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The magnetic field of β Cep and the Be phenomenon

Published online by Cambridge University Press:  12 April 2016

H.F. Henrichs ,
J.A. de Jong ,
J.-F. Donati ,
C. Catala ,
G.A. Wade ,
S.L.S. Shorlin ,
P.M. Veen ,
J.S. Nichols  and
L. Kaper
H.F. Henrichs
Affiliation:
Astronomical Institute, University of Amsterdam, Kruislaan 403, 1098SJ Amsterdam, Netherlands
J.A. de Jong
Affiliation:
Astronomical Institute, University of Amsterdam, Kruislaan 403, 1098SJ Amsterdam, Netherlands
J.-F. Donati
Affiliation:
Observatoire Midi-Pyrénées, Toulouse, France
C. Catala
Affiliation:
Observatoire Midi-Pyrénées, Toulouse, France
G.A. Wade
Affiliation:
Dept. of Astronomy, Univ. of Toronto at Mississauga, Ontario, Canada
S.L.S. Shorlin
Affiliation:
Physics and Astronomy Dept., Univ. of Western Ontario, Canada
P.M. Veen
Affiliation:
Sterrewacht Leiden, Leiden University, Netherlands
J.S. Nichols
Affiliation:
Harvard/Smithsonian Center for Astrophysics, Cambridge, U.S.A
L. Kaper
Affiliation:
Astronomical Institute, University of Amsterdam

Abstract

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New circular spectropolarimetric observations of the B1 IIIe star β Cep (υsini = 25 km s−1) show a sinusoidally varying weak longitudinal magnetic field (~ 200 G peak-to-peak). The period corresponds to the 12 day period in the stellar wind variations observed in ultraviolet spectral lines. Maximum field occurs at maximum emission in the UV wind lines. This gives compelling evidence for a magnetic-rotator model for this star, with an unambiguous rotation period of 12 days.

The similarity between the Hα emission phases in β Cep and in Be stars suggests that the origin of the Be phenomenon does not have to be rapid rotation: we propose that in β Cep the velocity to bring material in (Keplerian) orbit is provided by the high corotation velocity at the Alfvén radius (~10 R*), whereas in Be stars this is done by the rapid rotation of the surface. In both cases the cause of the emission phases has still to be found. Weak temporary magnetic fields remain the strongest candidate.

A full paper, with results including additional measurements in June and July 1999, will appear in A & A.

Type
4. Aperiodic Variations
Information
International Astronomical Union Colloquium , Volume 175: The Be Phenomenon in Early-Type Stars , 2000 , pp. 324 - 329
Copyright
Copyright © Astronomical Society of the Pacific 2000

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