HIGH-RESOLUTION SPECKLE MASKING OBSERVATIONS OF CERES AND VESTA

We present high-resolution speckle masking observations of the asteroids Ceres and Vesta and a detailed description of the image processing methods applied. The edges of the asteroid disks are reconstructed with high signal-to-noise ratio. On the surface of Ceres very weak surface features are visible. The Vesta image shows high-contrast features. At the time of the observations, Ceres had an apparent angular diameter 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 necessary to develop a new method for the compensation of the four-dimensional 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 function is investigated to study the robustness of the method.