Size and shape of the trans-Neptunian object (470316) 2007 OC10: Comparison with thermal data

¹ Instituto de Astrofísica de Andalucía, Glorieta de la Astronomía S/N, 18008 Granada, Spain
² Florida Space Institute, UCF, 12354 Research Parkway, Partnership 1 Building, Room 211, Orlando, FL, USA
³ Centro Astronómico Hispano en Andalucía, Observatorio de Calar Alto, Sierra de los Filabres, 04550 Gérgal, Almeria, Spain
⁴ LESIA, Observatoire de Paris, Université PSL, Sorbonne Université, Université de Paris, CNRS, 92190 Meudon, France
⁵ Federal University of Technology-Paraná (UTFPR/PPGFA), Curitiba, PR, Brazil
⁶ Laboratório Interinstitucional de e-Astronomia – LIneA – and INCT do e-Universo, Av. Pastor Martin Luther King Jr, 126 – Del Castilho, Nova América Offices, Torre 3000/sala 817, Rio de Janeiro, RJ 20765-000, Brazil
⁷ Instituto de Astrofísica de Canarias (IAC), C/Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
⁸ Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna (S.C. Tenerife), Spain
⁹ Istanbul University, Faculty of Science, Department of Astronomy and Space Sciences, 34116, Beyazıt, Istanbul, Türkiye
¹⁰ Istanbul University Observatory Application and Research Center, 34116 Istanbul, Türkiye
¹¹ Oukaimeden Observatory, High Energy Physics and Astrophysics Laboratory, FSSM, Cadi Ayyad University, Marrakech, Morocco
¹² Department of Earth, Atmospheric and Planetary Science, Massachusetts Institute of Technology, Cambridge, MA, USA
¹³ Grupo de Ocultaciones de Zaragoza, Spain
¹⁴ The American Association of Variable Star Observers (AAVSO), 185 Alewife Brook Parkway, Suite 410, Cambridge, MA 02138, USA
¹⁵ Agrupación Astronómica de Sabadell, Prat de la Riba sn, 08206 Sabadell, Spain
¹⁶ INAF – Catania Astrophysical Observatory, via S. Sofia 78, 95123 Catania, Italy
¹⁷ Centro de Estudios de Física del Cosmos de Aragón, Plaza San Juan 1, 44001 Teruel, Spain
¹⁸ Observatorio Astronómico de la Universidad de Valencia, 46980 Paterna, Valencia, Spain
¹⁹ School of Physics and Astronomy and Wise Observatory, Tel-Aviv University, Tel-Aviv 6997801, Israel
²⁰ Observatorio de Albox, Almeria, Spain
²¹ Observatorio Astronómico de Guirguillano, Plaza Consistorial 6, 31291 Guirguillano, Spain
²² GAL Hassin – Centro Internazionale per le Scienze Astronomiche, Via della Fontana Mitri, 90010 Isnello, Palermo, Italy
²³ International Occultation Timing Association – European Section (IOTA/ES), Am Brombeerhag 13, 30459 Hannover, Germany
²⁴ Observatorio El Guijo (MPC J27), Galapagar, Madrid, Spain
²⁵ Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (IEEC-UB), Carrer de Martí i Franquès, 1, 08028 Barcelona, Spain
²⁶ Departamento de Fisica, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante, Carr. de San Vicente del Raspeig, s/n, 03690 San Vicente del Raspeig, Alicante, Spain

^★ Corresponding author: jgomez@iaa.es

Received: 20 December 2024
Accepted: 9 March 2025

Abstract

Context. The shapes of only 12 trans-Neptunian objects have been directly measured, offering crucial insights into their internal structure. These properties are strongly connected to the processes that shaped the early Solar System, and provide important clues about its evolution.

Aims. The aim of the present work is to characterise the size, shape, geometric albedo, and beaming parameter of the TNO (470316) 2007 OC10. We compared these values to the effective diameter and geometric albedo obtained from thermal data by the TNOs are Cool survey. We also combined occultation and thermal data to constrain the size of a putative unresolved satellite.

Methods. We predicted an occultation of the star Gaia DR3 2727866328215869952 by 2007 OC10 on 2022 August 22. Four stations detected the occultation. We implemented an elliptical shape model for the projection of 2007 OC10. Following a Bayesian approach, we obtained the posterior probability density in the model parameter space using a Markov chain Monte Carlo method.

Results. The elliptical limb of 2007 OC 10 has semi-axes of 215_-7⁺¹⁰ × 141_-23⁺²⁴ km, and thus the projected axis ratio is b/a = 0.58_-0.16^+0.16. The area-equivalent diameter is 330_-55⁺⁵⁶ km. From our own absolute magnitude value of H_V = 5.40 ± 0.02, the geometric albedo is p_V = 11.2_-5.0^+2.1%. Combining the occultation results with thermal data, we constrain the beaming parameter to η = 1.42_-0.58^+0.75. Occultation data reveal that the star is double. The secondary star has a position angle with respect to the primary of 56_-17⁺³ degrees, has an angular separation of 57_-11⁺⁴ mas, and is 1.18_-0.07^+0.07 magnitudes fainter than the primary.