The variable 6307A emission line in the spectrum of Eta Carinae: blueshifted [S III] 6313A from the interacting winds

TL;DR

This study identifies a blueshifted [S III] emission line in Eta Carinae's spectrum, revealing detailed spatial and velocity structures of the interacting stellar winds through high-resolution observations.

Contribution

The paper provides the first identification of the blueshifted [S III] 6313A line in Eta Carinae, offering new insights into the wind interaction regions via spatially and velocity-resolved forbidden line imaging.

Findings

Forbidden lines show spatially and velocity-resolved structures.

Highly ionized forbidden emissions are systematically blueshifted.

Density estimates range from 10^6 to 10^10 cm^-3 with temperatures 8,000-13,000K.

Abstract

The 6307A emission line in the spectrum of Eta Car (Martin et al. 2006) is blue-shifted [S III] 6313A emission originating from the outer wind structures of the massive binary system. We realized the identification while analyzing multiple forbidden emission lines not normally seen in the spectra of massive stars. The high spatial and moderate spectral resolutions of HST/STIS resolve forbidden lines of Fe+, N+, Fe++, S++, Ne++ and Ar++ into spatially and velocity-resolved rope-like features originating from collisionally-excited ions photo-ionized by UV photons or collisions. While the [Fe II] emission extends across a velocity range of +/-500 km/s out to 0."7, more highly ionized forbidden emissions are systematically blue-shifted (-500 to +200 km/s) and extend only to 0."4. The [Fe II] defines the outer regions of the massive primary wind. The [N II], [Fe III] emission define the the outer wind interaction regions directly photo-ionized by far-UV radiation. Variations in emission of [S III] 9533A, 9071A and 6313A suggest density ranges of 10^6 to 10^10 cm^-3 for electron temperatures ranging from 8,000 to 13,000K. Mapping the temporal changes of the emission structure at critical phases of the 5.54-year period will provide important diagnostics of the interacting winds.