A&A 406, L39-L42 (2003)
DOI: 10.1051/0004-6361:20030882

Letter

Evidence for coronal activity cycles on 61 Cygni A and B

A. Hempelmann¹, J. H. M. M. Schmitt¹, S. L. Baliunas² and R. A. Donahue<sup>2

1</sup>  Universität Hamburg, Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
    e-mail: ahempelmann@hs.uni-hamburg.de
²  Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 15, Cambridge, MA 02138, USA

(Received 2 May 2003 / Accepted 11 June 2003)

Abstract
We investigate a four-and-one-half year time-series of ROSAT HRI pointed observations of 61 Cyg A and B and compare the X-ray light curves with the chromospheric Ca HK variability. The ROSAT sampling rate was two pointings per year and typical errors lie in the range of 5-10%. The chromospheric cycles are well-known for both stars from the Mt. Wilson Ca HK survey. Although the time basis of our ROSAT observations is shorter than the 7-and 12-year cycles of components A and B, respectively, we find the long-term trend of coronal activity in close correlation with the chromospheric activity during the observation period, between 1993 and 1998. The chromospheric activity increased through maximum activity down to a minimum for component A, and from maximum to minimum activity for component B. The same behaviour is observed for the X-ray light curves but with much higher amplitudes by factors 2.5-3. The remaining scatter observed around low-order regression curves of coronal activity is small. We conclude that both stars do show coronal cycles and that coronal cycles are the dominant source of variability for 61 Cygni.

Key words: stars: late-type -- stars: activity -- stars: coronae -- stars: chromospheres

Offprint request: A. Hempelmann, ahempelmann@hs.uni-hamburg.de

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