Program: GS-2009B-Q-6

As the best-observable example of an evolved very massive star, $\eta$ Carinae has a remarkable history of revealing faults in existing theory. A 5.5-year cycle of spectroscopic events has lately become useful in this regard. Meanwhile, $\eta$ Car's structure can also be studied via its unsteady recovery from the giant ``SN Impostor'' eruption observed in the 1840s. {\it There is strong evidence that this recovery process entered a more rapid stage 10--15 years ago.\/} The 2003.5 spectroscopic event clearly differed from that seen in 1998.0, but the earlier example was not observed in great detail. Thus it is extremely important to observe the event predicted for 2009.0, in order to assess how it differs from the well-observed 2003.5 event. This is arguably one of the most incisive observational tasks that can be done in the near future regarding structure and instabilities of the most massive stars. {\bf This proposal completes a program that has been approved through January 2009. Long-term status for last semester's proposal was recommended by the NOAO TAC, but then was denied by the international TAC.}