THE ANGULAR DIAMETER OF R-DORADUS - A NEARBY MIRA-LIKE STAR

We find the angular diameter of R Doradus to be 57 +/- 5 mas, exceedin g that of Betelgeuse and implying that R Dor is larger in apparent siz e 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 /- 190 K, a distance of 61 +/- 7 pc, a luminosity of 6500 +/- 1400 L. and a radius of 370 +/- 50 R.. The characteristics of R Dor are consis tent with it being near the edge of a Mira instability strip. We detec t non-zero closure phases from R Dor, indicating an asymmetric brightn ess distribution. We also observed W Hydrae, a small-amplitude Mira, f or which we find an angular diameter of 44 +/- 4 mas.