A Search for Satellite around Ceres
  We conducted a satellite search around the dwarf planet 1 Ceres using Hubble Space Telescope and ground-based Palomar data. No candidate objects were found orbiting Ceres in its entire stability region down to ~500km from the surface of Ceres. Assuming a satellite would have the same albedo as Ceres, which has a visual geometric albedo of 0.07-0.10, our detection limit is sensitive to satellites larger than 1-2 km in diameter. 
A. Bieryla, J. Wm. Parker, E.F. Young, L. A. McFadden, C. T. Russell,   S. A. Stern, M. V. Sykes, B. Gladman
astro-ph.EP