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The Stellar Wind Geometry of η Carinae

Published online by Cambridge University Press:  12 April 2016

Nathan Smith ,
Kris Davidson ,
Theodore R. Gull  and
Kazunori Ishibashi
Nathan Smith
Affiliation:
Astronomy Department, University of Minnesota, 116 Church St. SE, Minneapolis, MN 55455
Kris Davidson
Affiliation:
Astronomy Department, University of Minnesota, 116 Church St. SE, Minneapolis, MN 55455
Theodore R. Gull
Affiliation:
NASA/Goddard Space Flight Center, Code 681, Greenbelt, MD 20771
Kazunori Ishibashi
Affiliation:
Center for Space Research, MIT, Massachusetts Avenue NE90-6011, Cambridge, MA 02139

Abstract

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The Homunculus reflection nebula around η Carinae provides a rare opportunity to observe a star from more than one direction. For η Car, the nebula’s geometry is known well enough to infer how wind profiles vary with latitude. STIS spectra of the Homunculus show directly that η Car has an aspherical stellar wind. P Cygni absorption in Balmer lines depends on latitude, with relatively high velocities and strong absorption near the polar axis. Stronger absorption at high latitudes is surprising, and it suggests higher mass flux toward the poles, perhaps resulting from equatorial gravity darkening on a rotating star. Reflected profiles of He I lines are more puzzling, and offer clues to η Car’s circumstellar structure. The bipolar wind geometry may imply that intrinsically asymmetric ejection helped form the Homunculus. It is also critical for understanding this star’s variability and evolution.

Type
Research Article
Information
International Astronomical Union Colloquium , Volume 187: Exotic Stars as Challenges to Evolution , 2002 , pp. 107 - 113
Copyright
Copyright © Astronomical Society of the Pacific 2002

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