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Paper: The Bipolar Wind of Eta Carinae
Volume: 332, The Fate of the Most Massive Stars
Page: 143
Authors: Smith, N.
Abstract: Here I briefly review the main points of η Car's stellar wind geometry as deduced from multiple viewing directions seen in HST/STIS spectra of the Homunculus reflection nebula. H and He I line profiles are latitude dependent, and point toward a bipolar wind geometry with higher velocity, density, and mass flux at the poles, and with higher ionization and more UV flux escaping from lower-latitude zones of the wind. This wind geometry is true regardless of its origin: it may be caused by either a line driven wind from a rotating star with equatorial gravity darkening, or the wind structure may be induced by ionization and wind-wind interactions from a hot companion star orbiting in the equatorial plane (both are likely to be influential). During a spectroscopic event, the polar region of the wind does not change much, whereas the lower density/higher ionzation region of the wind closer to the equator appears to fill-in, making the wind appear quasi-spherical for a short time. These changes in the wind resemble a shell ejection, but are probably induced by a companion star in some way, and play a critical role in η Car's 5.5 yr cycle.
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