Flux ratios of OBA stars. The solid and dotted lines represent Cutoff1 and Cutoff2, respectively, while the yellow shaded area designates the region that is populated by very metal-poor stars (see Fig. 3). The color-coding indicates the Galactic Latitude b of each star. As can be seen, most of the stars are located on the Galactic plane (| b |≤ 10°). The orange arrow illustrates the effect of extinction for a color excess E(B − V) ≈ 0.3 mag. The nock and the point of the arrow represent the flux ratios before and after dereddening, respectively.