ON THE NATURE OF THE ANOMALOUSLY SLOW APSIDAL MOTION OF DI-HERCULIS

The elliptical three-body problem (a close binary and a nearby companion, three-dimensional case) is examined to elucidate the nature of anomalies in apsidal motion of some close binary systems. The numerical results are presented for once- and twice-averaged problems. It is shown that the significant discrepancy between the observed and the theoretical apsidal motion of DI Her (relativistic and classical effects) possibly results from the close binary orbit perturbations due to a third body.