HIGH-RESOLUTION SPECKLE MASKING OBSERVATIONS OF CERES AND VESTA

We present high-resolution speckle masking observations of the asteroi ds Ceres and Vesta and a detailed description of the image processing methods applied. The edges of the asteroid disks are reconstructed wit h high signal-to-noise ratio. On the surface of Ceres very weak surfac e features are visible. The Vesta image shows high-contrast features. At the time of the observations, Ceres had an apparent angular diamete r of 0.74 arcsec (905 km) and Vesta 0.45 arcsec x 0.44 arcsec (539 km x 519 km). For the reconstruction of the asteroid images it was necess ary to develop a new method for the compensation of the four-dimension al photon bias in the average bispectrum of the speckle interferograms . The dependence of the reconstruction on the photon bias compensation and on the compensation of the speckle interferometry transfer functi on is investigated to study the robustness of the method.