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 (1), C. Erba (1), V. Petit (1), A. W. Fullerton (2), F. Martins (3), N. R. Walborn (2), R. MacInnis (1), R. H. Barbá (4), D. H. Cohen (5), J. Maíz Apellániz (6), Y. Nazé (7), S. P. Owocki (1), J. O. Sundqvist (8), A. ud-Doula (9), G. A. Wade (10)

(1) Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA, (2) Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA, (3) LUPM-UMR 5299, CNRS & Universit\'e Montpellier, Place Eugene Bataillon, 34095 Montpellier Cedex 05, France, (4) Departamento de F\'isica y Astronom\'ia, Universidad de La Serena, Av. Cisternas 1200 Norte, La Serena, Chile, (5) Department of Physics and Astronomy, Swarthmore College, Swarthmore, PA 19081, USA, (6) Centro de Astrobiolog\'ia, CSIC-INTA. Campus ESAC. Camino bajo del castillo s/n. E-28 692 Villanueva de la Ca\~nada. Spain, (7) Universit\'e de Li\`ege, Quartier Agora (B5c, Institut d'Astrophysique et de G\'eophysique), All\'ee du 6 Ao\^ut 19c, B-4000 Sart Tilman, Li\`ege, Belgium, (8) Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium, (9) Penn State Scranton, 120 Ridge View Drive, Dunmore, PA 18512, USA, (10) Department of Physics and Space Science, Royal Military College of Canada, PO Box 17000, Stn Forces, Kingston, Ontario K7K 7B4, Canada

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.

Reference: arXiv:1811.10113
Status: Manuscript has been accepted

Weblink: https://arxiv.org/abs/1811.10113

Comments: 13 pages, 6 figures, accepted for publication by MNRAS

Email: adu@udel.edu