Imaging with HST the time evolution of Eta Carinae's colliding winds

TL;DR

This study uses HST/STIS observations to image and analyze the evolving wind-wind interaction region of Eta Carinae, revealing detailed 3D structures and orbital orientation, enhancing understanding of this massive binary system.

Contribution

First complete imaging of Eta Carinae's extended wind interaction region, providing new insights into its 3D orbital orientation and wind morphology.

Findings

Blue-shifted emission is symmetric and elongated NE-SW.

Red-shifted emission is asymmetric and extends N-NW.

Results support a specific 3D orbital orientation with inclination ~138°.

Abstract

We report new HST/STIS observations that map the high-ionization forbidden line emission in the inner arcsecond of Eta Car, the first that fully image the extended wind-wind interaction region of the massive colliding wind binary. These observations were obtained after the 2009.0 periastron at orbital phases 0.084, 0.163, and 0.323 of the 5.54-year spectroscopic cycle. We analyze the variations in brightness and morphology of the emission, and find that blue-shifted emission (-400 to -200 km s-1) is symmetric and elongated along the northeast-southwest axis, while the red-shifted emission (+100 to +200 km s-1) is asymmetric and extends to the north- northwest. Comparison to synthetic images generated from a 3-D dynamical model strengthens the 3-D orbital orientation found by Madura et al. (2011), with an inclination i \approx 138\degree, argument of periapsis {\omega} \approx 270\degree, and an orbital axis that is aligned at the same PA on the sky as the symmetry axis of the Homunculus, 312\degree. We discuss the potential that these and future mappings have for constraining the stellar parameters of the companion star and the long-term variability of the system.