Multi-Wavelength Implications of the Companion Star in Eta Carinae

TL;DR

This study uses 3-D simulations and radiative transfer to analyze how the companion star in Eta Carinae influences its observable spectra and photometry across multiple wavelengths, revealing the significance of the Bore Hole effect.

Contribution

It introduces detailed 3-D models of Eta Carinae's colliding winds that clarify the companion star's impact on observed spectra and photometry, especially through the Bore Hole effect.

Findings

The companion star significantly affects UV spectra and H-alpha profiles.

The Bore Hole effect enhances radiation escape from the primary wind.

Models match observed spectral and photometric features.

Abstract

Eta Carinae is considered to be a massive colliding wind binary system with a highly eccentric (e \sim 0.9), 5.54-yr orbit. However, the companion star continues to evade direct detection as the primary dwarfs its emission at most wavelengths. Using three-dimensional (3-D) SPH simulations of Eta Car's colliding winds and radiative transfer codes, we are able to compute synthetic observables across multiple wavebands for comparison to the observations. The models show that the presence of a companion star has a profound influence on the observed HST/STIS UV spectrum and H-alpha line profiles, as well as the ground-based photometric monitoring. Here, we focus on the Bore Hole effect, wherein the fast wind from the hot secondary star carves a cavity in the dense primary wind, allowing increased escape of radiation from the hotter/deeper layers of the primary's extended wind photosphere. The results have important implications for interpretations of Eta Car's observables at multiple wavelengths.