Asymmetries in the Beta Pictoris Dust Disk

Five types of asymmetry are identified and measured in the circumstellar dust disk of Beta Pictoris using new R-band coronagraphic data. Models of axisymmetric dust disks show that the observed tilt of the midplane may result from a small inclination of the disk to our line of sight combined with a nonisotropic scattering phase function. The remaining four asymmetries indicate a nonaxisymmetric distribution of orbiting dust particles between 150 and 800 AU projected radius. The disk may have been gravitationally perturbed in the past 103-104 yr, though a perturbing agent has not been detected. The statistical probability of a stellar close-approach is very small and no field stars have been uniquely identified as having passed near Beta Pictoris recently. Planets are unlikely candidates due to the large scale of the asymmetries, while a brown dwarf search has yielded negative results.