Eta Carinae: an evolving view of the central binary, its interacting winds and its foreground ejecta

TL;DR

Over two decades of HST observations reveal significant changes in Eta Carinae's UV spectra, showing increased ionization, wind interactions, and evolving circumstellar structures, enhancing understanding of its binary system and ejecta.

Contribution

This study provides the first long-term UV spectral monitoring of Eta Carinae, revealing evolving wind interactions and ionization states with detailed spectral analysis.

Findings

FUV flux increased nearly ten-fold over two decades.

Ionization of circumstellar shells has increased, destroying molecular hydrogen.

High velocity transient absorptions indicate wind acceleration and bowshock formation.

Abstract

FUV spectra of Eta Car, recorded across two decades with HST/STIS, document multiple changes in resonant lines caused by dissipating extinction in our line of sight. The FUV flux has increased nearly ten-fold which has led to increased ionization of the multiple shells within the Homunculus and photo-destruction of molecular hydrogen. Comparison of observed resonant line profiles with CMFGEN model profiles allows separation of wind-wind collision and shell absorptions from the primary wind, P Cygni profiles.The dissipating occulter preferentially obscured the central binary and interacting winds relative to the very extended primary wind. We are now able to monitor changes in the colliding winds with orbital phase. High velocity transient absorptions occurred across the most recent periastron passage, indicating acceleration of the primary wind by the secondary wind which leads to a downstream, high velocity bowshock that is newly generated every orbital period. There is no evidence of changes in the properties of the binary winds.