Left: colour-plot showing the equivalent width of the Fe-Kα emission line for varying ṁ_w and v_∞. The darker the shade of green, the larger the equivalent width. The vertical, horizontal solid, and dashed lines correspond to the slices used to extract the curves of growth on the right as a function of ṁ_w/v_∞. Right: curves of growth as a function of ṁ_w (left panel) and v_∞ (right panel). As ṁ_w increases, so does the equivalent width, until eventually the line saturates due to the wind becoming optically thick. Conversely, increasing v_∞ will reduce the equivalent width, as this reduces the overall density of the wind (see Fig. 2) leading to a lower degree of absorption and thus fewer photons available to re-emit as Fe-Kα.