Asymptotic Giant Branch and Supergiant Stellar Diameters in the Mid-infrared

The size of the continuum photospheres of Ori, Her, R Leo, and Cyg have been measured at 11 lm using heterodyne interferometry to accuracies as high as 1%. An assortment of narrow wavelength bands near 11 lm (each having a width 0.17 cm 1) were used to avoid spectral lines. The resulting apparent diameters for Ori and Her are 30% larger than measured near-infrared sizes, whereas the Mira variables, R Leo and Cyg, have 11 lm apparent diameters roughly twice their reported near-infrared sizes. The complexities of interpretation are discussed. Subject headings: infrared: stars — stars: AGB and post-AGB — stars: individual ( Cygni, Herculis, R Leonis, Orionis) — techniques: interferometric