Predicting Stellar Angular Sizes

Reliable prediction of stellar diameters, particularly angular diameters, isa useful and necessary tool for the increasing number of milliarcsecondresolution studies being carried out in the astronomical community. A new andaccurate technique of predicting angular sizes is presented for main sequencestars, giant and supergiant stars, and for more evolved sources such as carbonstars and Mira variables. This technique uses observed $K$ and either $V$ or$B$ broad-band photometry to predict V=0 or B=0 zero magnitude angular sizes,which are then readily scaled to the apparent angular sizes with the $V$ or $B$photometry. The spread in the relationship is 2.2% for main sequence stars; forgiant and supergiant stars, 11-12%; and for evolved sources, results are at the20-26% level. Compared to other simple predictions of angular size, such aslinear radius-distance methods or black-body estimates, zero magnitude angularsize predictions can provide apparent angular sizes with errors that are 2 to 5times smaller.Comment: 28 pages, 4 figures, accepted by PAS