Stellar Occultations by Trans-Neptunian Object Satellites: Predictions and Observations

Abstract With the great success of stellar occultations in probing trans-Neptunian objects (TNOs), these observations have become ubiquitous, leading to significant advances in our knowledge of TNOs. As stellar occultation predictions have improved, it has become feasible to predict and observe stellar occultations by satellites of TNOs. In this work, we develop a robust methodology for predicting occultations by large TNO satellites based on the most up-to-date and accurate ephemerides available. We validated our methodology by reproducing several previously recorded occultations by Hi‘iaka, and then used it to predict—and successfully observe—stellar occultations of two other satellites, Namaka and Tinia. As a demonstration of the scientific return of such occultations, we provide the detailed prediction, observation, and analysis of the Tinia occultation. For the satellite of Uni (2002 UX 25 ), we recorded two positive occultation chords that yielded projected circular and elliptical profiles with equivalent diameters of 180.8 ± 0.6 and 193.0 ± 1.0 km, respectively. Using the published absolute magnitude for the system and Tinia’s relative brightness with respect to the primary, we derived an absolute magnitude of H V = 6.476 ± 0.183 mag for Tinia. This corresponds to geometric albedo values of ρ V = 0.139 ± 0.023 and ρ V = 0.122 ± 0.02 for circular and elliptical solutions, respectively. Under the assumption of equal albedos, we obtained a diameter of D = 571 ± 53 km and D = 610 ± 53 km for the primary. Our methods provide a precise, simple, open-source technique for predicting TNO satellite occultations, enabling diverse investigations into the properties of TNOs and their satellites as demonstrated for Tinia.