Angular Diameters of the G Subdwarf μ Cassiopeiae A and the K Dwarfs σ Draconis and HR 511 from Interferometric Measurements with the CHARA Array

Using the longest baselines of the CHARA Array, we have measured the angular diameter of the G5 V subdwarf μ Cas A, the first such determination for a halo population star. We compare this result to new diameters for the higher metallicity K0 V stars, σ Dra and HR 511, and find that the metal-poor star, μ Cas A, has an effective temperature (Teff = 5297 ± 32 K), radius (R = 0.791 ± 0.008 R☉), and absolute luminosity (L = 0.442 ± 0.014 L☉) comparable to those of the other two stars with later spectral types. We show that stellar models show a discrepancy in the predicted temperature and radius for μ Cas A, and we discuss these results and how they provide a key to understanding the fundamental relationships for stars with low metallicity.