Journal Article

A <i>ROSAT</i> observation of the eclipsing binary system XY UMa

R. D. Jeffries

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 295, issue 4, pages 825-833
Published in print April 1998 | ISSN: 0035-8711
Published online April 1998 | e-ISSN: 1365-2966 | DOI:
A ROSAT observation of the eclipsing binary system XY UMa

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The short-period, eclipsing, magnetically active binary system XY UMa has been observed over several orbital cycles at X-ray wavelengths. The X-ray light curves vary owing to obvious flares and other lower level activity on time-scales of days. These data caution against deducing coronal structure on the basis of a single orbit of X-ray data. In contrast to similar binary systems, XY UMa shows no significant X-ray eclipses. This is interpreted as evidence for either extended (> 1 R) coronae or a compact corona at high, uneclipsed latitudes on the primary star. The extended coronal scenario is favoured by some observational features of other systems such as extended radio coronae, long-duration X-ray flares and cool prominences, but unfavoured by others such as high coronal densities from EUV spectroscopy. A high-latitude compact corona might be associated with the high-latitude starspots seen in many active stars. Nearly simultaneous optical light curves suggest that some equatorial spots were present at the time of the X-ray observations, but fewer than in previous or subsequent years and that high-latitude spots must also be present. It is speculated that the lack of X-ray eclipses and dearth of equatorial, compact coronal regions are associated with a minimum in XY UMa's magnetic activity cycle.

Keywords: stars: activity; binaries: eclipsing; stars: coronae; stars: magnetic fields; stars: rotation; X-rays: stars

Journal Article.  0 words. 

Subjects: Astronomy and Astrophysics

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