Size and Shape of Chariklo from Multi-epoch Stellar Occultations*

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 modelhas a radius R = 129 ± 3 km. The Maclaurin model has equatorial and polar radii a=b={143} -6 +3 {km} and c={96} -4 +14 {km}, respectively, with density {970} -180 +300 {kg} {{{m}}} -3 . The ellipsoidalmodel has semiaxes a={148} -4 +6 {km}, b={132} -5 +6 {km}, and c={102} -8 +10 {km}. Finally, the Jacobi model has semiaxes a = 157 ± 4 km, b = 139 ± 4 km, and c = 86 ± 1 km, and density {796} -4 +2 {kg} {{{m}}} -3 . Depending on the model, we obtain topographic features of 6–11 km, typical of Saturnicy satellites with similar size and density. We constrain Chariklo’s geometric albedobetween 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 ellipsoidmodel explains both the optical light curve and the long-term photometry variation of the system, giving a plausible value for the geometric albedoof the ring particles of 10%–15%. The derived mass of Chariklo of 6–8 × 10 18 kg places the rings close to 3:1 resonance between the ring mean motionand Chariklo’s rotation period.