Program: GS-2006A-Q-35

Every 5.5 years, $\eta$ Carinae experiences a dramatic ``spectroscopic event'' when high-excitation lines in its UV, optical, and IR spectrum disappear, and its hard X-ray and radio continuum flux crash. This periodicity has been attributed to a very eccentric binary system with a shell ejection occurring at periastron. Mid-IR images and spectra with T-ReCS are needed to measure changes in the current bolometric luminosity and to trace dust formation episodes. This will provide a direct estimate of the mass ejected. Near-IR emission lines trace related changes in the post-event wind and ionization changes in the circumstellar environment needed to test specific models for the cause of $\eta$ Car's variability as it recovers from its recent ``event''. High resolution near-IR spectra with GNIRS will continue the important work of HST/STIS, investigating changes in the direct and reflected spectrum of the stellar wind, and ionization changes in the nebula. The complex kinematic structure of $\eta$ Car's ejecta also holds important clues to its mass ejection history, and is essential for interpreting other data. Phoenix can provide a unique kinematic map of the complex density and time-variable ionization structure of $\eta$ Car's nebula, which is our best example of the pre-explosion environment of very massive stars.