Characterization of dust shell dynamics and asymmetry for six Mira-type stars

Interferometric observations of six Mira-type stars: R Aqr, CIT 3, chi Cyg, W Aql, R Leo, and U Ori are reported. All measurements were made by UC Berkeley's Infrared Spatial Interferometer (ISI), which is comprised of three 1.65 m telescopes using a heterodyne detection system currently operating at 11.15 mu m. All data were taken in a nonredundant east-west linear configuration of telescopes, at a variety of spatial frequencies, with baselines of up to 12 m. By fitting a smooth curve to the closure phase data, as a function of the shortest baseline, the phases of individual visibility measurements can be determined. With curves of the visibility and phase, one-dimensional images are then constructed by an inverse Fourier transform. These images show significant changes in the stars and surrounding dust between the years 2003 and 2004 indicating nonconstant gas emission. They also show significant and varied types of asymmetry, including asymmetries that may be caused by companions, asymmetric stars, or asymmetric dust emission.