The strong magnetic field of the large-amplitude beta Cephei pulsator V1449 Aquilae
Résumé
Aims: Only for very few beta Cephei stars has the behaviour of the magnetic field been studied over the rotation cycle. During the past two years we have obtained multi-epoch polarimetric spectra of the beta Cephei star V1449 Aql with SOFIN at the Nordic Optical Telescope to search for a rotation period and to constrain the geometry of the magnetic field.
Methods: The mean longitudinal magnetic field is measured at 13 different epochs. The new measurements, together with the previous FORS 1 measurements, have been used for the frequency analysis and the characterization of the magnetic field.
Results: V1449 Aql so far possesses the strongest longitudinal magnetic field of up to 700 G among the beta Cephei stars. The resulting periodogram displays three dominant peaks with the highest peak at f = 0.0720 d-1 corresponding to a period P = 13ḍ893. The magnetic field geometry can likely be described by a centred dipole with a polar magnetic field strength Bd around 3 kG and an inclination angle beta of the magnetic axis to the rotation axis of 76 ± 4°. As of today, the strongest longitudinal magnetic fields are detected in the beta Cephei stars V1449 Aql and xi1 CMa with large radial velocity amplitudes. Their peak-to-peak amplitudes reach ~90 km s-1 and ~33 km s-1, respectively. Concluding, we briefly discuss the position of the currently known eight magnetic beta Cephei and candidate beta Cephei stars in the Hertzsprung-Russell (H-R) diagram.