The strong magnetic field of the large-amplitude beta Cephei pulsator V1449 Aql

TL;DR

This study investigates the magnetic field behavior of the beta Cephei star V1449 Aql over its rotation cycle, revealing it has the strongest magnetic field among similar stars and characterizing its magnetic geometry.

Contribution

The paper provides the first detailed analysis of the magnetic field variation over the rotation cycle of V1449 Aql, including the magnetic geometry and period determination.

Findings

V1449 Aql has the strongest longitudinal magnetic field among beta Cephei stars (~700G).

The star's magnetic field likely has a centered dipole structure with a ~3kG polar strength.

The rotation period of V1449 Aql is approximately 13.9 days.

Abstract

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. The mean longitudinal magnetic field is measured at 13 different epochs. The new measurements, together with the previous FORS1 measurements, have been used for the frequency analysis and the characterization of the magnetic field. V1449 Aql so far possesses the strongest longitudinal magnetic field of up to 700G among the beta Cephei stars. The resulting periodogram displays three dominant peaks with the highest peak at f=0.0720d^-1 corresponding to a period P=13.893d. The magnetic field geometry can likely be described by a centred dipole with a polar magnetic field strength B_d around 3kG and an inclination angle beta of the magnetic axis to the rotation axis of 76+-4deg. As of today, the strongest longitudinal magnetic fields are detected in the beta Cephei stars V1449 Aql and xi^1 CMa with large radial velocity amplitudes. Their peak-to-peak amplitudes reach ~90km/s and ~33km/s, 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.