Fe IIIλ5156 to Fe IIλ5169 equivalent-width ratio vs. effective temperature (T_eff). Measurements in theoretical spectra (the nonrotating input grid used by Shokry et al. 2018) are shown as lines for various values of log g (as labeled). The range observed in the inner (narrow line) B star of HR 6819 is shaded in gray. This diagnostic diagram suggests that T_eff lies between 16 and 18 kK. A more precise value is difficult to give owing to blending with the Fe IIλ5169 emission line of the Be star (see Fig. 2).