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

TL;DR

This study uses high-resolution HST/STIS spectrograms to analyze the ionization structure of Eta Carinae's Weigelt knots, revealing unexpected ionization zones that challenge simple models and suggesting new directions for understanding their nature.

Contribution

The paper provides the first partial resolution of ionization zones in the Weigelt knots with high spatial accuracy, revealing unexpected ionization patterns contrary to simple models.

Findings

Higher ionization occurs on the outer side of the knots, farther from Eta Carinae.

Spectrograms offer more reliable spatial measurements than images.

The technique can be applied to study the knots' proper motion.

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.