EDP Sciences
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Volume 435, Number 1, May III 2005
Page(s) 303 - 312
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20042547

A&A 435, 303-312 (2005)
DOI: 10.1051/0004-6361:20042547

A spectroscopic event of $\eta$ Car viewed from different directions: The data and first results

O. Stahl1, K. Weis2, D. J. Bomans2, K. Davidson3, T. R. Gull4 and R. M. Humphreys3

1  Landessternwarte Königstuhl, 69117 Heidelberg, Germany
    e-mail: O.Stahl@lsw.uni-heidelberg.de
2  Astronomisches Institut, Ruhr-Universität Bochum, Universitätsstr. 150, 44780 Bochum, Germany
3  Laboratory for Astronomy and Space Science, NASA-Goddard Space Flight Center, Code 681, Greenbelt, MD 20771, USA
4  Astronomy Department, University of Minnesota, Minneapolis, MN 55455, USA

(Received 15 December 2004 / Accepted 28 January 2005 )

We present spectroscopic observations with high spectral resolution of $\eta$ Car as seen by the SE lobe of the Homunculus nebula over the 2003.5 "spectroscopic event". The observed spectra represent the stellar spectrum emitted near the pole of the star and are much less contaminated with nebular emission lines than direct observations of the central object. The "event" is qualitatively similar near the pole to what is observed in direct spectra of the star (more equator-on at 45°), but shows interesting differences. The observations show that the equivalent width changes of H$\alpha$ emission and other lines are less pronounced at the pole than in the line of sight. Also the absorption components appear less variable. A pronounced high-velocity absorption is present near the event in the He I lines indicating a mass-ejection event. This feature is also seen, but less pronounced, in the hydrogen lines. He II$\lambda$4686 emission is observed for a brief period of time near the event and appears, if corrected for light travel time, to precede similar emission in the direct view. Our observations indicate that the event is probably not only a change in ionization and excitation structure or a simple eclipse-like event.

Key words: stars: individual: $\eta$ Car -- stars: circumstellar matter -- stars: mass-loss -- stars: evolution

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© ESO 2005