Detection of the Ultraviolet Spectrum of the Hot Subdwarf Companion of 60 Cygni (B1 Ve) from a Survey of IUE Spectra of Be Stars

Abstract

Abstract We used archival International Ultraviolet Explorer (IUE) high-dispersion, short wavelength spectra data to search for evidence of the spectra of hot subdwarf companions of six rapidly rotating Be stars in binary systems. We searched for the signature of a hot companion through an analysis of the cross-correlation functions (CCFs) of observed and model spectra that were separated into primary and secondary components using a Doppler tomography algorithm and adopted spectroscopic orbital solutions. A positive detection of the flux from a hot companion was made for the reconstructed secondary CCF of just one target, 60 Cygni (B1 Ve). We estimate that the companion of the Be star in 60 Cygni has kK, mass ratio , and monochromatic flux ratio in the spectral region near 1525 Å. If the companions of the other target Be stars are also hot, then they must be faint and contribute less than of the UV flux (<0.6% in the case of γ Cas). We also discuss a shell episode of Pleione (28 Tau) recorded in the IUE spectran in an appendix.