KIWI-GA fit of A13. Top: best-fitting FASTWIND model (solid green line) and 1σ uncertainties (shaded green region) plotted on top of the observed spectrum (black vertical bars representing uncertainties; rebinned for clarity). Bottom: fitness plots for each parameter where darker coloured points represent models of later generations. The solid red line is the best-fit value, and darker and lighter yellow shaded regions represent 1- and 2σ uncertainty regions, respectively.