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Article
A Multi-Phase Suzaku Study of τ Sco.
The Astrophysical Journal (2010)
  • Richard Ignace, East Tennessee State University
  • L. M. Oskinova, University Potsdam
  • M. Jardine, University of St Andrews
  • J. P. Cassinelli, University of Wisconsin
  • D. H. Cohen, Swarthmore College
  • J.-F. Donati, LATT, Observatoire Midi-Pyrenees
  • R. H. D. Townsend, University of Wisconsin
  • A. ud-Doula, Penn State Worthington Scranton
Abstract
We obtained relatively high signal-to-noise X-ray spectral data of the early massive star τ Sco (B0.2V) with the Suzaku X-ray Imaging Spectrometer (XIS) instrument. This source displays several unusual features that motivated our study: (1) redshifted absorption in UV P Cygni lines to approximately +250 km s−1 suggestive of infalling gas, (2) unusually hard X-ray emission requiring hot plasma at temperatures in excess of 10 MK whereas most massive stars show relatively soft X-rays at a few MK, and (3) a complex photospheric magnetic field of open and closed field lines. In an attempt to understand the hard component better, X-ray data were obtained at six roughly equally spaced phases within the same epoch of τ Sco’s 41 day rotation period. The XIS instrument has three operable detectors: XIS1 is back-illuminated with sensitivity down to 0.2 keV; XIS0 and XIS2 are front-illuminated with sensitivity only down to 0.4 keV and have an overall less effective area than XIS1. The XIS0 and XIS3 detectors show relatively little variability. In contrast, there is a ≈4σ detection of a ≈4% drop in the count rate of the XIS1 detector at one rotational phase. In addition, all three detectors show a ≈3% increase in count rate at the same phase. The most optimistic prediction of X-ray variability allows for a 40% change in the count rate, particularly near phases where we have pointings. Observed modulations in the X-ray light curve on the rotation cycle is an order of magnitude smaller than this, which places new stringent constraints on future modeling of this interesting magnetic massive star.
Keywords
  • Multi-Phase,
  • Suzaku,
  • τ Sco
Publication Date
October 1, 2010
DOI
10.1088/0004-637X/721/2/1412
Citation Information
Richard Ignace, L. M. Oskinova, M. Jardine, J. P. Cassinelli, et al.. "A Multi-Phase Suzaku Study of τ Sco." The Astrophysical Journal Vol. 721 (2010) ISSN: 0004-637X
Available at: http://works.bepress.com/richard_ignace/44/