Predicting Stellar Angular Sizes

Abstract

Reliable prediction of stellar diameters, particularly angulardiameters, is a useful and necessary tool for the increasing number ofmilliarcsecond resolution studies being carried out in the astronomicalcommunity. A new and accurate technique of predicting angular sizes ispresented for main-sequence stars, giant and supergiant stars, and moreevolved sources such as carbon stars and Mira variables. This techniqueuses observed K and either V or B broadband photometry to predict V=0 orB=0 zero-magnitude angular sizes, which are then readily scaled to theapparent angular sizes with the V or B photometry. The spread in therelationship is 2.2% for main-sequence stars, 11%-12% for giant andsupergiant stars, and 20%-26% for evolved sources. Compared to othersimple predictions of angular size, such as linear radius-distancemethods or blackbody estimates, zero-magnitude angular size predictionscan provide apparent angular sizes with errors that are 2-5 timessmaller.