EDP Sciences
Free access
Volume 390, Number 2, August I 2002
Page(s) 633 - 647
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20020726

A&A 390, 633-647 (2002)
DOI: 10.1051/0004-6361:20020726

Zeeman tomography of magnetic white dwarfs

I. Reconstruction of the field geometry from synthetic spectra
F. Euchner1, S. Jordan1, 2, 3, K. Beuermann1, B. T. Gänsicke1 and F. V. Hessman1

1  Universitäts-Sternwarte Göttingen, Geismarlandstr. 11, 37083 Göttingen, Germany
2  Institut für Astronomie und Astrophysik, Universität Kiel, 24098 Kiel, Germany
3  Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, 72076 Tübingen, Germany

(Received 7 February 2002 / Accepted 15 May 2002 )

We have computed optical Zeeman spectra of magnetic white dwarfs for field strengths between 10 and 200 MG and effective temperatures between 8000 and 40 000 K. They form a database containing 20 628 sets of flux and circular polarization spectra. A least-squares optimization code based on an evolutionary strategy can recover relatively complex magnetic field topologies from phase-resolved synthetic Zeeman spectra of rotating magnetic white dwarfs. We consider dipole and quadrupole components which are non-aligned and shifted off-centre. The model geometries include stars with a single high-field spot and with two spots separated by ~90°. The accuracy of the recovered field structure increases with the signal-to-noise ratio of the input spectra and is significantly improved if circular polarization spectra are included in addition to flux spectra. We discuss the strategies proposed so far to unravel the field geometries of magnetic white dwarfs.

Key words: white dwarfs -- stars: magnetic fields -- stars: atmospheres -- polarization

Offprint request: F. Euchner, feuchner@uni-sw.gwdg.de

© ESO 2002

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