Comparison of spectra for pairs of stars with similar atmospheric parameters (S1/S11 and S8/S14). The top panel displays a zoomed view around the strong Hβ line, revealing virtually identical profiles. The middle panel shows the spectra around the Mg Ib 518.3 nm line. The bottom panel shows the difference between the two spectra. Given the near-identical temperatures, gravities, and metallicities within each pair, the differences in the strengths of the Mg Ib 518.3 line are solely attributed to intrinsic variations in the Mg abundances.