Observational determination of the gravity darkening exponent and bolometric albedo for close binary star systems

Abstract

A group of close binary star systems, analysed by the Wilson–Devinney Method, provide observationally determined values for the gravity darkening exponent and the bolometric albedo. Stars with radiative envelopes were found to have an average value of <it>g</it><inf>rad</inf> = 0.96 and an average value of <it>A</it><inf>rad</inf> = 1.02, while stars with convective envelopes gave an average value of <it>g</it><inf>conv</inf> = 0.31 and an average value of <it>A</it><inf>conv</inf> = 0.56. For a subgroup composed exclusively of A and W-type W UMa systems, the A-types were found to have a slightly lower average value of <it>g</it><inf>A</inf> = 0.28, while the W-type binaries were found to have both higher average values of <it>g</it><inf>W</inf> = 0.37, and a temperature differential of several hundred degrees, with the secondary being the hotter component.