The angular diameter of R Doradus: a nearby Mira-like star

We find the angular diameter of R Doradus to be 57+/-5mas, exceeding that of Betelgeuse and implying that R Dor is larger in apparent size than every star except the Sun. R Dor is shown to be closely related to the Mira variables. We estimate an effective temperature of 2740+/-190K, a distance of 61+/-7pc, a luminosity of 6500+/-1400 Lsolar and a radius of 370+/-50 Rsolar. The characteristics of R Dor are consistent with it being near the edge of a Mira instability strip. We detect non-zero closure phases from R Dor, indicating an asymmetric brightness distribution. We also observed W Hydrae, a small-amplitude Mira, for which we find an angular diameter of 44+/-4mas.