The Orientation of the Eta Carinae Binary System

TL;DR

This study analyzes various observational data and models to determine the orientation of the Eta Carinae binary system, concluding that the secondary star is mostly behind the primary except near periastron.

Contribution

The paper provides a comprehensive model integrating multiple observations to constrain the orbital orientation of Eta Carinae, highlighting the secondary's position relative to the primary.

Findings

Secondary star is mostly behind the primary during most of the orbit.

Hydrogen column density matches X-ray observations.

Secondary star approaches the observer near periastron.

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.