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

A David-Uraz , C Erba , V Petit , A. W. Fullerton , Fabrice Martins (1) , N. R. Walborn , R. Macinnis , R. H. Barba , D. H. Cohen , J. Maiz Apellaniz , Y. Nazé , S. P. Owocki , J. O. Sundqvist , A. Ud-Doula , G. A. Wade

1 LUPM - Laboratoire Univers et Particules de Montpellier

In this paper, we present high-resolution HST/COS observations of the extreme magnetic O star NGC 1624-2. These represent the first ultraviolet spectra of this archetypal object. We examine the variability of its wind-sensitive resonance lines, comparing it to that of other known magnetic O stars. In particular, the observed variations in the profiles of the Civ and Siiv doublets between low state and high state are the largest observed in any magnetic O-type star, consistent with the expected properties of NGC 1624-2's magnetosphere. We also observe a redshifted absorption component in the low state, a feature not seen in most stars. We present preliminary modelling efforts based on the Analytic Dynamical Magnetosphere (ADM) formalism, demonstrating the necessity of using non-spherically symmetric models to determine wind/magnetospheric properties of magnetic O stars.

Domaines: Astrophysique stellaire et solaire [astro-ph.SR]

A David-Uraz, C Erba, V Petit, A. W. Fullerton, Fabrice Martins, et al.. 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. Monthly Notices of the Royal Astronomical Society, 2019, 483 (2), pp.2814-2824. ⟨10.1093/mnras/sty3227⟩. ⟨hal-01992841⟩