2000ApJ...543..972N

We present mean angular diameters for two Cepheid variables, α UMi and ζ Gem, determined with the Navy Prototype Optical Interferometer (NPOI). We present linear radii for these Cepheids and two additional Cepheids, δ Cep and η Aql, previously observed at the NPOI. We find the limb-darkened angular diameters of α UMi and of ζ Gem to be 3.28±0.02 and 1.55±0.09 mas, respectively. Using trigonometric parallaxes, we find the linear radii of α UMi, ζ Gem, δ Cep, and η Aql to be 46±3, 60⁺²⁵_–14, 45⁺⁸_–6, and 69⁺²⁸_–15 R_☉, respectively. We compare the pulsation periods and linear radii of this sample of Cepheids, which range in period from 3 to 11 days, to theoretical and empirical period-radius and period-radius-mass relations found in the literature. We find that the observed diameter of α UMi is in excellent agreement with the predicted diameter as determined from both surface brightness techniques and theory only if α UMi is a first-overtone pulsator.