ADONIS observations of the HD 100546 circumstellar dust disk

We report in this letter the first resolved images of the circumstellar dus t disk around the Pre-Main-Sequence star HD 100546. These near-infrared ima ges were obtained in J and short K bands with the adaptive optics system AD ONIS at the ESO observatory. A bright disk extending 2 arcsec (200 AU) far from the star and viewed with an inclination with respect to the line of si ght around 50 degrees is revealed by the observations. Using a simplified m odel of light scattering, we find that the dust disk density peaks at a dis tance of 40 AU from the star, and the FWHM of this dense ring is typically 20 AU. This type of disk is believed to be a denser precursor of beta Picto ris-like main-sequence disks. The structure of the disk is compared with th e best known example of the class of "debris disks", the disk surrounding b eta Pictoris.