Journal Article

The contribution of star-spots to coronal structure

D. Arzoumanian, M. Jardine, J.-F. Donati, J. Morin and C. Johnstone

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 410, issue 4, pages 2472-2480
Published in print February 2011 | ISSN: 0035-8711
Published online January 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.17623.x
The contribution of star-spots to coronal structure

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Significant progress has been made recently in our understanding of the structure of stellar magnetic fields, thanks to advances in detection methods such as Zeeman–Doppler Imaging. The extrapolation of this surface magnetic field into the corona has provided three-dimensional models of the coronal magnetic field and plasma. This method is sensitive mainly to the magnetic field in the bright regions of the stellar surface. The dark (spotted) regions are censored because the Zeeman signature there is suppressed. By modelling the magnetic field that might have been contained in these spots, we have studied the effect that this loss of information might have on our understanding of the coronal structure. As examples, we have chosen two stars (V374 peg and AB Dor) that have very different magnetograms and patterns of spot coverage. We find that the effect of the spot field depends not only on the relative amount of flux in the spots, but also on its distribution across the stellar surface. For a star such as AB Dor with a high spot coverage and a large polar spot, at its greatest effect the spot field may almost double the fraction of the flux that is open (hence decreasing the spin-down time) while at the same time increasing the X-ray emission measure by 2 orders of magnitude and significantly affecting the X-ray rotational modulation.

Keywords: techniques: polarimetric; stars: coronae; stars: imaging; stars: individual: V374 Peg; stars: individual: AB Dor; starspots

Journal Article.  6865 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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