SIMBAD references

A new method is presented to include radiation pressure effects in the modelling of close binaries. The radiative interaction of the binary components increases with T_eff⁴ and the inverse square of reduced separation, and is of particular importance for hot OB-type binaries in close configurations. Since no analytical representation of the modified potential field exists, a numerical procedure was developed to implement radiation pressure. The radiative forces are parametrized using the ratio of radiative relative to gravitational forces as normalizing factor for the calculation of the radiation pressure action on the irradiated photospheres. Both stars are considered in their correct 3D shapes. The local incident flux is obtained by an integration over the visible surface parts of the irradiating component, and the effective radiation pressure action on the irradiated star is determined with respect to the local geometrical conditions (partial shadowing and 3D orientation of the surface). Principal effects of radiation pressure on the shape of the stars and the binary configuration are demonstrated by model calculations. There are several important implications for the binary structure: the geometry of the stellar surfaces is modified; the Lagrangean points are shifted, and the shape and extent of the Roche lobes are changed; the tendency to take up inner contact in L₁ is partly counteracted by radiative forces; outer contact components (with surfaces incorporating L₂ or L₃) may be formed above some critical radiation pressure strength; obvious consequences for the evolution of systems with hot and luminous components like WR or X-ray binaries exist. The modified Roche potential is used as an improved model for the calculation of eclipse light curves, based on the general logistics of the Wilson-Devinney method. The inverse problem is solved by applying the nonlinear simplex parameter optimization algorithm. The feasibility of the new method is demonstrated by photometric solutions of the OB systems IU Aur and AB Cru. The implementation of radiation pressure effects yields improved solutions compared with conventional methods, even in the case of small radiation pressure parameters (e.g. ≤1% for IU Aur). Therefore it appears promising to apply the method to hot O-type systems with non-negligible radiative effects, in order to derive more reliable absolute dimensions for this particularly important group of stars.