  We have measured non-zero closure phases for about 29% of our sample of 56
nearby Asymptotic Giant Branch (AGB) stars, using the 3-telescope Infrared
Optical Telescope Array (IOTA) interferometer at near-infrared wavelengths (H
band) and with angular resolutions in the range 5-10 milliarcseconds. These
nonzero closure phases can only be generated by asymmetric brightness
distributions of the target stars or their surroundings. We discuss how these
results were obtained, and how they might be interpreted in terms of structures
on or near the target stars. We also report measured angular sizes and
hypothesize that most Mira stars would show detectable asymmetry if observed
with adequate angular resolution.
