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.
Highlights
The Centaur (10199) Chariklo is a small object in our Solar System moving on an elliptical orbit between Saturn and Uranus, at heliocentric distances varying from 13.1 to 18.9 au
Sicardy et al (2015) observed this system with SPHERE, an adaptive optics system mounted at the 8.2 m Very Large Telescope (VLT/European Southern Observatory (ESO)), and obtained point spread functions (PSFs) of 30–40 mas
In this paper we present the results of eight unpublished stellar occultations by Chariklo and its ring system observed between 2017 and 2020
Summary
The Centaur (10199) Chariklo is a small object in our Solar System moving on an elliptical orbit between Saturn and Uranus, at heliocentric distances varying from 13.1 to 18.9 au. From a stellar occultation observed in 2013, Braga-Ribas et al (2014) reported the discovery of two dense and narrow rings (2013C1R and 2013C2R, hereafter C1R and C2R) surrounding Chariklo at 390 and 405 km from the body centre, respectively. Sicardy et al (2015) observed this system with SPHERE, an adaptive optics system mounted at the 8.2 m Very Large Telescope (VLT/ESO), and obtained point spread functions (PSFs) of 30–40 mas (corresponding to ∼300–400 km at Chariklo’s distance). In this paper we present the results of eight unpublished stellar occultations by Chariklo and its ring system observed between 2017 and 2020 It contains the analysis of three multichord detections of Chariklo’s main body, two multi-chord detections of C1R, and one multi-chord detection of C2R.
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