(a) Lower limit for the ring width that would be detected considering the dispersion of each light curve and the corresponding instrumentation used in this work. Our best constraint is given by Calar Alto’s data (red line). The brown star indicates the lower limit (3.4 km) for a ring that would be detected with an opacity of 50%. (b) Positive and negative chords (as plotted in Fig. 5a) including the negative chord from Calar Alto (red pointed-dashed line) that would have detected the ring system. A similar ring in width to those found in Chariklo and Chiron is plotted in purple with the expected position angle and aspect angle determined from the body pole axis orientation in Fernández-Valenzuela et al. (2017). A ring with larger diameter would be outside the Roche limit for plausible densities of Bienor. The black arrow indicates the motion of the shadow.