Explanation of the spectro-astrometric signals detected towards VW Cha. VW Cha forms a triple system (Fig. 2 in Correia et al. 2006). The constituents A and B are separated by 0″.65 at P.A. 177°, that is, aligned with slit position 1 of this study. The constituents B and C are separated by 0″.11 at P.A. 233°. In the three observations the 0″.6 wide UVES slit (thick solid lines) covers all three components of VW Cha. The photocentre of VW Cha (marked as thick dashed line) lies in between A and B+C depending on the slit orientation and the brightnesses of A, B, and C. The detected different spectro-astrometric offsets with respect to the photocentre are therefore an effect of the slit orientation.