O–C diagram (with residuals) from linear ephemeris for planet Kepler-539 b (top panel); observations plotted as black points (with error bars) and simulations plotted as open blue circles. Bottom panel shows the RV observations as solid black circles, simulations at the same BJD(UTC) as open blue circles, and the dotted grey line is the RV model for the whole simulation. This the best solution found by trades.