Stellar Angular Diameters and Visual Surface Brightness -- II EARLY AND INTERMEDIATE SPECTRAL TYPES

Abstract

The relationship between visual surface brightness and the colour index (V–R) found in Paper I (Barnes & Evans 1976) is considered in greater detail in its applications to early type stars. The expectation that the relationship is independent of luminosity class (which is not the case for (B–V)) is borne out. The validity of the conjecture that the relationship applies to a variable star during its cycle is strengthened. An investigation of the applicability to δ Cep produces an angular diameter curve in excellent phase concordance with the visual light curve and the radial displacement and a mean angular diameter in excellent agreement with stellar atmosphere models. At the present time it is a strain both on the available photometric data and on the precise value of the coefficients in the empirical (F_v, V–R) relationship to apply this to the problem of the determination of Cepheid distances. If the errors can be reduced, the method here proposed could become extremely powerful since it does not suffer from several of the disadvantages of the classical Baade–Wesselink method. It is hoped that this discussion will stimulate other observers to help in the refinement of the method.