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Astron. Astrophys. 358, 929-942 (2000)
Modelling of magnetic fields of CP stars
III. The combined interpretation of five different magnetic
observables: theory, and application to
![[FORMULA]](img1.gif)
Coronae Borealis
S. Bagnulo 1,
M. Landolfi 2,
G. Mathys 3 and
M. Landi Degl'Innocenti 4
1 Universität Wien, Institut für Astronomie, Türkenschanzstrasse 17, 1180 Wien, Austria (bagnulo@astro.univie.ac.at)
2 Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy (landolfi@arcetri.astro.it)
3 European Southern Observatory, Casilla 19001, Santiago 19, Chile (gmathys@eso.org)
4 C.N.R., Gruppo Nazionale di Astronomia, Unità di Ricerca di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy (mlandi@arcetri.astro.it)
Received 6 October 1999 / Accepted 2 February 2000
Abstract
The most common techniques for detecting magnetic fields of
chemically peculiar (CP) stars are based on the determination of some
quantities related to the magnetic morphology, which are obtained
through the analysis of Stokes I and V profiles, and on
observations of frequency integrated Stokes Q and U. In
previous papers of this series we set up a formalism aimed at
describing the magnetic field of CP stars in terms of a superposition
of a dipole and a quadrupole field, and we proposed a method to
recover the magnetic morphology from the combined analysis of those
observable quantities which can simply be expressed by means of
analytical formulas, namely: the mean longitudinal field, the
crossover, and the mean square field. Here we extend this method in
order to include those quantities for which numerical integrations are
required, i.e., the mean field modulus and the broadband linear
polarisation. Estimates of stellar radius and projected equatorial
velocity are also explicitly taken into account. We present an
application to the well-known CP star
![[FORMULA]](img2.gif)
CrB, the only star for which all
kinds of magnetic data are available. We find that
CrB, like most CP stars,
exhibits a complex magnetic structure, which may not be fully
accounted for even by a second-order multipolar expansion. However, we
are able to suggest two models which are compatible with all the
magnetic data.
Key words: stars: magnetic
fields 
polarization
stars: chemically
peculiar
stars: individual: fi CrB
Send offprint requests to: S. Bagnulo
Contents
- 1. Introduction
- 2. Expressions of the broadband linear polarisation and of the mean field modulus for the dipole plus quadrupole magnetic configuration
- 3. The inversion procedure
- 4. Application: Modelling of the magnetic field of Coronae Borealis
- 4.1. Observations
- 4.2. Analysis
- 4.3. Discussion
- 5. Conclusions
- Acknowledgements
- References
© European Southern Observatory (ESO) 2000
Online publication: June 20, 2000
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