Size and Shape of Chariklo from Multi-epoch Stellar Occultations

R. Leiva (1) , B. Sicardy (1) , B. Camargo , J. Ortiz , J. Desmars (2, 1) , D. Bérard (1) , E. Lellouch (1) , E. Meza (3) , P. Kervella (1) , C. Snodgrass (4) , R. Duffard (5) , N. Morales , R. Gomes-Júnior , G. Benedetti-Rossi (6) , R. Vieira-Martins (7) , F. Braga-Ribas (7) , M. Assafin (8) , B. Morgado , F. Colas (2) , C. de Witt (9) , A. Sickafoose , H. Breytenbach , J. Dauvergne , P. Schoenau , L. Maquet (2) , L. Bath , J. Bode , A. Cool , B. Lade (10) , S. Kerr (11) , D. Herald (12)

1 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
2 IMCCE - Institut de Mécanique Céleste et de Calcul des Ephémérides
3 LESIA (UMR_8109) - Laboratoire d'études spatiales et d'instrumentation en astrophysique
4 MPS - Max-Planck-Institut für Sonnensystemforschung = Max Planck Institute for Solar System Research
5 IAA - Instituto de Astrofísica de Andalucía
6 Observatorio Nacional [Rio de Janeiro]
7 Observatório Nacional/MCT
8 Observatório do Valongo/UFRJ [Rio de Janeiro]
9 Springbok
10 Stockport Observatory
11 AAQ - Astronomical Association of Queensland
12 Canberra Astronomical Society

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}<SUB>-6</SUB><SUP> 3</SUP> {km} and c={96}<SUB>-4</SUB><SUP> 14</SUP> {km}, respectively, with density {970}<SUB>-180</SUB><SUP> 300</SUP> {kg} {{{m}}}<SUP>-3</SUP>. The ellipsoidal model has semiaxes a={148}<SUB>-4</SUB><SUP> 6</SUP> {km}, b={132}<SUB>-5</SUB><SUP> 6</SUP> {km}, and c={102}<SUB>-8</SUB><SUP> 10</SUP> {km}. Finally, the Jacobi model has semiaxes a = 157 ± 4 km, b = 139 ± 4 km, and c = 86 ± 1 km, and density {796}<SUB>-4</SUB><SUP> 2</SUP> {kg} {{{m}}}<SUP>-3</SUP>. 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<SUP>18</SUP> kg places the rings close to 3:1 resonance between the ring mean motion and Chariklo's rotation period.

Domaines: Physique [physics]; Astrophysique [astro-ph]

R. Leiva, B. Sicardy, B. Camargo, J. Ortiz, J. Desmars, et al.. Size and Shape of Chariklo from Multi-epoch Stellar Occultations. The Astronomical Journal, 2017, 154 (4), pp.159. ⟨10.3847/1538-3881/aa8956⟩. ⟨hal-02190962⟩