Limb darkening studies with the NPOI

We are now extending the studies of the angular diameters and limb darkening of K giant stars to K supergiants and dwarfs using the Navy Prototype Optical Interferometer (NPOI). Our goal is to compare our diameters with those predicted from model atmosphere calculations. The K supergiants, (epsilon) Peg, (zetz) Cep, and (xi) Cyg, as well as the K2 dwarf, (epsilon) Eri, have been observed with three elements of the astrometric sub-array. The diameters for giants are in good agreement with model predictions; while the results for supergiants agree less well, the extinction corrections make the comparison more uncertain. The measured diameter for (epsilon) Eri is significantly larger than that predicted by the models. These results show the power of the NPOI for testing fundamental astrophysical theory.