Magnetic field geometry and magnetospheric environment of the strongly magnetic Of?p star NGC 1624-2

Abstract

NGC 1624-2 is an O7f?p star with a reported probable polar magnetic field strength $\ge$ 20 kG, which is the strongest magnetic field ever measured in an O-type star. We study the variability of the mean longitudinal magnetic field $⟨B_z⟩$ and the mean field modulus $⟨B⟩$ to obtain constraints on its field geometry. Only one magnetic pole is observable over the rotation cycle. The approximately sinusoidal variation of $⟨B_z⟩$ and the ratio of the values of the extrema of $⟨B⟩$ indicate that there is an important component of the field that is dipolar. The $⟨B_z⟩$ values measured over the rotation cycle are in the range from $-0.2$ to 4.5 kG, whereas the values for $⟨B⟩$ vary between 9 and 12 kG. The $⟨B_z⟩$ values obtained using the O III $\lambda$7455 emission line are in the range from 0.4 to 2.3 kG and show a variability pattern similar to that detected for the absorption lines. The fact that the phase of the $⟨B_z⟩$ minimum coincides with the phase of the $⟨B⟩$ maximum, indicates that the field structure must significantly depart from a centred dipole. Further, we discuss the nature of the observed variable Stokes $V$ profiles corresponding to a longitudinal field of negative polarity detected in the emission He I lines and present the first MHD numerical simulations of the gas flow in the magnetosphere of this star.

arXiv commentAccepted to be published in MNRAS

References in corpus (24)

• Mass-loss predictions for O and B stars as a function of metallicity
• Dynamical Simulations of Magnetically Channeled Line-Driven Stellar Winds: I. Isothermal, Nonrotating, Radially Driven Flow
• A Magnetic Confinement vs. Rotation Classification of Massive-Star Magnetospheres
• The MiMeS survey of magnetism in massive stars: Magnetic analysis of the O-type stars
• Magnetospheres and Disk Accretion in Herbig Ae/Be Stars
• PolarBase: a data base of high resolution spectropolarimetric stellar observations
• PEPSI: The high-resolution echelle spectrograph and polarimeter for the Large Binocular Telescope
• Discovery of a strong magnetic field on the O star HD 191612: new clues to the future of theta1 Orionis C?
• NGC 1624-2: A slowly rotating, X-ray luminous Of?cp star with an extraordinarily strong magnetic field
• Towards an understanding of the Of?p star HD 191612: optical spectroscopy
• Discovery of two magnetic massive stars in the Orion Nebula Cluster: a clue to the origin of neutron star magnetic fields?
• B fields in OB stars (BOB): Concluding the FORS2 observing campaign
• Discovery of a magnetic field in the O9 sub-giant star HD 57682 by the MiMeS Collaboration
• The spectral variability and magnetic field characteristics of the Of?p star HD 148937
• An `Analytic Dynamical Magnetosphere' formalism for X-ray and optical emission from slowly rotating magnetic massive stars
• VAMDC as a Resource for Atomic and Molecular Data and the New Release of VALD
• Confirming the oblique rotator model for the extremely slowly rotating O8f?p star HD 108
• X-ray emission from the giant magnetosphere of the magnetic O-type star NGC 1624-2
• Extreme resonance line profile variations in the ultraviolet spectra of NGC 1624-2: probing the giant magnetosphere of the most strongly magnetized known O-type star
• New observations of NGC 1624-2 reveal a complex magnetospheric structure and underlying surface magnetic geometry
• Two new chemically peculiar stars with resolved magnetically split lines
• The very slow rotation of the magnetic O9.7V star HD54879
• Mass loss and magnetospheres of massive stars
• The puzzling properties of the magnetic O star Tr16-22

Cited by in corpus (3)

• Are magnetic fields universal in O-type multiple systems?
• Detection of anomalous element distribution in the extremely slowly rotating magnetic O9.7 V star HD 54879
• Detection of extragalactic magnetic massive stars