EDP Sciences
Free access
Volume 423, Number 3, September I 2004
Page(s) 1081 - 1094
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:20040355

A&A 423, 1081-1094 (2004)
DOI: 10.1051/0004-6361:20040355

Discovery of kilogauss magnetic fields in three DA white dwarfs

R. Aznar Cuadrado1, S. Jordan2, 3, R. Napiwotzki4, H. M. Schmid5, S. K. Solanki1 and G. Mathys6

1  Max-Planck-Institut für Aeronomie, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany
    e-mail: aznar@linmpi.mpg.de
2  Institut für Astronomie und Astrophysik, Eberhard-Karls-Universität Tübingen, Sand 1, 72076 Tübingen, Germany
3  Astronomisches Rechen-Institut, Mönchhofstr. 12-14, 69120 Heidelberg, Germany
4  Department of Physics & Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
5  Institut für Astronomie, ETH Zentrum, 8092 Zürich, Switzerland
6  European Southern Observatory, Casilla 19001, Santiago 19, Chile

(Received 27 February 2004 / Accepted 12 May 2004)

We have detected longitudinal magnetic fields between 2 and 4 kG in three ( WD 0446-790 , WD 1105-048 , WD 2359-434 ) out of a sample of 12 normal DA white dwarfs by using optical spectropolarimetry done with the VLT Antu 8 m telescope equipped with FORS1. With the exception of 40 Eri B (4 kG) these are the first positive detections of magnetic fields in white dwarfs below 30 kG. Although suspected, it was not clear whether a significant fraction of white dwarfs contain magnetic fields at this level. These fields may be explained as relics from magnetic fields in the main-sequence progenitors considerably enhanced by magnetic flux conservation during the shrinkage of the core. A detection rate of 25% (3/12) may indicate now for the first time that a substantial fraction of white dwarfs have a weak magnetic field. This result, if confirmed by future observations, would form a cornerstone for our understanding of the evolution of stellar magnetic fields.

Key words: stars: magnetic fields -- stars: individual: WD0446-790 , WD1105-048 , WD2359-434

SIMBAD Objects

© ESO 2004