Magnetic field geometry and magnetospheric environment of the strongly magnetic Of?p star NGC 1624-2
| Autor: | Swetlana Hubrig, Markus Schöller, M. Küker, Ilya Ilyin, S D Chojnowski, Silva P. Järvinen |
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| Jazyk: | angličtina |
| Rok vydání: | 2021 |
| Předmět: |
Physics
Mathematics::Functional Analysis Field (physics) High Energy Physics::Lattice High Energy Physics::Phenomenology Doubly ionized oxygen Magnetosphere FOS: Physical sciences Astronomy and Astrophysics Geometry Magnetic field Nonlinear Sciences::Chaotic Dynamics Dipole Mathematics::Group Theory Mean field theory Astrophysics - Solar and Stellar Astrophysics Space and Planetary Science Polar Magnetohydrodynamics Solar and Stellar Astrophysics (astro-ph.SR) |
| Popis: | 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 $\langle B_z \rangle$ and the mean field modulus $\langle B \rangle$ to obtain constraints on its field geometry. Only one magnetic pole is observable over the rotation cycle. The approximately sinusoidal variation of $\langle B_z \rangle$ and the ratio of the values of the extrema of $\langle B \rangle$ indicate that there is an important component of the field that is dipolar. The $\langle B_z \rangle$ values measured over the rotation cycle are in the range from $-0.2$ to 4.5 kG, whereas the values for $\langle B \rangle$ vary between 9 and 12 kG. The $\langle B_z \rangle$ 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 $\langle B_z \rangle$ minimum coincides with the phase of the $\langle B \rangle$ 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. Comment: Accepted to be published in MNRAS |
| Databáze: | OpenAIRE |
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