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

Abstract

The Centaur (10199) Chariklo has the first rings system discovered around a small object. It was first observed using stellar occultation in 2013. Stellar occultations allow the determination of sizes and shapes with kilometre accuracy and obtain characteristics of the occulting object and its vicinity. Using stellar occultations observed between 2017 and 2020, we aim at constraining Chariklo's and its rings physical parameters. We also determine the rings' structure, and obtain precise astrometrical positions of Chariklo. We predicted and organised several observational campaigns of stellar occultations by Chariklo. Occultation light curves were measured from the data sets, from which ingress and egress times, and rings' width and opacity were obtained. These measurements, combined with results from previous works, allow us to obtain significant constraints on Chariklo's shape and rings' structure. 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 confirmed the detection of W-shaped structures within C1R and an evident variation of 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 ring particle's size larger than a few microns. The C1R ring eccentricity is found to be smaller than 0.022 (3-sigma), and its width variations may indicate an eccentricity higher than 0.005. We fit a tri-axial shape to Chariklo's detections over eleven occultations and determine that Chariklo is consistent with an ellipsoid with semi-axes of 143.8, 135.2 and 99.1 km. Ultimately, we provided seven astrometric positions at a milliarcseconds accuracy level, based on Gaia EDR3, and use it to improve Chariklo's ephemeris.

32 pages, 11 Figures in the main text, paper was accepted for publication in Section 10. Planets and planetary systems of Astronomy and Astrophysics on 12/07/2021

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• The two rings of (50000) Quaoar
• SORA: Stellar Occultation Reduction and Analysis
• Constraints on (2060) Chiron's size, shape, and surrounding material from the November 2018 and September 2019 stellar occultations
• Stellar occultations by Trans-Neptunian Objects
• Differential aperture photometry and digital coronagraphy with PRAIA
• Rings around irregular bodies I. Structure of the resonance mesh, applications to Chariklo, Haumea and Quaoar
• Astrometry with PRAIA
• Gravitational disturbance on asteroidal ring systems by close encounter with a small object
• Rings around irregular bodies. II. Numerical simulations of the 1/3 spin-orbit resonance confinement and applications to Chariklo
• Constraining the size, shape, and albedo of the large Trans-Neptunian Object (28978) Ixion with multi-chord stellar occultations