Orbital eccentricity, stellar mass, planetary mass and radius, and planet density vs. stellar [Fe/H] (from top to bottom). The horizontal line in the first panel is plotted for e = 0.1, while the vertical dashed lines indicate [Fe/H] = 0.0. The darker dots in the bottom four panels represent stars with e > 0.1. Planet XO-2Sb is shown in the first and third panels, while it is not plotted in the two bottom panels because it is not a transiting planet.