EDP Sciences
Free access
Volume 394, Number 3, November II 2002
Page(s) 1023 - 1037
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20021221

A&A 394, 1023-1037 (2002)
DOI: 10.1051/0004-6361:20021221

A statistical analysis of the magnetic structure of CP stars

S. Bagnulo1, M. Landi Degl'Innocenti2, M. Landolfi3 and G. Mathys1

1  European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile
    e-mail: sbagnulo@eso.org, gmathys@eso.org
2  C.N.R., Istituto di Radioastronomia, Sezione di Firenze, Largo E. Fermi 5, 50125 Firenze, Italy
    e-mail: mlandi@arcetri.astro.it
3  Istituto Nazionale di Astrofisica, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
    e-mail: landolfi@arcetri.astro.it

(Received 16 May 2002 / Accepted 6 August 2002 )

We present the results of a statistical study of the magnetic structure of upper main sequence chemically peculiar stars. We have modelled a sample of 34 stars, assuming that the magnetic morphology is described by the superposition of a dipole and a quadrupole field, arbitrarily oriented. In order to interpret the modelling results, we have introduced a novel set of angles that provides one with a convenient way to represent the mutual orientation of the quadrupolar component, the dipolar component, and the rotation axis. Some of our results are similar to what has already been found in previous studies, e.g., that the inclination of the dipole axis to the rotation axis is usually large for short-period stars and small for long-period ones - see Landstreet & Mathys (2000). We also found that for short-period stars (approximately $P<10\,\mathrm{days}$) the plane containing the two unit vectors that characterise the qua dru po le is almost coincident with the plane containing the stellar rotation axis and the dipole axis. Long-period stars seem to be preferentially characterised by a qua dru po le orientation such that the planes just mentioned are perpendicular. There is also some loose indication of a continuous transition between the two classes of stars with increasing rotational period.

Key words: stars: magnetic fields -- polarization -- stars: chemically peculiar

Offprint request: S. Bagnulo, sbagnulo@eso.org

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