The Orientation of the Eta Carinae Binary System

Abstract

We examine a variety of observations that shed light on the orientation of the semi-major axis of the Eta Carinae massive binary system. Under several assumptions we study the following observations: The Doppler shifts of some He I P-Cygni lines that is attributed to the secondary's wind, of one Fe II line that is attributed to the primary's wind, and of the Paschen emission lines which are attributed to the shocked primary's wind, are computed in our model and compared with observations. We compute the hydrogen column density toward the binary system in our model, and find a good agreement with that deduced from X-ray observations. We calculate the ionization of surrounding gas blobs by the radiation of the hotter secondary star, and compare with observations of a highly excited [Ar III] narrow line. We find that all of these support 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, in its highly eccentric (e~0.9) orbit. Further supporting arguments are also listed, followed by discussion of some open and complicated issues.

12 pages, 9 figures

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• Constraining the Absolute Orientation of Eta Carinae's Binary Orbit: A 3-D Dynamical Model for the Broad [Fe III] Emission
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• He II 4686 in eta Carinae: collapse of the wind-wind collision region during periastron passage
• Detection of high-velocity material from the wind-wind collision zone of Eta Carinae across the 2009.0 periastron passage
• Eta Carinae's 2014.6 Spectroscopic Event: Clues to the Long-term Recovery from its Great Eruption
• Critical Differences and Clues in Eta Car's 2009 Event
• Hard X-ray identification of Eta Carinae and steadiness close to periastron
• Modelling the Central Constant Emission X-ray component of eta Carinae
• Near-Infrared Evidence for a Sudden Temperature Increase in Eta Carinae
• N II 5668-5712, a New Class of Spectral Features in Eta Carinae
• Prediction for the He I 10830A Absorption Wing in the Coming Event of Eta Carinae
• 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
• 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)