Cumulative histograms of metallicities of all stars and stars with an observable planets. 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 an observed planet, the short dashed red line is for 1.0 M_⊙ stars, and the long dashed green curve is for 2.0 M_⊙ stars. A planet is observable if it produces a RV amplitude larger than a given K, and has a period shorter than 5 years. The different assumed values of K and α_D are indicated at the top and right of the figure. Only planets more massive than the Earth are considered in the figure.