A study of centaur (54598) Bienor from multiple stellar occultations and rotational light curves

Context. Centaurs, distinguished by their volatile-rich compositions, play a pivotal role in understanding the formation and evolution of the early Solar System, as they represent remnants of the primordial material that populated the outer regions. Stellar occultations offer a means to investigate their physical properties, including shape and rotational state, and the potential presence of satellites and rings. Aims. This work aims to conduct a detailed study of the centaur (54598) Bienor through stellar occultations and rotational light curves from photometric data collected during recent years. Methods. We successfully predicted three stellar occultations by Bienor that were observed from Japan, Western Europe, and the USA. In addition, we organized observational campaigns from Spain to obtain rotational light curves. At the same time, we developed software to generate synthetic light curves from three-dimensional shape models, enabling us to validate the outcomes through computer simulations. Results. We resolved Bienor’s projected ellipse for December 26, 2022; determined a prograde sense of rotation; and confirmed an asymmetric rotational light curve. We also retrieved the axes of its triaxial ellipsoid shape as a = (127 ± 5) km, b = (55 ± 4) km, and c = (45 ± 4) km. Moreover, we refined the rotation period to 9.1736 ± 0.0002 h and determined a geometric albedo of (6.5 ± 0.5)%, which is higher than previously determined by other methods. Finally, by comparing our findings with previous results and simulated rotational light curves, we analyzed whether an irregular or contact-binary shape, an additional element such as a satellite, or significant albedo variations on Bienor’s surface may be present.