Initial ﹩[\alpha /\mathrm{Fe}]﹩ vs. initial ﹩[\mathrm{Fe}/{\rm{H}}]﹩ for all high signal-to-noise stars in the H3 survey (top), those within 1 kpc from the Galactic plane (middle), and our adopted sample of main-sequence turn-off stars (bottom). All panels clearly show the presence of three distinct components, delineated with colored lines: the metal-poor population with a wide range of ﹩[\alpha /\mathrm{Fe}]﹩ (blue), and the high-α (red) and low-α (orange) populations at high metallicities.