HARPS radial velocities of HIP 12961 phased to the 57.44 days period, overlaid with the adjusted Keplerian orbit (top panel). Residuals from the Keplerian orbit as a function of barycentric Julian day (middle panel), and Lomb-Scargle periodogram of these residuals (bottom panel). The horizontal lines mark false alarm probabilities equivalent to 1, 2 and 3 sigmas significance levels for Gaussian noise.