Detection of a Hot Binary Companion of (eta)Carinae

We report the detection of a hot companion of (eta) Carinae using high-resolution spectra (905-1180 (angstrom)) obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite. Observations were A obtained at two epochs of the 2024 day orbit: 2003 June, during ingress to the 2003.5 X-ray eclipse, and 2004 April, several months after egress. These data show that essentially all the far-UV flux from (eta) Car shortward of Ly(alpha) disappeared at least 2 days before the start of the X-ray eclipse (2003 June 29), implying that the hot companion, (alpha) Car B, was also eclipsed by the dense wind or extended atmosphere of (eta) Car A. Analysis of the far-UV spectrum shows that (eta) Car B is a luminous, hot star. The N II (lambda)(lambda) 1084-1086 emission feature suggests that it may be nitrogen-rich. The observed far-UV flux levels and spectral features, combined with the timing of their disappearance, is consistent with (eta) Car being a massive binary system.