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The radial velocity signature of stellar noise is small, around themeter-per-second, but already too much for the detection of Earth mass planetsin habitable zones. In this paper, we address the important role played byobservational strategies in averaging out the radial velocity signature ofstellar noise. We also derive the planetary mass detection limits expected inpresence of stellar noise. We start with HARPS asteroseismology measurementsfor 4 stars (beta Hyi, alpha Cen A, mu Ara and tau Ceti) available in the ESOarchive plus very precise measurements of alpha Cen B. This sample coversdifferent spectral types, from G2 to K1 and different evolutionary stage, fromsubgiant to dwarf stars. Since the span of our data ranges between 5 to 8 days,we will have access to oscillation modes and granulation phenomena, withoutimportant contribution of activity noise which is present at larger timescales. For those 5 stars, we generate synthetic radial velocity measurementsafter fitting corresponding models of stellar noise in Fourier space. Thesemeasurements allows us to study the radial velocity variation due to stellarnoise for different observational strategies as well as the correspondingplanetary mass detection limits. Applying 3 measurements per night of 10minutes exposure each, 2 hours apart, seems to average out most efficiently thestellar noise considered. For quiet K1V stars as alpha Cen B, such a strategyallows us to detect planets of ~3 times the mass of Earth with an orbitalperiod of 200 days, corresponding to the habitable zone of the star. Sinceactivity is not yet included in our simulation, these detection limitscorrespond to a case, which exist, where the host star has few magneticfeatures. In this case stellar noise is dominated by oscillation modes andgranulation phenomena.

Planetary detection limits taking into account stellar noise. I. Observational strategies to reduce stellar oscillation and granulation effects