Accretion of Dense Clumps in the Periastron Passage of Eta Carinae

TL;DR

This paper uses 3D hydrodynamical simulations to show how dense clumps in Eta Carinae's primary wind trigger accretion onto the secondary star near periastron, explaining observed X-ray minima.

Contribution

It demonstrates the role of wind clumps and instabilities in initiating accretion in Eta Carinae, providing a detailed physical mechanism for observed phenomena.

Findings

Dense wind clumps trigger accretion near periastron.

Accretion begins about a week before periastron.

Clump formation by instabilities explains the X-ray minimum.

Abstract

We perform 3D hydrodynamical numerical simulations of the winds interaction process in the massive binary system $\eta$ Carinae, and find the secondary star to accrete mass from the dense primary wind close to periastron passage. This accretion is thought to result in the spectroscopic event and X-ray minimum observed in the system every revolution. In this study we limit ourselves to explore the role of clumps in the primary wind in triggering the accretion process. We include the gravity of the secondary star and the orbital motion starting 19 days (90 degrees) before periastron passage. The accretion process is triggered by dense clumps that cannot be decelerated by the ram pressure of the secondary wind. The dense clumps are formed by instabilities in the thin dense shell formed by the shocked primary wind gas. We explore the role of the numerical viscosity and some physical parameters on the initiation of the accretion process, and explain the unique properties of $\eta$ Car that allow for the periastron accretion process to occur. The accretion starts about a week before periastron passage, as is required to explain the several weeks long X-ray minimum.