High-contrast observations of (136108) Haumea: A crystalline water-ice multiple system

7 pages, 4 figures. Accepted for publication in Astronomy and Astrophysics, copyright ESO.International audienceContext. The trans-neptunian region of the Solar System is populated by a large variety of icy bodies showing great diversity in orbital behavior, size, surface color and composition. One can also note the presence of dynamical families and binary systems. One surprising feature detected in the spectra of some of the largest Trans-Neptunians is the presence of crystalline water-ice. This is the case for the large TNO (136 108) Haumea (2003 EL61). Aims. We seek to constrain the state of the water ice of Haumea and its satellites, and investigate possible energy sources to maintain the water ice in its crystalline form. Methods. Spectro-imaging observations in the near infrared have been performed with the integral field spectrograph SINFONI mounted on UT4 at the ESO Very Large Telescope. The spectra of both Haumea and its larger satellite Hi'iaka are analyzed. Relative astrometry of the components is also performed, providing a check of the orbital solutions and equinox seasons. Results. We describe the physical characteristics of the crystalline water-ice present on the surface of Haumea and its largest satellite Hi'iaka and analyze possible sources of heating to maintain water in crystalline state: tidal dissipation in the system components vs radiogenic source. The surface of Hi'iaka appears to be covered by large grains of water ice, almost entirely in its crystalline form. Under some restricted conditions, both radiogenic heating and tidal forces between Haumea and Hi'iaka could provide the energy sufficient to maintain the ice in its crystalline state. Based on observations collected at the European SouthernObservatory, Paranal, Chile - 60.A-923