a) Periodogram of the primary star RVs of GJ 3861. The highest peak corresponding to a period of 14.855 days is highlighted with the red dot. The 1-day aliases of the best-fit period are highlighted with the red dashed lines. b) HPF RVs of the GJ 3861 binary system. Red and blue points show the RVs of the primary and secondary, respectively. The best-fit model is shown with the red and blue curves for the primary and secondary, respectively. c) Residuals from the best-fit. RV error bars are shown with the best-fit jitter values applied in quadrature.