Radial-velocity and activity index measurements of K2-12. Left panel: HARPS-N radial velocities showing the long-term linear slope due to a companion of yet unknown nature. The Doppler signal of the transiting planet K2-12b (P = 8.28 d) is undetected, hence, only an upper limit to its mass could be given. Right panel: FWHM of the cross-correlation function (top) and CaII S-index (bottom) time series showing no significant linear trends. This would indicate that the radial-velocity linear trend in the left panel is caused by a physically bound companion.