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A multiphase Suzaku study of X-rays from τ Sco

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Date
01/10/2010
Author
Ignace, R.
Oskinova, L. M.
Jardine, M.
Cassinelli, J. P.
Cohen, D. H.
Donati, J.-F.
Townsend, R. H. D.
ud-Doula, A.
Funder
Science & Technology Facilities Council
Grant ID
ST G001987 1
Keywords
Stars: early-type
Stars: individual: τ Sco
Stars: magnetic field
Stars: winds
Outflows
X-rays: stars
QB Astronomy
QC Physics
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Abstract
We obtained relatively high signal-to-noise X-ray spectral data of the early massive star tau 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 tau 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 approximate to ≈4 sigma detection of a approximate to ≈4% drop in the count rate of the XIS1 detector at one rotational phase. In addition, all three detectors show a approximate to ≈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.
Citation
Ignace , R , Oskinova , L M , Jardine , M , Cassinelli , J P , Cohen , D H , Donati , J-F , Townsend , R H D & ud-Doula , A 2010 , ' A multiphase Suzaku study of X-rays from τ Sco ' , Astrophysical Journal , vol. 721 , no. 2 , pp. 1412-1420 . https://doi.org/10.1088/0004-637X/721/2/1412
Publication
Astrophysical Journal
Status
Peer reviewed
DOI
https://doi.org/10.1088/0004-637X/721/2/1412
ISSN
0004-637X
Type
Journal article
Rights
© 2010, American Astronomical Society. This work has been made available online in accordance with the publisher’s policies. This is the final published version of the work, which was originally published at iopscience.iop.org / http://dx.doi.org/10.1088/0004-637X/721/2/1412
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  • University of St Andrews Research
URL
http://adsabs.harvard.edu/abs/2010ApJ...721.1412I
URI
http://hdl.handle.net/10023/9829

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