The multichord stellar occultation by the centaur Bienor on January 11, 2019

¹ Florida Space Institute, UCF, 12354 Research Parkway, Partnership 1 building, Room 211, Orlando, USA
e-mail: estela@ucf.edu
² Instituto de astrofísica de Andalucía, CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
³ UNESP – São Paulo State University, Grupo de Dinâmica Orbital e Planetologia, Guaratinguetá, SP 12516-410, Brazil
⁴ Laboratório Interinstitucional de e-Astronomia – LIneA - and INCT do e-Universo, Rua Gal. José Cristino 77, Rio de Janeiro, RJ 20921-400, Brazil
⁵ LESIA, Observatoire de Paris, Université PSL, Sorbonne Université, Université de Paris, CNRS, 92190 Meudon, France
⁶ naXys, University of Namur, 8 Rempart de la Vierge, Namur 5000, Belgium
⁷ Observatorio Nacional (MCTI), Rua Gal. José Cristino, 77 - Bairro Imperial de São Cristóvão, 20921-400 Rio de Janeiro, Brazil
⁸ Complejo Astronómico de La Hita, Camino de Doña Sol, s/n, 45850 LaVilla de Don fadrique, Spain
⁹ Sociedad Astronómica Granadina, Apartado de Correos 195, 18080 Granada, Spain
¹⁰ Software Engineering Department, Andalusian Research Institute in Data Science and Computational Intelligence, University of Granada, Spain
¹¹ Instituto Politécnico de Tomar; CI2 e U.D. Matemática e Física, 2300-313 Tomar, Portugal
¹² Centro Ciência Viva, Alto de Santa Bárbara, Via Galileu Galilei 817, 2250-100 Constância, Portugal
¹³ Centro de Estudios de Física del Cosmos de Aragón, Plaza San Juan 1, 44001 Teruel, Spain
¹⁴ Instituto de Física Aplicada a las Ciencias y las Tecnologías, Universidad de Alicante, San Vicent del Raspeig, 03080 Alicante, Spain
¹⁵ Observatório do Valongo/UFRJ, Ladeira Pedro Antonio 43, Rio de Janeiro, RJ 20.080-090, Brazil
¹⁶ Federal University of Technology-Paraná (UTFPR/DAFIS), Av. Sete de Setembro, 3165, CEP 80230-901 Curitiba, PR, Brazil
¹⁷ Institut Polytechnique des Sciences Avancées IPSA, 63 boulevard de Brandebourg, 94200 Ivry-sur-Seine, France
¹⁸ Institut de Mécanique Céleste et de Calcul des Éphémérides, IMCCE, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, Univ. Lille, 77 Av. Denfert-Rochereau, 75014 Paris, France
¹⁹ Agrupación Astronómica de Sabadell, Carrer Prat de la Riba, 116, 08206 Sabadell, Spain
²⁰ International Occultation Timing Association/European Section, Am Brombeerhag 13, 30459 Hannover, Germany
²¹ Institute of Planetary Research, DLR Rutherfordstr. 2, 12489 Berlin, Germany
²² Albox Observatory, Almería, Spain
²³ Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, 1121 Budapest, Konkoly Thege Miklós út 15−17, Hungary
²⁴ Institute of Space Sciences (ICE, CSIC), Carrer de Can Magrans, s/n, Campus UAB, 08193 Cerdanyola del Vallés (Barcelona), Catalonia, Spain
²⁵ Institut d’Estudis Espacials de Catalunya (IEEC), Edif. Nexus, c/Gran Capità, 2-4, 08034 Barcelona, Catalonia, Spain
²⁶ Agrupación Astronómica de Huesca. Parque Tecnológico Walqa, 13. 22197 Cuarte, Huesca, Spain
²⁷ Observatorio Astronómico Torres de Alcanadre, 22132 Torres de Alcanadre, Spain
²⁸ Observatoire des Baronnies Provençales, Le Mas des Grès, Route de Nyons, 05150 Moydans, France

Received: 27 January 2022
Accepted: 28 October 2022

Abstract

Within our program of physical characterization of trans-Neptunian objects and centaurs, we predicted a stellar occultation by the centaur (54598) Bienor to occur on January 11, 2019, with good observability potential. We obtained high accuracy astrometric data to refine the prediction, resulting in a shadow path favorable for the Iberian Peninsula. This encouraged us to carry out an occultation observation campaign that resulted in five positive detections from four observing sites. This is the fourth centaur for which a multichord (more than two chords) stellar occultation has been observed so far, the other three being (2060) Chiron, (10199) Chariklo, and (95626) 2002 GZ₃₂. From the analysis of the occultation chords, combined with the rotational light curve obtained shortly after the occultation, we determined that Bienor has an area-equivalent diameter of 150 ± 20 km. This diameter is ~30 km smaller than the one obtained from thermal measurements. The position angle of the short axis of the best fitting ellipse obtained through the analysis of the stellar occultation does not match that of the spin axis derived from long-term photometric models. We also detected a strong irregularity in one of the minima of the rotational light curve that is present no matter the aspect angle at which the observations were done. We present different scenarios to reconcile the results from the different techniques. We did not detect secondary drops related to potential rings or satellites. Nonetheless, similar rings in size to that of Chariklo's cannot be discarded due to low data accuracy.