Discovery of magnetic fields in the $\beta$\,Cephei star
$\xi^1$\,CMa and in several Slowly Pulsating B stars

S. Hubrig$^1$, M. Briquet$^2$, M. Sch\"oller$^1$,
P. De Cat$^3$, G. Mathys$^1$, C. Aerts$^2$

$^1$ European Southern Observatory, Chile
$^2$ Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Belgium
$^3$ Koninklijke Sterrenwacht van Belgi\"e, Brussel, Belgium

We present the results of a magnetic survey of a sample of eight $\beta$\,Cephei
stars and 26 Slowly Pulsating B stars with FORS\,1 at the VLT. A weak
mean longitudinal magnetic field of the order of a few hundred Gauss is detected
in the $\beta$\,Cephei star $\xi^1$\,CMa and in 13 SPB stars. The star
$\xi^1$\,CMa becomes the third magnetic star among the $\beta$\,Cephei stars.
Before our study, the star $\zeta$\,Cas was the only known magnetic SPB star.
All magnetic SPB stars for which we gathered several magnetic field measurements
show a field that varies in time. We do not find a relation between the
evolution of the magnetic field with stellar age in our small sample. Our
observations imply that $\beta$\,Cephei stars and SPBs can no longer be
considered as classes of non-magnetic pulsators, but the effect of the fields
on the oscillation properties remains to be studied.

Reference: MNRAS
Status: Manuscript has been accepted