The Interaction of the Eta Carinae Primary Wind with a Century Old Slow Equatorial Ejecta

TL;DR

This paper models the asymmetric blue and red shifted outflow components near Eta Carinae as resulting from the collision of the primary stellar wind with dense, slowly expanding equatorial gas, explaining observed line emissions and morphology.

Contribution

The study introduces a model where the primary wind's collision with the equatorial ejecta explains the outflow asymmetries without involving the secondary wind.

Findings

The blue and red shifted components correlate with the dense equatorial gas distribution.

Postshock flow of the primary wind accounts for observed line intensities.

The model explains asymmetries due to line-of-sight inclination.

Abstract

We argue that the asymmetric morphology of the blue and red shifted components of the outflow at hundreds of AU from the massive binary system Eta Carinae can be understood from the collision of the primary stellar wind with the slowly expanding dense equatorial gas. Recent high spatial observations of some forbidden lines, e.g. [Fe III] lambda4659, reveal the outflowing gas within about one arcsecond (2300 AU) from Eta Car. The distribution of the blue and red shifted components are not symmetric about the center, and they are quite different from each other. The morphologies of the blue and red shifted components correlate with the location of dense slowly moving equatorial gas (termed the Weigelt blob environment; WBE), that is thought to have been ejected during the 1887 - 1895 Lesser Eruption. In our model the division to the blue and red shifted components is caused by the postshock flow of the primary wind on the two sides of the equatorial plane after it collides with the WBE. The fast wind from the secondary star plays no role in our model for these components, and it is the freely expanding primary wind that collides with the WBE. Because the line of sight is inclined to the binary axis, the two components are not symmetric. We show that the postshock gas can also account for the observed intensity in the [Fe III] lambda4659 line.