Context :

Aims : We study the physical characteristics ( shape , dimensions , spin axis direction , albedo maps , mineralogy ) of the dwarf-planet Ceres based on high-angular resolution near-infrared observations .

Methods : We analyze adaptive optics J/H/K imaging observations of Ceres performed at Keck II Observatory in September 2002 with an equivalent spatial resolution of \sim 50 km .
The spectral behavior of the main geological features present on Ceres is compared with laboratory samples .

Results : Ceres ’ shape can be described by an oblate spheroid ( a = b = 479.7 \pm 2.3 km , c = 444.4 \pm 2.1 km ) with EQJ2000.0 spin vector coordinates \alpha _ { 0 } = 288 \degr \pm 5 \degr and \delta _ { 0 } = +66 \degr \pm 5 \degr .
Ceres sidereal period is measured to be 9.074 10 _ { -0.000 14 } ^ { +0.000 10 } h. We image surface features with diameters in the 50-180 km range and an albedo contrast of \sim 6 % with respect to the average Ceres albedo .
The spectral behavior of the brightest regions on Ceres is consistent with phyllosilicates and carbonate compounds .
Darker isolated regions could be related to the presence of frost .

Conclusions :