Examples of the stellar activity component in the HARPS-N RV time series (SERVAL, all echelle orders) as fitted through a GP regression using a quasi-periodic kernel (the first and third observing season are shown). The curve in blue represents the GP best-fit model; the grey area is 1σ confidence interval. The RV error bars include a jitter term (11 ms⁻¹) added in quadrature to the measurement uncertainties.