A&A 394, 1023-1037 (2002)

DOI: 10.1051/0004-6361:20021221

## A statistical analysis of the magnetic structure of CP stars

**S. Bagnulo**

^{1}, M. Landi Degl'Innocenti^{2}, M. Landolfi^{3}and G. Mathys^{1}^{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 )

** Abstract **

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
) 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

SIMBAD Objects

**©**

*ESO 2002*