A portrait of Centaur 10199 Chariklo

Abstract

Context. An ESO Large Program was undertaken in October 2006 (P.I.: M. A. Barucci) to provide as complete observations as possible of about 40 Trans-Neptunian Objects and Centaurs, to investigate their surface properties. Hence, new visible and nearinfrared observations of Centaur 10199 Chariklo (1997 CU26)) were performed. Aims. We investigate Chariklo’s surface composition. It has already been suspected of being inhomogeneous. We try to confirm this assumption by comparing our results with previously published works, and find an explanation related the observed variations. Methods. A spectral modeling is applied to the spectra, using different types of mixtures, to place constraints on the amount of water ice present in our new spectrum. Several spectra, obtained at different moments by different groups, are compared by studying the variations in the depth of absorption bands attributable to water ice. The irradiation doses received by Chariklo’s surface are also considered to interpret the observed variations. Results. The presence of water ice is not confirmed by our featureless near-infrared spectra. The main component on the surface, identified by our spectral modeling, is amorphous carbon, which may have been produced by irradiation if Chariklo originated in the transneptunian region. The suspected surface heterogeneity is also confirmed. We show that the variations in Chariklo’s spectral behaviour could be explained by a variation in the number of craters across the surface. Comet-like activity is not detected in our data, though it cannot be excluded.