The frequency of Cepheid binaries

The authors summarize the methods now available to detect the presence of companions to Cepheids, and then they analyze the results of the application of the recent photometric method proposed by Fernie (1980). If applied to the set of VBLUW observations of southern Cepheids carried out by Pel (1976), this method gives a frequency of about 25%, which is consistent with the more recent spectroscopic determinations (Gieren, 1981). The importance of the IUE satellite to directly observe the U flux emitted by the B-companion is emphasized. (Auth.)