[Mg/Fe] vs. [M/H] abundance diagram for the delayed two-infall (upper panel) and the one-infall (lower panel) models for outer galactocentric radii (R = 12 kpc, dash-dotted lines). The stellar yields are from François et al. (2004). The red points are the observed low-α low-metallicity stars ([M/H] < −0.4 dex), whereas the yellow crosses indicate the stars with guiding radius (R_g) larger than 9 kpc.