Predicting Stellar Angular Sizes

Abstract

ABSTRACTReliable prediction of stellar diameters, particularly angular diameters, is a useful and necessary tool for the increasing number of milliarcsecond resolution studies being carried out in the astronomical community. A new and accurate technique of predicting angular sizes is presented for main‐sequence stars, giant and supergiant stars, and more evolved sources such as carbon stars and Mira variables. This technique uses observed K and either V or B broadband 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, 11%–12% for giant and supergiant stars, and 20%–26% for evolved sources. Compared to other simple predictions of angular size, such as linear radius–distance methods or blackbody estimates, zero‐magnitude angular size predictions can provide apparent angular sizes with errors that are 2–5 times smaller.