VLT UVES Observations of the Balmer Line Variations of η Carinae during the 2003 Spectroscopic Event

Abstract

We present high spectral resolution echelle observations of the Balmer line variations during the 2003.5 "spectroscopic event" of η Carinae. Spectra have been recorded of both η Car and the Homunculus at the "FOS4" position in its southeast lobe. This spot shows a reflected stellar spectrum that is less contaminated by nebular emission lines than ground-based observations of the central object itself. Our observations show that the spectroscopic event is much less pronounced at this position than when seen directly on η Car using the Hubble Space Telescope Space Telescope Imaging Spectrograph. Assuming that the reflected spectrum is indeed latitude-dependent, this indicates that the spectral changes during the event seen pole-on (FOS4) are different from those closer to the equator (directly on the star). In contrast to the spectrum of the star, the scattered spectrum of FOS4 always shows pronounced P Cygni absorption with little variation across the spectroscopic event. After that event an additional high-velocity absorption component appears. The emission profile is more peaked at FOS4 and consists of at least three distinct components, of which the reddest one shows the strongest changes through the event. The data seem to be compatible with changes in latitudinal wind structure of a single star, with or without the help of a secondary star, or the onset of a shell ejection during the spectroscopic event.