7.0, & 6.9 $\sigma$ for separation, respectively, and 7.6 & 8.3 $\sigma$ for PA of 2005.4 compared to 1999 and 1994, respectively. (e) The significance for deviation of each separation value from the 2005.4 value is given in the last column (see Fig. 2b). It can be seen as evidence for orbital motion. (d,e) Because the measurements are independent, we can add up the significances (properly) and obtain altogether very high significance against the background hypothesis and $\ge 5 \sigma$ for having detected orbital motion.

To check the errors in separation and/or PA, we not only measured the photocenters of GQ Lup and its companion in the one full final high-S/N image after combining all images of one epoch (one night), but we also measured separation and PA in any of the 15 to 27 GQ Lup images, as well as in [*bins*]{} of 3, 5, 7, and 9 GQ Lup images. With [*bins*]{} of, e.g., $x$ images, we mean here the combination of $x$ individual images by shift+add, e.g., we can obtain three combined images with five individual images added up (or e.g. 5 combined images with 3 individual images added up). We can then determine separation (and PA) 