[O/Fe] vs. [Fe/H] in open clusters: NGC 4815 (triangle) and NGC 6705 (square). The curves are the theoretical predictions at three R_GC: 4 kpc (dotted line), 6 kpc (continuous line), and 8 kpc (dashed line), for the model of Magrini et al. (2009, M09; left panel) and the model by Romano et al. (2010, R10; right panel). The theoretical ratios are normalised to the solar abundances predicted by each model.