Refined physical parameters for Chariklo’s body and rings from stellar occultations observed between 2013 and 2020^★

¹ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
e-mail: morgado.fis@gmail.com
² Laboratório Interinstitucional de e-Astronomia - LIneA, Rua Gal. José Cristino 77, Rio de Janeiro, 20921-400, Brazil
³ Observatório Nacional/MCTI, R. General José Cristino 77, CEP 20921-400 Rio de Janeiro - RJ, Brazil
⁴ Federal University of Technology - Paraná (UTFPR / DAFIS), Rua Sete de Setembro, 3165, CEP 80230-901, Curitiba, PR, Brazil
⁵ Institut Polytechnique des Sciences Avancées IPSA, 63 boulevard de Brandebourg, 94200 Ivry-sur-Seine, France
⁶ 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
⁷ UNESP - São Paulo State University, Grupo de Dinâmica Orbital e Planetologia, CEP 12516-410, Guaratinguetá, SP, Brazil
⁸ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Bd de l’Observatoire, CS 34229, 06304 Nice Cedex 4, France
⁹ Departamento de Astronomía, Universidad de Chile, Camino del Observatorio 1515, Las Condes, Santiago, Chile
¹⁰ Instituto de Astrofísica de Andalucía, IAA-CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
¹¹ Universidade Federal do Rio de Janeiro - Observatório do Valongo, Ladeira Pedro Antônio 43, CEP 20.080-090 Rio de Janeiro - RJ, Brazil
¹² International Occultation Timing Association / European Section, Am Brombeerhag 13, 30459 Hannover, Germany
¹³ Internationale Amateursternwarte e.V. (IAS), Mittelstrasse 6, 15749 Mittenwalde, Germany
¹⁴ Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3HJ, UK
¹⁵ Florida Space Institute, University of Central Florida, 12354 Research Parkway, Partnership 1, Orlando, FL, USA
¹⁶ BRAMON–Brazilian Meteor Observation Network, Nhandeara, Brazil
¹⁷ Grupo de Matemática Aplicada e Processamento de Sinais, State University of Mato Grosso do Sul - UEMS, Cassilândia, CEP 79540-000, MS, Brazil
¹⁸ IATE-OAC, Universidad Nacional de Córdoba-CONICET, Laprida 854, X5000 BGR, Córdoba, Argentina
¹⁹ Department of Physics, Chemistry and Material Science, University of Namibia, Private Bag 13301, Windhoek, Namibia
²⁰ Centre for Space Research, North-West University, Potchefstroom 2520, South Africa
²¹ Association T60, Observatoire Midi-Pyrénées, 14 avenue Edouard Belin, 31400 Toulouse, France
²² Southwest Research Institute, 1050 Walnut Street, Suite 300, Boulder, CO 80302, USA
²³ Dogsheaven Observatory, SMPW Q25 CJ1 LT10B Brasilia, Brazil
²⁴ Association of Argentine Observatories of Minor Bodies (AOACM)), Argentina
²⁵ Centro de Astronomía (CITEVA), Universidad de Antofagasta, Av. Angamos 601, Antofagasta, Chile
²⁶ Ciel & Espace, Paris, France
²⁷ University of St Andrews, Centre for Exoplanet Science, SUPA School of Physics & Astronomy, North Haugh, St Andrews, KY16 9SS, UK
²⁸ Universidade Estadual de Ponta Grossa (UEPG), Ponta Grossa, Brazil
²⁹ Summit Kinetics Inc, USA
³⁰ Panamanian Observatory in San Pedro de Atacama - OPSPA, San Pedro de Atacama, Chile
³¹ Department of Physics, Southern University of Science and Technology, Shenzhen 518055, PR China
³² Centro Brasileiro de Pesquisas Físicas, Rua Dr Xavier Sigaud 150, Rio de Janeiro 22290-180, Brazil
³³ Trans-Tasman Occultation Alliance (TTOA), Wellington PO Box 3181, New Zealand
³⁴ Association Réunionnaise pour l’Etude du Ciel Austral - ARECA, Sainte-Marie, La Réunion, France
³⁵ Institute of Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87-100, Torun, Poland
³⁶ Department of Astronomy and Space Science, Chungnam National University, 34134 Daejeon, Republic of Korea
³⁷ Observatório SONEAR, Oliveira, Brazil
³⁸ STAR Institute, Université de Liège, Allée du 6 août, 19C, 4000 Liège, Belgium
³⁹ Centre for ExoLife Sciences (CELS), Niels Bohr Institute, øster Voldgade 5, 1350 Copenhagen, Denmark
⁴⁰ Astronomical Association of Queensland, 5 Curtis Street, Pimpama QLD 4209, Australia
⁴¹ Department of Physics and Astronomy, University of North Carolina, Chapel Hill, USA
⁴² Central (Pulkovo) Observatory of the Russian Academy of Sciences, 196140, 65/1 Pulkovskoye Ave., Saint Petersburg, Russia
⁴³ Lowell Observatory, 1400 W Mars Hill Road, Flagstaff, AZ 86001, USA
⁴⁴ Massachusetts Institute of Technology, Department of Earth, Atmospheric and Planetary Sciences, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
⁴⁵ The Astronomical Research Institute, Ashmore, IL, UK
⁴⁶ International Occultation Timing Association (IOTA), PO Box 7152, WA, 98042, USA
⁴⁷ NASA Johnson Space Center Astronomical Society, Houston, TX, USA
⁴⁸ Universidade Estadual do Oeste do Paraná (Unioeste), Avenida Tarquínio Joslin dos Santos 1300, Foz do Iguaçu, PR, 85870-650, Brazil
⁴⁹ Polo Astronômico Casimiro Montenegro Filho/FPTI-BR, Avenida Tancredo Neves 6731, Foz do Iguaçu, PR, 85867-900, Brazil
⁵⁰ San Pedro de Atacama Celestial Explorations - SPACE, Chile
⁵¹ Comisión Nacional de Investigación y Desarrollo Aeroespacial del Perú - CONIDA, Luis Felipe Villarán 1069, San Isidro, Lima, Peru
⁵² Observatorio Astronómico de Moquegua, CP Cambrune, Carumas, Moquegua, Peru
⁵³ Physics and Astronomy Department, Appalachian State University, Boone, NC 28608, USA
⁵⁴ Astrocan Clube de Astronomia Nhandeara, Nhandeara, Brazil
⁵⁵ Centre for mathematical Plasma Astrophysics, Department of Mathematics, KU Leuven, Celestijnenlaan 200B, 3001 Leuven, Belgium
⁵⁶ Centre for Electronic Imaging, Department of Physical Sciences, The Open University, Milton Keynes, MK7 6AA, UK
⁵⁷ Association Des Étoiles pour Tous, 19 Rue Saint Laurent, Maisoncelles, 77320 Saint Martin du Boschet, France
⁵⁸ Observatorio Astronómico Córdoba UNC, Laprida 854, Córdoba, Argentina
⁵⁹ AGORA observatoire des Makes, AGORA, 18 Rue Georges Bizet, Observatoire des Makes, 97421 La Rivière, France
⁶⁰ Institute of Astrophysics, Pontificia Universidad Catolica de Chile, Av. Vicuña Mackenna 4860, Santiago, Chile
⁶¹ Millennium Institute of Astrophysics, Chile
⁶² Centre of Astro-Engineering, Pontificia Universidad Catolica de Chile, Av. Vicuña Mackenna 4860, Santiago, Chile
⁶³ Department of Electrical Engineering, Pontificia Universidad Catolica de Chile, Av. Vicuña Mackenna 4860, Santiago, Chile

Received: 14 June 2021
Accepted: 12 July 2021

Abstract

Context. The Centaur (10199) Chariklo has the first ring system discovered around a small object. It was first observed using stellar occultation in 2013. Stellar occultations allow sizes and shapes to be determined with kilometre accuracy, and provide the characteristics of the occulting object and its vicinity.

Aims. Using stellar occultations observed between 2017 and 2020, our aim is to constrain the physical parameters of Chariklo and its rings. We also determine the structure of the rings, and obtain precise astrometrical positions of Chariklo.

Methods. We predicted and organised several observational campaigns of stellar occultations by Chariklo. Occultation light curves were measured from the datasets, from which ingress and egress times, and the ring widths and opacity values were obtained. These measurements, combined with results from previous works, allow us to obtain significant constraints on Chariklo’s shape and ring structure.

Results. We characterise Chariklo’s ring system (C1R and C2R), and obtain radii and pole orientations that are consistent with, but more accurate than, results from previous occultations. We confirm the detection of W-shaped structures within C1R and an evident variation in radial width. The observed width ranges between 4.8 and 9.1 km with a mean value of 6.5 km. One dual observation (visible and red) does not reveal any differences in the C1R opacity profiles, indicating a ring particle size larger than a few microns. The C1R ring eccentricity is found to be smaller than 0.022 (3σ), and its width variations may indicate an eccentricity higher than ~0.005. We fit a tri-axial shape to Chariklo’s detections over 11 occultations, and determine that Chariklo is consistent with an ellipsoid with semi-axes of 143.8_−1.5^+1.4, 135.2_−2.8^+1.4, and 99.1_−2.7^+5.4 km. Ultimately, we provided seven astrometric positions at a milliarcsecond accuracy level, based on Gaia EDR3, and use it to improve Chariklo’s ephemeris.