horizontal lines show the line ratios of the MUSE He II λ1640 sample.