THE INFRARED ANGULAR DIAMETER OF ALPHA HERCULIS MEASURED WITH A MICHELSON INTERFEROMETER

We present the first infrared angular diameter measurements of alpha-Her, a bright cool supergiant. The measurements are the first astronomical scientific results from the infrared Michelson array (IRMA), a prototype near-infrared, broadband, two-telescope interferometer. Here we report on visibilities obtained with telescope separations of 4.8, 8.0, and 12.0 m. The data were fit with both uniform disk and limb darkened models. We find that the uniform disk angular diameter of alpha-Her at 2.2-mu-m is 32.2 +/- 0.8 marcsec. By using the limb darkening models of Sholz & Takeda [A&A, 186, 200 (1987)] and our angular diameter measurement, we have derived a stellar physical angular diameter of 34 +/- 0.8 marcsec. From this determined stellar angular diameter and a compilation of flux measurements from the literature we have further determined that the effective temperature of alpha-Her is 3210 +/- 40 K.