RV jitter (σ₁) as derived in Bonomo et al. (2017) as a function of log R′_HK activity index calculated in Claudi et al. (2024) for exoplanet host stars with M_⋆ < 1.1 M_⊙. Light-grey error bars denote systems with a baseline shorter than 1 yr, grey error bars are systems with a baseline 1-2 yr, and black error bars are systems with baselines >2 yr. The error bars with arrows are upper limits on the RV jitter. The markers are colour coded with the stellar T_eff. TOI-1438 is marked with a square. The marked systems HAT-P-15, HAT-P-19, TrES-4, and WASP-10 are discussed in Sect. 4.3. Adapted from Fig. 3 in Hekker et al. (2006).