Numerical simulations of wind-equatorial gas interaction in eta Carinae

TL;DR

This paper uses 3D gas-dynamical simulations to explain the asymmetric outflow morphology of eta Carinae by modeling the collision of the primary stellar wind with dense equatorial gas, reproducing key velocity map features.

Contribution

It introduces a simplified model of the dense equatorial ejecta as spherical clouds to qualitatively reproduce observed velocity maps of eta Carinae's outflows.

Findings

Qualitative match of velocity maps achieved

Dense clouds closer to observer than the binary system

Fast secondary wind has negligible role in the model

Abstract

We perform three-dimensional gas-dynamical simulations and show that the asymmetric morphology of the blue and red-shifted components of the outflow at hundreds of astronomical units (AU) from the massive binary system eta Carinae can be accounted for from the collision of the free primary stellar wind with the slowly expanding dense equatorial gas. Owing to the very complicated structure of the century-old equatorial ejecta, that is not fully spatially resolved by observations, we limit ourselves to modelling the equatorial dense gas by one or two dense spherical clouds. Because of that we reproduce the general qualitative properties of the velocity maps, but not the fine details. The fine details of the velocity maps can be matched by simply structuring the dense ejecta in an appropriate way. The blue and red-shifted components are formed in the post-shock flow of the primary wind, on the two sides of the equatorial plane, respectively. The fast wind from the secondary star plays no role in our model, as for most of the orbital period in our model the primary star is closer to us. The dense clouds are observed to be closer to us than the binary system is, and so in our model the primary star faces the dense equatorial ejecta for the majority of the orbital period.