Top panel: S/N measurements in circular apertures around the best fit ellipse (orange line) for the K_s -band data from Sect. 5.3.1. The blue apertures contain flux of ring A according to the applied 5σ criterion, whereas the gray apertures reside within the background dominated regime. Bottom panel: S/N within the circular apertures from the top panel, sorted by position angle. The gray and blue areas mark the regimes below and above the 5σ threshold todistinguish background and disk apertures, respectively.