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R. M. Humphreys, M. Koppelman (Univ. Minnesota)
The Harvard plate collection contains objective prism spectra of eta Car from 1892 to 1941. Our visual inspection combined with measurement of the digitized scans of many of the spectra shows no evidence of high excitation emission lines, in particular the He I line at 4471A during this time. The star was thus always in what is now called its "low excitation" state until about 1944 when Gaviola (1953) obtained spectra during 1944 - 1951 showing He I and other high excitation lines. These lines are now common in groundbased spectra except during the "spectroscopic events" when the high excitation lines weaken. Apparently there was no 5.5 year cycle and no "spectroscopic events" as we understand them today in eta Car's spectroscopic record prior to 1948 when the the first "low excitation" state was recorded. This spectroscopic transition from a common low excitation spectrum to a spectrum with high excitation lines corresponds to a time when the object brightened by more than a magnitude.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.