Density distribution of our sample stars with S/N > 50 in the T_eff – [Fe/H] (left) and [Fe/H] – [Si/H] (right) planes. In the left panel, the stars in red show the SPB stars of Gebruers et al. (2021), with [Fe/H] from high-resolution spectroscopy (LTE-based). While the T_eff-dependent trend of the [Fe/H] distribution is likely due to NLTE effects, the figure clearly reveals the presence of chemically peculiar stars with super-solar [Fe/H] values, as well as halo BHB stars at the metal-poor end. The right panel shows good consistency between [Si/H] and [Fe/H], verifying the robustness of the determinations (regardless of the systematics due to NLTE). The group of stars with [Fe/H] ~ 0.7 dex and [Si/H] ≳ 1 dex are magnetic ApBp stars, as indicated by their signature enhancement in Si (e.g., Michaud et al. 2015). In the right panel, we omit stars with T_eff < 8000 K because their [Si/H] estimates are found to suffer from larger systematics.