η Carinae: Testing a binary orbit model with the Hubble Space Telescopei/Space Telescope Imaging Spectrograph

Ground-based spectroscopy of η Car shows periodic changes in some emission-line wavelengths. These variations have been cited as strong evidence that this object is a 5.5 yr binary system and have been used to produce specific orbit models. High spatial resolution data obtained with the Hubble Space Telescope/Space Telescope Imaging Spectrograph, however, do not confirm the predicted velocity behavior; therefore, the published orbit models are almost certainly invalid. Wavelength fluctuations seen at ground-based spatial resolution most likely result from other effects, which we describe. If this object is a binary system (which has not been proven), then the parameters of the secondary star and of the orbit remain largely unknown.