Danchi,bester,hale,2

Visibility observations at 11 km of o Ceti have been made with the University of California (Berkeley) Infrared Spatial Interferometer during the time period 1988È1995. The observed visibilities change dramatically from one epoch to another and are not consistent with simple heating or cooling of the dust with change in luminosity as a function of stellar phase. Instead, large temporal variations in the density of dust within a few stellar radii of the photosphere of o Ceti have occurred. Spherically symmetric models of the dust distribution with two dust shells, one within three stellar radii of the photosphere of the star, the other approximately 10 stellar radii from the star, can account reasonably well for the observed changes. Four types of axially symmetric radiative transfer models were also compared with the dataÈa spherical shell with an ellipsoidal inner cavity, a disk, a spherical shell with one or two inhomogeneities or clumps, and a set of thin partial shells with a Ðxed ..