Using X-Ray Observations to Explore the Binary Interaction in Eta Carinae

Abstract

We study the usage of the X-ray light curve, column density toward the hard X-ray source, and emission measure (density square times volume), of the massive binary system Eta Carinae to determine the orientation of its semi-major axis. The source of the hard X-ray emission is the shocked secondary wind. We argue that, by itself, the observed X-ray flux cannot teach us much about the orientation of the semi-major axis. Minor adjustment of some unknown parameters of the binary system allows to fit the X-ray light curve with almost any inclination angle and orientation. The column density and X-ray emission measure, on the other hand, impose strong constrains on the orientation. We improve our previous calculations and show that the column density is more compatible with an orientation where for most of the time the secondary - the hotter, less massive star - is behind the primary star. The secondary comes closer to the observer only for a short time near periastron passage. The ten-week X-ray deep minimum, which results from a large decrease in the emission measure, implies that the regular secondary wind is substantially suppressed during that period. This suppression is most likely resulted by accretion of mass from the dense wind of the primary luminous blue variable (LBV) star. The accretion from the equatorial plane might lead to the formation of a polar outflow. We suggest that the polar outflow contributes to the soft X-ray emission during the X-ray minimum; the other source is the shocked secondary wind in the tail. The conclusion that accretion occurs at each periastron passage, every five and a half years, implies that accretion had occurred at a much higher rate during the 20 Great Eruption of Eta Carinae in the 19th century.

MNRAS, in press. 21 pages, 5 figures

References in corpus (11)

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• Critical Differences and Clues in Eta Car's 2009 Event
• Imaging with HST the time evolution of Eta Carinae's colliding winds
• A Lighthouse Effect in Eta Carinae
• Orbital Parameters for the $250M_{\odot }$ Eta Carinae Binary System
• Accretion at the periastron passage of Eta Carinae
• Simulating the Response of the Secondary Star of Eta Carinae to Mass Accretion at Periastron Passage
• Fast Ejecta Resulted from Jet-Wind Interaction in the Great Eruption of Eta Carinae
• Wind Collision and Accretion Simulations of the Massive Binary System HD 166734
• The X-ray properties of Eta Carinae during its 2020 X-ray minimum
• The Interaction of the Eta Carinae Primary Wind with a Century Old Slow Equatorial Ejecta
• Explaining the transient fast blue absorption lines in the massive binary system Eta Carinae
• Accretion in the Binary System GG Carinae and Implications for B[e] Supergiants
• Numerical simulations of wind-equatorial gas interaction in eta Carinae
• The orientation of Eta Carinae and the powering mechanism of intermediate luminosity optical transients (ILOTs)