Asymptotic giant branch and supergiant stellar diameters in the mid-infrared

The size of the continuum photospheres of alpha Ori, alpha Her, R Leo, and chi Cyg have been measured at 11 mum using heterodyne interferometry to accuracies as high as 1%. An assortment of narrow wavelength bands near 11 mum( each having a width similar to0.17 cm(-1)) were used to avoid spectral lines. The resulting apparent diameters for alpha Ori and alpha Her are similar to30% larger than measured near-infrared sizes, whereas the Mira variables, R Leo and chi Cyg, have 11 mum apparent diameters roughly twice their reported near-infrared sizes. The complexities of interpretation are discussed.