Upper panel: comparison of our spectroscopically derived  with the β-based computed with Eq. (16). The dashed line indicates the 1:1 relation. The error bar shows a typical uncertainty from our spectroscopic determination, and the uncertainty in , accounting for typical uncertainties in β only. Lower panel: difference of the two log g_F-values for the individual objects, in dex. These quantify the systematic differences from application of our β–log g_F calibration. The dotted lines indicate the 1σ-scatter range.