Periodograms for four stellar activity indices that show peak powers close to a candidate planet signal detected for four of the stars in this sample. From top to bottom we show the S-activity index periodograms for HIP 18606 and HIP 24275, the Na I index for HIP 90988, and the Hα index for HIP 95124. The green vertical lines mark the positions of candidate planets and the horizontal blue dotted lines show the 0.1% false alarm probabilities. The periods of the strongest peaks are also labelled in each panel.