Stellar angular diameters of late-type giants and supergiants measured with the navy prototype optical interferometer

We have measured the angular diameters of 50 F, G, K, and M giant and super giant stars using the Navy Prototype Optical Interferometer at wavelengths between 649 and 850 nm and using three baselines with lengths up to 37.5 m. Uniform-disk diameters, obtained from fits to the visibility amplitude, we re transformed to limb-darkened diameters through the use of limb-darkening coefficients for plane-parallel stellar atmosphere models. These limb-dark ened diameters are compared with those measured with the Mark III optical i nterferometer and with those computed by the infrared flux method. Sources of random and systematic error in the observations are discussed.