Eta Carinae across the 2003.5 Minimum: Deciphering the Spectrum toward Weigelt D

Abstract

Hubble Space Telescope Space Telescope Imaging Spectrograph (HST STIS) near-ultraviolet (NUV) echelle spectra reveal complex structure in the sight line toward the Weigelt D condensation located 0.25" north-northwest of η Car. In previous studies, the Weigelt condensations have been described to exhibit pure emission line spectra dominated by transitions in mainly singly and doubly ionized iron-group elements. However, high spectral (R~100,000) and angular (<0.060" FWHM) resolutions show that the spectra are modified by circumstellar (CS) absorption and stellar wind lines formed as far as 1500 AU from the central source. This analysis uses data recorded between 2000 October and 2004 March to monitor changes in emission and absorption as the UV photoexciting fluxes from η Car drop and later reappear. We compare changes in the wind profiles seen against the star and the CS absorptions to gain knowledge of the properties of the extended wind and the ejecta. Complete spectra, in the wavelength region 2424-2706 Å, with line identifications are available in the electronic edition of this paper.