The Effects of Limb Darkening on Measurements of Angular Size with an Intensity Interferometer

Abstract

The correlation curve measured with an intensity interferometer has a shape out to its first minimum which is insensitive to the brightness distribution across a star. Observations are therefore initially interpreted in terms of the angular diameter of an equivalent uniform disc. The necessary correction to obtain the true limb-darkened angular diameter may be made by means of an approximate formula and a limb-darkening coefficient µ λ . More precise corrections, used in analysing the results from Narrabri Observatory, are given for a grid of model stellar atmospheres and these are compared with those given by the approximate formula. Observations of the secondary maximum of the correlation curve for Sirius are reported and compared with predictions based on a model atmosphere.