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Broadband Linear Polarization in Ap Stars

Published online by Cambridge University Press:  12 April 2016

Marco Landolfi ,
Egidio Landi Degl’Innocenti ,
Maurizio Landi Degl’Innocenti ,
Jean-Louis Leroy  and
Stefano Bagnulo
Marco Landolfi
Affiliation:
Osservatorio Astrofisico di Arcetri
Egidio Landi Degl’Innocenti
Affiliation:
Dipartimento di Astronomia e Scienza dello Spazio, Università di Firenze
Maurizio Landi Degl’Innocenti
Affiliation:
Gruppo Nazionale di Astronomia, Unità di Ricerca di Arcetri
Jean-Louis Leroy
Affiliation:
Observatoire Midi-Pyrénées
Stefano Bagnulo
Affiliation:
Università di Firenze

Abstract

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Broadband linear polarization in the spectra of Ap stars is believed to be due to differential saturation between σ and π Zeeman components in spectral lines. This mechanism has been known for a long time to be the main agent of a similar phenomenon observed in sunspots. Since this phenomenon has been carefully calibrated in the solar case, it can be confidently used to deduce the magnetic field of Ap stars.

Given the magnetic configuration of a rotating star, it is possible to deduce the broadband polarization at any phase. Calculations performed for the oblique dipole model show that the resulting polarization diagrams are very sensitive to the values of i (the angle between the rotation axis and the line of sight) and β (the angle between the rotation and magnetic axes). The dependence on i and β is such that the four-fold ambiguity typical of the circular polarization observations ((i,β), (β,i), (π-i,π-β), (π-β,π-i)) can be removed.

Type
II. Magnetic Fields: Observations and Theories
Information
International Astronomical Union Colloquium , Volume 138: Peculiar versus Normal Phenomena in A-Type and Related Stars , 1993 , pp. 305 - 309
Copyright
Copyright © Astronomical Society of the Pacific 1993

References

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