Cool Stars 14 - Submitted Abstract # 144 This version created on 05 October 2006 Can star spots mimic the long term sinusoidal radial velocity variations observed in red giants? Saskia Hekker, Leiden Observatory Ignas Snellen, Leiden Observatory Andreas Quirrenbach, Landessternwarte Heidelberg, Leiden Observatory Sabine Reffert, Landessternwarte Heidelberg Conny Aerts, Instituut voor Sterrenkunde KUL, University of Nijmegen We have been monitoring radial velocity variations of 180 red giants with a typical precision of 5 to 8 m/s for several years. 35 of these stars show sinusoidal radial velocity variations with typical periods of a few hundred days and amplitudes between 50 and 500 m/s. The photometric variability of these stars as observed by Hipparcos is smaller than 0.06 mag. We investigate whether these radial velocity variations can be explained by the presence of star spots. Therefore we model circular spots on a slowly rotating star and investigate the resultant variations in radial velocity and luminosity. Preliminary results show that the spot model can cause changes in the radial velocity and luminosity comparable to the observed data. In these cases, in order to determine whether the radial velocity variations are intrinsic to the star or caused by a companion, line profile variations need to be investigated. If the skewness of the line profile changes with a frequency comparable to that of the radial velocity variations, the latter are most likely intrinsic to the star. ----------------------------------