Upper plot: time series of the K2-3 RVs extracted with the pipeline TERRA using the HARPS-N spectra. Middle plot: GLS periodogram of the RV time series (red line) is shown. Three levels of p-values are indicated by the horizontal dashed lines. The green dashed line overplotted on the RV periodogram represents the window function of the measurements (bottom plot) shifted in frequency to be superimposed on the strongest peak of the RV periodogram. This helps to identify the alias frequencies of the most relevant peaks. The stellar rotation and planetary orbital frequencies are indicated by vertical lines and corresponding labels.