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Ionization in the Winds of Early-B Stars: Constraints Imposed by EUVE

Published online by Cambridge University Press:  12 April 2016

J.J. MacFarlane ,
D.H. Cohen ,
J.P. Cassinelli  and
P. Wang
J.J. MacFarlane
Affiliation:
Department of Astronomy, University of Wisconsin, 475 N. Charter St., Madison, WI 53706, USA Fusion Technology Institute, University of Wisconsin, 1500 Johnson Drive, Madison, WI 53706, USA
D.H. Cohen
Affiliation:
Department of Astronomy, University of Wisconsin, 475 N. Charter St., Madison, WI 53706, USA
J.P. Cassinelli
Affiliation:
Department of Astronomy, University of Wisconsin, 475 N. Charter St., Madison, WI 53706, USA
P. Wang
Affiliation:
Fusion Technology Institute, University of Wisconsin, 1500 Johnson Drive, Madison, WI 53706, USA

Abstract

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Extreme Ultraviolet Explorer (EUVE) spectral observations of ε CMa (B2 II) provide significant new information about the ionization dynamics of its wind, its mass loss rate, and the interaction of its wind with the soft X-ray/EUV radiation field. We present results from wind ionization calculations which show how EUV radiation, emitted predominantly in the form of Fe IX-XVI lines from plasma with T ~ 1 – 3 × 106 K, significantly alters the ionization state of its wind. EUV photons from the hot plasma photoionize He II in the cool portion of ε CMa’s wind, producing anomalously high abundances of He III. The subsequent recombination from He III results in He II Lα (304 Å) and Lβ (256 Å) lines which are observed by EUVE. Also observed is O III λλ 374, which results from the O III λλ 304 multiplet being pumped by He II Lα — the Bowen mechanism (Cassinelli et al. 1995). We report on initial results from numerical simulations which show the effect of the Bowen mechanism on the O III 374 Å line emission.

Type
VII. Photospheres and Winds of Early-Type Stars
Information
International Astronomical Union Colloquium , Volume 152: Astrophysics in the Extreme Ultraviolet , 1996 , pp. 375 - 379
Copyright
Copyright © Kluwer 1996

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