almost exactly the same proper motion (which is different from the mean Lupus proper motion, Mugrauer & Neuhäuser 2005), and at the same time not orbiting each other, is exceedingly small. We could also show (in Fig. 2) that the assumption that the two objects are unbound at different parallaxes gives a worse fit (to the observed separation changes) than the assumption that they are at the same distance orbiting each other.\
(iii) The apparent effect could have been introduced by incorrect calibration. We have corrected each original separation and PA measurement for GQ Lup by the individual calibration results from HIP 73357. It could be that pixel scale and/or detector orientation, however, do not change with time, therefore the fact that we measure different values is not real, but just within the noise. However, when plotting separations in pixels (Fig. 2c) or the measured original un-corrected PA in degrees (not shown, but see Table 2), i.e., both without astrometric calibration correction versus time, we still see the same effect, a small decrease in separation and no effect in PA (actually an even larger scatter in PA, so that the individual correction is most likely needed).\
Hence, orbital motion is 