Article (Scientific journals)
X-ray emission from the giant magnetosphere of the magnetic O-type star NGC 1624-2
Petit, V.; Cohen, D. H.; Wade, G. A. et al.
2015In Monthly Notices of the Royal Astronomical Society, 453, p. 3288-3299
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Keywords :
stars: early-type; stars: individual: NGC 1624-2; stars: magnetic field; stars: massive; stars: winds; outflows; X-rays: stars
Abstract :
[en] We observed NGC 1624-2, the O-type star with the largest known magnetic field (B[SUB]p[/SUB] ˜ 20 kG), in X-rays with the Advanced CCD Imaging Spectrometer (ACIS-S) camera on-board the Chandra X-ray Observatory. Our two observations were obtained at the minimum and maximum of the periodic Hα emission cycle, corresponding to the rotational phases where the magnetic field is the closest to equator-on and pole-on, respectively. With these observations, we aim to characterize the star's magnetosphere via the X-ray emission produced by magnetically confined wind shocks. Our main findings are as follows. (i) The observed spectrum of NGC 1624-2 is hard, similar to the magnetic O-type star θ[SUP]1[/SUP] Ori C, with only a few photons detected below 0.8 keV. The emergent X-ray flux is 30 per cent lower at the Hα minimum phase. (ii) Our modelling indicated that this seemingly hard spectrum is in fact a consequence of relatively soft intrinsic emission, similar to other magnetic Of?p stars, combined with a large amount of local absorption (˜1-3× 10[SUP]22[/SUP] cm[SUP]-2[/SUP]). This combination is necessary to reproduce both the prominent Mg and Si spectral features, and the lack of flux at low energies. NGC 1624-2 is intrinsically luminous in X-rays (log L^{em}_X˜ 33.4) but 70-95 per cent of the X-ray emission produced by magnetically confined wind shocks is absorbed before it escapes the magnetosphere (log L^{ISMcor}_X˜ 32.5). (iii) The high X-ray luminosity, its variation with stellar rotation, and its large attenuation are all consistent with a large dynamical magnetosphere with magnetically confined wind shocks.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Petit, V.;  Department of Physics and Space Sciences, Florida Institute of Technology, Melbourne, FL 32904, USA
Cohen, D. H.;  Department of Physics and Astronomy, Swarthmore College, Swarthmore, PA 19081, USA
Wade, G. A.;  Department of Physics, Royal Military College of Canada, PO Box 17000, Stn Forces, Kingston, Ontario K7K 7B4, Canada
Nazé, Yaël  ;  Université de Liège - ULiège
Owocki, S. P.;  Department of Physics and Astronomy, University of Delaware, Bartol Research Institute, Newark, DE 19716, USA
Sundqvist, J. O.;  Department of Physics and Astronomy, University of Delaware, Bartol Research Institute, Newark, DE 19716, USA
ud-Doula, A.;  Penn State Worthington Scranton, Dunmore, PA 18512, USA
Fullerton, A.;  Space Telescope Science Institute, 3700 San Martin Dr, Baltimore, MD 21218, USA
Leutenegger, M.;  NASA/Goddard Space Flight Center, Code 662, Greenbelt, MD 20771, USA ; CRESST and University of Maryland, Baltimore County, Baltimore, MD 21250, USA
Gagné, M.;  Department of Geology and Astronomy, West Chester University, West Chester, PA 19383, USA)
Language :
English
Title :
X-ray emission from the giant magnetosphere of the magnetic O-type star NGC 1624-2
Publication date :
01 November 2015
Journal title :
Monthly Notices of the Royal Astronomical Society
ISSN :
0035-8711
eISSN :
1365-2966
Publisher :
Oxford University Press, Oxford, United Kingdom
Volume :
453
Pages :
3288-3299
Peer reviewed :
Peer Reviewed verified by ORBi
Available on ORBi :
since 01 October 2015

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