Top: evolution of the O/Fe profile. Data are for Cepheids (filled circles, from Luck & Lambert 2011) and for open clusters (Yong et al. 2012, asterisks and Frinchaboy et al. 2013, squares). Dotted curves correspond to model stars of average ages 11, 8, 4 and 0.2 Gyr (from top to bottom) formed in situ and solid curves to stellar populations of the same age found today at radius r. Middle: mass-weighted stellar [O/Fe] profile vs. radius. The solid red curve indicates our results and the shaded area the corresponding ±1σ range. The dashed curves are from Fig. 2 of Gibson et al. (2013) and indicate results of Schönrich & Binney (2009) and Gibson et al. (2013), the latter obtained with two different models (see text). Bottom: the stellar Fe/H gradient of stars found today in the region 5−11 kpc is plotted vs. the average [O/Fe] ratio of those stars (see text).