Upper panels: distribution of close-to-the-plane bulge stars (R_GC ≤ 3.5 kpc, |z| ≤ 0.5 kpc) in the [Mg/Fe] versus [Fe/H] plane. Points are color coded according to their total empirical uncertainty defined as the sum in quadrature of the respective abundance measurement errors. Black squares highlight a subsample of stars for which relatively good-quality distance estimations (also indicating R_GC ≤ 3.5 kpc) are available from the Gaia DR2 Bayesian distance catalog of Bailer-Jones et al. (2018). A shaded vertical area highlights the metallicity range (−0.3 ≤ [Fe/H] ≤ 0.15 dex) in which stars are selected to plot their [Mg/Fe] ratio histogram in the right panel. The best (bimodal) Gaussian mixture, as estimated from an analysis of Gaussian mixture models is displayed with a blue line. Lower panel: Gaussian kernel estimation of the data (open black points) displayed as a density colormap, with a set of density contours as black lines.