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Issue A&A
Volume 414, Number 1, January IV 2004
Page(s) L5 - L8
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20031723



A&A 414, L5-L8 (2004)
DOI: 10.1051/0004-6361:20031723

Letter

Coronal stripping in supersaturated stars

M. Jardine

School of Physics and Astronomy, North Haugh, St. Andrews KY16 9SS, Scotland, UK
(Received 2 September 2003 / Accepted 5 December 2003)

Abstract
A recent unambiguous detection of X-ray rotational modulation of the supersaturated star VXR45 ( P=0.223 days) has shown that its corona has discrete dark and bright X-ray regions. We suggest that due to the rapid rotation, the X-ray emitting corona has been centrifugally stripped away, creating open field regions that are dark in X-rays. This leads naturally both to a significant rotational modulation in X-rays but also to the lower X-ray luminosity of supersaturated stars compared to those rotating more slowly. To demonstrate the effect, we take as an example a more slowly rotating star for which surface magnetograms are available. We extrapolate the potential coronal magnetic field based on these magnetograms and determine for a hydrostatic, isothermal atmosphere the structure of the density and of the optically-thin X-ray emission. We show that if the rotation rate of this star were increased, the magnitude of the X-ray luminosity would decrease while its rotational modulation would increase in a way that is consistent with the recent observations of VXR45.


Key words: stars: activity -- stars: coronae -- stars: late-type -- stars: magnetic fields -- stars: rotation -- X-ray: stars

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© ESO 2004


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