SIMBAD references

Improved light curve solutions and new spectroscopic results for the eclipsing multiple system IU Aur are presented. The early-type binary serves as a test case for the application of a newly developed light curve solution code taking into account the radiation pressure effects caused by the mutual irradiation of the binary components. Improved orbital elements and absolute dimensions are derived. The system is of special interest due to a gravitationally bound third component in a noncoplanar orbit causing a precessional motion of the orbital plane of the close binary. The long-term inclination change with time was investigated by an analysis of the variation of eclipse minimum depths. The nodal rotation period of 335 years and the inclination of the third body orbit are consistent with the theoretically expected values, if a third body mass of 17-18 M_☉ is assumed, which fully complies with the restraints required by the light time orbit. High resolution Coude/CCD spectra were used for an improved determination of the binary mass ratio, which agrees well with the revised photometric solutions. The spectra also allowed for a first spectroscopic detection of the third component. The photometric third light contribution of about 20% and the line strengths of the third body are inconsistent with its mass if ascribed to a single early B-type star. It is therefore suggested that IU Aur is actually not a triple, but a double binary system.