Letter to the Editor

The strong magnetic field of the large-amplitude β Cephei pulsator V1449 Aquilae^⋆,⋆⋆

¹ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
e-mail: shubrig@aip.de
² Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200 D, 3001 Leuven, Belgium
³ LESIA, Observatoire de Paris, CNRS, UPMC, Université Paris-Diderot, 92195 Meudon, France
⁴ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
⁵ Instituto de Ciencias Astronomicas, de la Tierra, y del Espacio (ICATE), 5400 San Juan, Argentina
⁶ Koninklijke Sterrenwacht van België, Ringlaan 3, 1180 Brussel, Belgium
⁷ Institut d’Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août, Bât. B5c, 4000 Liège, Belgium

Received: 15 May 2011
Accepted: 17 June 2011

Abstract

Aims. Only for very few β 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 β 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 β 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 B_d around 3 kG and an inclination angle β of the magnetic axis to the rotation axis of 76 ± 4°. As of today, the strongest longitudinal magnetic fields are detected in the β Cephei stars V1449 Aql and ξ¹ 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 β Cephei and candidate β Cephei stars in the Hertzsprung-Russell (H-R) diagram.