Toppanel: proper motion in α and δ of the background objects in the IRDIS FoV of HD100546 considering data from May 4, 2015 (filled black), May 29, 2015 (open black), May 31, 2016 (filled red). Dotted points and error bars represent the expected position for a background object. Middle panel: observed time variation of the separation compared with the expected one for a background object. Bottom panel: observed time variation of the position angle compared with the expected one for a background object.