Inverted Ionization Zones in Eta Carinae's "Weigelt Knots"

Abstract

The Weigelt knots, dense slow-moving ejecta near eta Car, are mysterious in structure as well as in origin. Using a special set of spectrograms obtained with the HST/STIS, we have partially resolved the ionization zones of one knot to an accuracy of about 10 mas. Contrary to simple models, higher ionization levels occur on the_outer_ side of the knot, i.e., farther from the star. They cannot represent a bow shock, and no truly satisfying explanation is yet available -- though we sketch one tentative possibility. We emphasize that STIS spectrograms provide far more reliable spatial measurements of the Weigelt Knots than HST images do, and this technique can also be applied to the knots' proper motion problem.

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