SOPHIE velocities and zero-point offset (upper left and lower left panels, respectively) with their corresponding GLS periodograms (right panels). Upper left panel: the solid and dashed curves represent the additional acceleration and secular (projection) acceleration terms under the three models with largest Bayesian evidence. Lower left panel: the thin red line is the spline interpolation of the zero-point shifts measured on a number of standard stars (see text for details), while the points represent the interpolation evaluated at the epochs of the velocity measurements. Right panels: in the periodograms of SOPHIE raw radial velocities of Gl 411 and zero-point offset of the spectrograph, the vertical red lines mark the frequency of the detected periodic signal.