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

Authors: N.C. Santos, J. Gomes da Silva, C. Lovis, C. Melo - http://xxx.lanl.gov/abs/0912.2901
Submitted on 15 Dec 2009)

Abstract: The ever increasing level of precision achieved by present and future radial velocity instruments is opening the way to the discovery of very low mass, long period planets (e.g. solar-system analogs). These systems will be detectable as low amplitude signals in radial-velocity (RV). However, an important obstacle to their detection may be the existence of stellar magnetic cycles with similar timescales. Here we present the results of a long term program to measure simultaneously radial-velocities and stellar activity indicators (CaII, H_alpha, HeI) for a sample of stars with known activity cycles. Our results suggest that all these stellar activity indexes can be used to trace the stellar magnetic cycle in solar-type stars. Further to this, we find clear indications that different parameters of the HARPS cross-correlation function (BIS, FWHM, and Contrast) are also sensitive to activity level variations. Finally, we show that though in a few cases slight correlations or anti-correlations between radial-velocity and the activity level of the star exist, their origin is still not clear. We can however conclude that for our targets (early-K dwarfs) we do not find evidence for radial-velocity variations induced by variations of the stellar magnetic cycle with amplitudes significantly above 1 m/s.