Properties of the -513 km/s Ejecta in the Spectrum of Eta Carinae

Abstract:
In the spectral region 2400-3160A of Eta Carinae, we have identifiedapproximately 500 absorption lines each with up to twenty velocitycomponents.The -512 km/s component is truely unique as 1) the typicalline width is <3 km/s, 2) the identified lines are in Fe I, Fe II, VII and Ti II, and 3) the lines originate from lower levels up to 2000cm-1 above the ground level. We have measured the velocity centers, fullwidth at half maximum and equivalent widths for approximately 100absorption lines. Initial results were very confusing as we found morevariation in central velocities than would be expected from known STISechelle wavelength standards. Upon further review, we found that thereporteded wavelengths in the NIST and Kurucz databases were notsufficiently accurate. S. Johansson searched FTS laboratory measurementsperformed at Lund for V II and Ti II and provided much improvedwavelength measures. Likewise, we find more variation in column densitythan expected statistically from the accuracy of the equivalent widthsfor lines originating from the same energy level. We are reviewing thepublished gf values and our measurements to improve the measured columndensities. Some spectroscopy of the ejecta has already been accomplishedat two different epochs. Preliminary measures of equivalent widthsindicate there may be some variation with time, but we awaitmeasurements planned for July 2003 during the upcoming spectroscopicminimum of Eta Carinae. These observations were accomplished throughSTScI and funding was from STIS GTO resources.