Cumulative histograms of metallicities of all stars and stars harbouring a planet more massive than a given threshold (see top of the figure). The solid black line is the cumulative histogram of all stars considered in this work, which does not depend on the mass of the central star. In each panel, the blue dotted curve is the cumulative histogram of 0.5 M_⊙ stars with a massive planet, the short dashed red line is for 1.0 M_⊙ stars, and the long dashed green curve is for 2.0 M_⊙ stars.