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The dichotomy between strong and ultra-weak magnetic fields among intermediate-mass stars

Published online by Cambridge University Press:  07 August 2014

François Lignières
Affiliation:
CNRS, Institut de Recherche en Astrophysique et Planétologie 14 avenue Edouard Belin, 31400 Toulouse, France email: francois.lignieres@irap.omp.eu Université de Toulouse, UPS-OMP, IRAP 31400 Toulouse, France
Pascal Petit
Affiliation:
CNRS, Institut de Recherche en Astrophysique et Planétologie 14 avenue Edouard Belin, 31400 Toulouse, France email: francois.lignieres@irap.omp.eu Université de Toulouse, UPS-OMP, IRAP 31400 Toulouse, France
Michel Aurière
Affiliation:
CNRS, Institut de Recherche en Astrophysique et Planétologie 14 avenue Edouard Belin, 31400 Toulouse, France email: francois.lignieres@irap.omp.eu Université de Toulouse, UPS-OMP, IRAP 31400 Toulouse, France
Gregg A. Wade
Affiliation:
Department of Physics, Royal Military College of CanadaPO Box 17000, Station Forces, Kingston, Ontario K7K 7B4, Canada
Torsten Böhm
Affiliation:
CNRS, Institut de Recherche en Astrophysique et Planétologie 14 avenue Edouard Belin, 31400 Toulouse, France email: francois.lignieres@irap.omp.eu Université de Toulouse, UPS-OMP, IRAP 31400 Toulouse, France
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Abstract

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Until recently, the detection of magnetic fields at the surface of intermediate-mass main-sequence stars has been limited to Ap/Bp stars, a class of chemically peculiar stars. This class represents no more than 5-10% of the stars in this mass range. This small fraction is not explained by the fossil field paradigm that describes the Ap/Bp type magnetism as a remnant of an early phase of the star-life. Also, the limitation of the field measurements to a small and special group of stars is obviously a problem to study the effect of the magnetic fields on the stellar evolution of a typical intermediate-mass star.

Thanks to the improved sensitivity of a new generation of spectropolarimeters, a lower bound to the magnetic fields of Ap/Bp stars, a two orders of magnitude desert in the longitudinal magnetic field and a new type of sub-gauss magnetism first discovered on Vega have been identified. These advances provide new clues to understand the origin of intermediate-mass magnetism as well as its influence on stellar evolution. In particular, a scenario has been proposed whereby the magnetic dichotomy between Ap/Bp and Vega-like magnetism originate from the bifurcation between stable and unstable large scale magnetic configurations in differentially rotating stars. In this paper, we review these recent observational findings and discuss this scenario.

Type
Contributed Papers
Copyright
Copyright © International Astronomical Union 2014 

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