  The effect of stellar activity on RV appears to be a limiting factor in
detecting Earth-mass planets in the habitable zone of a star similar to the Sun
in spectral type and activity level. It is crucial to estimate if this
conclusion remain true for other stars with current correction methods. We
built realistic time series in RV and chromospheric emission for old
main-sequence F6-K4 stars. The stellar parameters are spectral type, activity
level, rotation period, cycle period and amplitude, latitude coverage, and spot
constrast, which we chose to be in ranges that are compatible with our current
knowledge. This very large set of synthetic time series allowed us to study the
effect of the parameters on the RV jitter and how the different contributions
to the RV are affected in this first analysis of the data set. The RV jitter
was used to provide a first-order detection limit for each time series and
different temporal samplings. We find that the coverage in latitude of the
activity pattern and the cycle amplitudes have a strong effect on the RV
jitter, as has stellar inclination. RV jitter trends with B-V and LogR'HK are
similar to observations, but activity cannot be responsible for RV jitter
larger than 2-3 m/s for very quiet stars: this observed jitter is therefore
likely to be due to other causes. We show that based on the RV jitter that is
associated with each time series and using a simple criterion, a planet with
one Earth mass and a period of one to two years probably cannot be detected
with current analysis techniques, except for the lower mass stars in our
sample, but many observations would be required. The effect of inclination is
critical. The results are very important in the context of future RV follow-ups
of transit detections of such planets. A significant improvement of analysis
techniques and/or observing strategies must be made to reach such low detection
limits.
