The orbital kinematics of eta Carinae over three periastra with a possible detection of the elusive secondary's motion

TL;DR

This study analyzes eta Carinae's orbital motion over three periastra using spectroscopic data, revealing potential evidence of the secondary star's motion and suggesting the first detection of its emission.

Contribution

It provides improved measurements of eta Carinae's orbital kinematics and reports possible detection of the elusive secondary star's emission line.

Findings

Radial velocity measurements of the primary star's H-beta line.

Possible detection of the secondary's He II emission line.

Evidence supporting a Wolf-Rayet companion.

Abstract

The binary eta Carinae is the closest example of a very massive star, which may have formed through a merger during its Great Eruption in the mid-nineteenth century. We aimed to confirm and improve the kinematics using a spectroscopic data set taken with the CTIO 1.5 m telescope over the time period of 2008-2020, covering three periastron passages of the highly eccentric orbit. We measure line variability of H-alpha and H-beta, where the radial velocity and orbital kinematics of the primary star were measured from the H-beta emission line using a bisector method. At phases away from periastron, we observed the He II 4686 emission moving opposite the primary star, consistent with a possible Wolf-Rayet companion, although with a seemingly narrow emission line. This could represent the first detection of emission from the companion.