Evidence for a third component in the U CrB system.

Evidence is found for the presence of a third component orbiting the eclipsing binary U CrB in a highly eccentric 75-year orbit, through the analysis of differences between observed and predicted times of minima over the period 1870-1975. In addition to disproving the explanation of the O-C curve in terms of apsidal rotation, a quasi-periodic, impulsive mass transfer mechanism apparently supported by spectroscopic data is shown to have contradictory results. Possibilities for the photometric, astrometric or spectroscopic confirmation of the postulated third component are discussed.