Left columns: Time evolution of sin(ϖ − ϖ_p) for each planetesimal. Right columns: Amplitude spectrum obtained with Fast Fourier Transform. The amplitude spectrum is scaled with N/2, where N is the number of data points. Each planetesimal has a different initial semi-major axis, and it is shown in the upper right corner of the panels in the right column divided by the pericenter of the planet q_p = 5 au.