2000ApJ...534L.105S

We study stars in the Lick planetary survey for correlations between simultaneous measurements of high-precision radial velocities v_r and magnetic activity (as measured in an S_IR emission index from Ca II λ8662). We find significant correlations in ~30% of the stars. After removing linear trends between S_IR and v_r, we find that the dispersion in v_r in these stars is decreased by an average of 17%, or ~45% of the dispersion above the measurement noise. F stars and less active stars with variable Ca II H and K lines are the most successfully corrected. The magnitude of the slope of the S_IR versus v_r relations increases proportional to vsini and (excepting M dwarfs) tends to decrease with decreasing T_eff. We argue that the main cause of these effects is modification of the mean line bisector shape brought on by long-term, magnetic activity-induced changes in the surface brightness and convective patterns. The correlations can be used to partially correct v_r data for the effects of long-term activity variations, potentially permitting study of planets around some (higher mass) younger stars and planets producing smaller stellar reflex velocities.