The Structure of Close Binaries in Two Dimensions

The structure and evolution of close binary stars has been studied using thetwo-dimensional (2D) stellar structure algorithm developed by Deupree (1995).We have calculated a series of solar composition stellar evolution sequences ofbinary models, where the mass of the 2D model is 8Msun with a point-mass 5Msuncompanion. We have also studied the structure of the companion in 2D, byconsidering the zero-age main-sequence (ZAMS) structure of a 5Msun model withan 8Msun point-mass companion. In all cases the binary orbit was assumed to becircular and co-rotating with the rotation rate of the stars. We consideredbinary models with three different initial separations, a = 10, 14 and 20Rsun.These models were evolved through central hydrogen burning or until the moremassive star expanded to fill its critical potential surface or Roche lobe. Thecalculations show that evolution of the deep interior quantities is onlyslightly modified from those of single star evolution. Describing the modelsurface as a Roche equipotential is also satisfactory until very close to thetime of Roche lobe overflow, when the self gravity of the model about to losemass develops a noticeable aspherical component and the surface time scalebecomes sufficiently short that it is conceivable that the actual surface isnot an equipotential.Comment: 22 pages, 10 figures, accepted by Ap