The detection of a companion star to the Cepheid variable T Monocerotis

Abstract

We have obtained ultraviolet spectra with the International Ultraviolet Explorer (IUE) spacecraft of the classical Cepheid T Mon at several phases in the 27 day period. Significant ultraviolet emission is detected at wavelengths less than 1600 A, where little flux is expected from classical Cepheids. Furthermore, the emission at wavelengths less than about 1900 A does not vary with phase. Comparison with model atmosphere flux distributions shows that the emission is consistent with the flux expected from a companion star with an effective temperature of about 10,000 K (approximately A0) near the main sequence.