ASYMMETRIES IN THE BETA-PICTORIS DUST DISK

Five types of asymmetry are identified and measured in the circumstell ar dust disk of Beta Pictoris using new R-band coronagraphic data. Mod els of axisymmetric dust disks show that the observed tilt of the midp lane may result from a small inclination of the disk to our line of si ght combined with a nonisotropic scattering phase function. The remain ing four asymmetries indicate a nonaxisymmetric distribution of orbiti ng dust particles between 150 and 800 AU projected radius. The disk ma y have been gravitationally perturbed in the past 10(3)-10(4) yr, thou gh a perturbing agent has not been detected. The statistical probabili ty of a stellar close-approach is very small and no field stars have b een uniquely identified as having passed near Beta Pictoris recently. Planets are unlikely candidates due to the large scale of the asymmetr ies, while a brown dwarf search has yielded negative results. (C) 1995 American Astronomical Society.