S-MUS-B REVISITED

IUE high dispersion spectra have been used to investigate the spectral type of the companion of the classical Cepheid S Mus, using Si II and III lines near 1300 Angstrom. In addition, the energy distribution fr om 1200 to 3200 Angstrom from IUE low resolution spectra has also been compared with standard stars. The resulting spectral type is B3.5 V [ with a reddening of E(B - V) = 0.21 mag]. Using the magnitude differen ce between the two stars and the Cepheid luminosity, the binary compon ents are compared with evolutionary tracks computed by four groups. A mass between 5.5 and 6.0M. results from all tracks. On the other hand, the relatively small luminosity difference between the two stars is o nly consistent with tracks with minimal convective overshoot and a com panion nearing the end of the main sequence phase.