The effects of non-spherical stellar mass distributions on orbital precession

The precession of the orbits of stars in some systems, such as the binary system DI Herculis, is significantly less than that predicted by general relativity. In this paper we explore possible explanations for this that do not require modifying general relativity. Specifically we have considered the possibility that non-spherical stellar mass distributions can effect precession. To do so we have modelled a star as two adjacent closely spaced masses rather than as a single sphere. We have computed the effect of this on orbital precession both analytically and numerically; both models showed that this non-spherical stellar mass distribution produced retrograde precession. This effect could explain the unexpectedly small observed precession in DI Her without conflicting with the theory of relativity.