Results from a stellar occultation by KBO Varda

We present results obtained from a stellar occultation by the classical Kuiper belt object (174567) Varda on 10 September 2018. Varda is a known binary system and among the largest TNOs known today, but has not been studied during an occultation before. Among our collaborators, 24 stations were able to acquire data at the time of the event, of which 15 obtained a clear detection, making this the best-sampled occultation of a TNO to date. As potential stellar duplicity could cause a significant shift of the ground path, we studied the target star in advance through speckle imaging with 'Alopeke at Gemini North. The reconstructed shape is an ellipsoid, which supports Varda's status as a dwarf planet candidate. Albeit slightly smaller, the calculated size is in agreement with the radiometric diameter based on Herschel/PACS FIR measurements. Post-event analysis of the dataset obtained at DCT revealed a faint, unresolved companion or background star very close to the target, which was well under the detection limit of our speckle imager data, but had practically no effect on the predicted path. No atmosphere has been detected. The occultation helped to constrain size and albedo, which in turn helps to better constrain Varda's density.