Stars in the sample plotted in the [Mg/Fe]-[Fe/H] plane. The lines show the division into high- and low-α components. A buffer zone 0.01dex either side of the lines (i.e. 0.02 dex total) was discarded from the separated samples to avoid population cross-contamination. There is faint evidence of clustering in the high-α disk which is more prominent in the [C/Fe]-[Fe/H] plane as show in Fig. 4