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The effect of stellar activity on RV appears to be a limiting factor indetecting Earth-mass planets in the habitable zone of a star similar to the Sunin spectral type and activity level. It is crucial to estimate if thisconclusion remain true for other stars with current correction methods. Webuilt realistic time series in RV and chromospheric emission for oldmain-sequence F6-K4 stars. The stellar parameters are spectral type, activitylevel, rotation period, cycle period and amplitude, latitude coverage, and spotconstrast, which we chose to be in ranges that are compatible with our currentknowledge. This very large set of synthetic time series allowed us to study theeffect of the parameters on the RV jitter and how the different contributionsto the RV are affected in this first analysis of the data set. The RV jitterwas used to provide a first-order detection limit for each time series anddifferent temporal samplings. We find that the coverage in latitude of theactivity pattern and the cycle amplitudes have a strong effect on the RVjitter, as has stellar inclination. RV jitter trends with B-V and LogR'HK aresimilar to observations, but activity cannot be responsible for RV jitterlarger than 2-3 m/s for very quiet stars: this observed jitter is thereforelikely to be due to other causes. We show that based on the RV jitter that isassociated with each time series and using a simple criterion, a planet withone Earth mass and a period of one to two years probably cannot be detectedwith current analysis techniques, except for the lower mass stars in oursample, but many observations would be required. The effect of inclination iscritical. The results are very important in the context of future RV follow-upsof transit detections of such planets. A significant improvement of analysistechniques and/or observing strategies must be made to reach such low detectionlimits.

Activity time series of old stars from late F to early K. II. Radial velocity jitter and exoplanet detectability