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Session 22 - Binary Stars: New Generation Modeling Developments & Results.
Oral session, Tuesday, June 10
North Main Hall F/G,

[22.06] Radiation Pressure Effects on Binary Star Geometry -- with Application to Modeling Binary Stars with Hot Components

H. Drechsel (Remeis Obs. Bamberg)

A method is presented to include radiation pressure effects in the modeling of close binaries. Radiative interaction is particularly important for hot OB-type binary stars in close configurations. The potential field has to be calculated by a numerical approach, since no analytical representation is possible if the Roche potential is accordingly modified. Radiative forces exerted by luminous, hot stars may cause geometric deformations of stellar surfaces and influence the binary configuration and evolution. Principal effects are demonstrated by model calculations accounting for radiation pressure, which is parametrized using the ratio of radiative relative to gravitational forces.

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 is counteracted by radiative forces, while outer contact components (with surfaces incorporating L_2 or L_3) may result above some critical radiation pressure strength; obvious consequences for the evolution of systems with hot and luminous components like Wolf-Rayet or X-ray binaries exist.

The modified Roche potential is used as an improved binary model for the computation of eclipse light curves, based on the Wilson-Devinney technique. The inverse problem is solved by application of the non-linear simplex parameter optimization algorithm. The feasibility of the new method is demonstrated by photometric solutions of a few OB systems. The implementation of radiation pressure effects yields improved light curve representations compared with conventational methods, even in the case of weak radiative forces typical for late O and early B-type stars.

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Program listing for Tuesday