  Context. RU Lup is a Classical T Tauri star with unusually strong emission
lines, which has been interpreted as manifestations of accretion. Recently,
evidence has accumulated that this star might have a variable radial velocity.
Aims. We intended to investigate in more detail the possible variability in
radial velocity using a set of 68 high-resolution spectra taken at the VLT
(UVES), the AAT (UCLES) and the CTIO (echelle). Methods. Using standard
cross-correlation techniques, we determined the radial velocity of RU Lup. We
analysed these results with Phasedispersion minimization and the Lomb-Scargle
periodogram and searched for possible periodicities in the obtained radial
velocities. We also analysed changes in the absorption line shapes and the
photometric variability of RU Lup. Results. Our analysis indicated that RU Lup
exhibits variations in radial velocity with a periodicity of 3.71 days and an
amplitude of 2.17 km/s. These variations can be explained by the presence of
large spots, or groups of spots, on the surface of RU Lup. We also considered a
low-mass companion and stellar pulsations as alternative sources for these
variations but found these to be unlikely.
