R.L. acknowledges support from CONICYT-PCHA/Doctorado Nacional/2014-21141198. The authors acknowledge support from the French grant “Beyond Neptune II” ANR-11- IS56-0002. Part of the research leading to these results has received funding from the European Research Council under the European Community’s H2020 (2014-2020/ERC Grant Agreement n° 669416 “LUCKY STAR”). The research leading to these results has received funding from the European Union’s Horizon 2020 Research and Innovation Programme, under Grant Agreement N°. 687378, project SBNAF. E.M. acknowledges support from the Contrato de subvención 205- 2014 Fondecyt—Concytec, Perú. J.I.B.C. acknowledges the CNPq grant n° 308150/2016-3. M.A. thanks the CNPq (Grants 473002/2013-2 and 308721/2011-0) and FAPERJ (Grant E-26/111.488/2013). G.B.-R. acknowledges the support of the CAPES (203.173/2016) and FAPERJ/PAPDRJ (E26/ 200.464/2015-227833) grants. R.V.-M. thanks grants CNPq306885/2013, Capes/Cofecub-2506/2015, Faperj: PAPDRJ45/2013, and E-26/203.026/2015. This work is partly based on observations performed at the MPG 2.2 meter telescope, program CN2016A-87. Based on observations obtained at the SOAR telescope, program SO2015A-015. The 50 cm telescopes used for the Hakos observations belong to the IAS observatory at Hakos/Namibia. This work was partially supported by the National Research Foundation of South Africa and contains data taken at the South African Astronomical Observatory (SAAO). This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC; https:// www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. Facilities: SOAR (SOI), Max Planck:2.2 m (WFI), LNA: BC0.6m. Software: DanDIA (Bramich 2008), IRAF (Tody 1986), emcee (Foreman-Mackey et al. 2013).

We use data from five stellar occultations observed between 2013 and 2016 to constrain Chariklo's size and shape, and the ring reflectivity. We consider four possible models for Chariklo (sphere, Maclaurin spheroid, triaxial ellipsoid, and Jacobi ellipsoid), and we use a Bayesian approach to estimate the corresponding parameters. The spherical model has a radius R = 129 ±3 km. The Maclaurin model has equatorial and polar radii a = b 143 km and c = 96 km, respectively, with density 970 kg m. The ellipsoidal model has semiaxes a = 148 km, b = 132 km, and a = c 102 km. Finally, the Jacobi model has semiaxes a = 157 ±4 km, b = 139 ±4 km, and c = 86 ±1 km, and density . Depending on the model, we obtain topographic features of 6-11 km, typical of Saturn icy satellites with similar size and density. We constrain Chariklo's geometric albedo between 3.1% (sphere) and 4.9% (ellipsoid), while the ring I/F reflectivity is less constrained between 0.6% (Jacobi) and 8.9% (sphere). The ellipsoid model explains both the optical light curve and the long-term photometry variation of the system, giving a plausible value for the geometric albedo of the ring particles of 10%-15%. The derived mass of Chariklo of 6-8 ×10 kg places the rings close to 3:1 resonance between the ring mean motion and Chariklo's rotation period. © 2017. The American Astronomical Society

Leiva, Rodrigo et al.-- Full list of authors: Leiva, R.; Sicardy, B.; Camargo, J. I. B.; Ortiz, J. -L.; Desmars, J.; Bérard, D.; Lellouch, E.; Meza, E.; Kervella, P.; Snodgrass, C.; Duffard, R.; Morales, N.; Gomes-Júnior, A. R.; Benedetti-Rossi, G.; Vieira-Martins, R.; Braga-Ribas, F.; Assafin, M.; Morgado, B. E.; Colas, F.; De Witt, C.; Sickafoose, A. A.; Breytenbach, H.; Dauvergne, J. -L.; Schoenau, P.; Maquet, L.; Bath, K. -L.; Bode, H. -J.; Cool, A.; Lade, B.; Kerr, S.; Herald, D.