On the multiplicity of eta Carinae

The nebula around the luminous blue variable (LBV) eta Car is extremely N r ich and C and O poor, which is indicative of CNO-cycle products. On the oth er hand, the recent Hubble Space Telescope-Goddard High-Resolution Spectrog raph observation of the nucleus of eta Car shows the spectrum of a star wit h stellar-wind lines of C II, C IV, Si II, Si IV, etc. The spectrum is very similar to those of the LBV star P Cygni and of WN9/Ofpe stars. This line spectrum is indicative of a photosphere that is only mildly enhanced by CN- cycle products. This situation of a nebula that is chemically more advanced than the central star cannot be reached by the evolution of a single star. The dichotomy shows that the star whose spectrum now dominates the nucleus was not the star that ejected the nebula. We discuss this evidence for mul tiplicity and combine it with the information about the 5.5 yr periodicity in the emission lines.