Minimum S/N required to detect a range of R_FeII and combinations. The blue grid indicates the range of the parameter space covered in the simulation described in Sect. 9.1.2. Points on the grid that do not have a minimum S/N indicator represent R_FeII and combinations that are not detectable even at the highest S/N used in this experiment. Sources detected at these R_FeII and combinations are likely to be spurious (see Fig. 17).