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The ever increasing level of precision achieved by present and futureradial-velocity instruments is opening the way to discovering very low-mass,long-period planets (e.g. solar-system analogs). These systems will bedetectable as low-amplitude signals in radial-velocity (RV). However, animportant obstacle to their detection may be the existence of stellar magneticcycles on similar timescales. Here we present the results of a long-termprogram to simultaneously measure radial-velocities and stellar-activityindicators (CaII, H_alpha, HeI) for a sample of stars with known activitycycles. Our results suggest that all these stellar activity indexes can be usedto trace the stellar magnetic cycle in solar-type stars. Likewise, we findclear indications that different parameters of the HARPS cross-correlationfunction (BIS, FWHM, and contrast) are also sensitive to activity levelvariations. Finally, we show that, although in a few cases slight correlationsor anti-correlations between radial-velocity and the activity level of the starexist, their origin is still not clear. We can, however, conclude that for ourtargets (early-K dwarfs) we do not find evidence of any radial-velocityvariations induced by variations of the stellar magnetic cycle with amplitudessignificantly above ~1 m/s.

Do stellar magnetic cycles influence the measurement of precise radial velocities?