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Astron. Astrophys. 320, 831-839 (1997)

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ROSAT and AB Doradus: the first five years

M. Kürster 1, 2, J.H.M.M. Schmitt 1, G. Cutispoto 3 and K. Dennerl 1

1 Max-Planck-Institut für extraterrestrische Physik, Giessenbachstr., D-85740 Garching, Germany
2 Institut für Astronomie, Universität Wien, Türkenschanzstr. 17, A-1180 Wien, Austria (kurster@astro.ast.univie.ac.at)
3 Osservatorio Astrofisico, Viale A. Doria 6, I-95125 Catania, Italy

Received 21 May 1996 / Accepted 9 October 1996

Abstract

Five and a half years of data from an extensive ROSAT X-ray monitoring program devoted to the young K-star AB Dor are presented. Begun in mid-1990, this program is aimed at the study of the long-term behaviour of coronal flux levels in this very active star. We compare the X-ray data with 17 years of V-band brightness monitoring that shows a 10-year decline between 1978 and 1989 and a subsequent rise phase. In contrast, the X-ray flux, which is very variable on time scales of minutes to weeks, exhibits no pronounced long-term trend over the 5 1/2 years of the program. This supports the concept of a saturated corona. Making use of the ROSAT all-sky survey data and data from the most extensive among the available pointed observations we also discuss the short-term variablity in relation to the rotational time scale. We find evidence for a partial rotational modulation of the X-ray flux implying structural inhomogeneities in this saturated corona.

Key words: stars: coronae – stars: activity – stars: rotation – stars: individual: AB Dor – X-rays: stars

Send offprint requests to: M. Kürster

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998
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