IUE ultraviolet spectra of the interacting binary U Cep.

Abstract

Twenty-one mid-ultraviolet and three far-ultraviolet spectra of the close interacting binary U Cephei have been obtained with the International Ultraviolet Explorer. The results show that the gas stream leaves the G star, circuits around the B companion some 270 deg and leaves the binary system, confirming the preliminary results. Additional sources of energy, such as the heating arising from the harmonics of nonlinear modes of oscillation or the heating of the G star's hemisphere by the B star, are required to drive the gas stream out of the system. The far-ultraviolet spectra contain the resonance doublet lines of Si IV and C IV. Their strength is comparable to that which is observed in early B stars. It is suggested that these lines arise from the hot pseudophotosphere created by the infalling matter from the gas stream onto the surface of the B star.