[X/Mg] as a function of [Mg/H] with the same symbols as in Fig. 2. The blue lines show least-squares fits to the high-α stars and the red lines show fits to the low-α stars after excluding stars probably associated with the Thamnos substructure (see Fig. 5). On each panel, the atomic species of spectral lines used for deriving abundances and the method of analysis are indicated.