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We present the initial results from our XMM program aimed at searching forX-ray activity cycles in solar-type stars. HD 81809 is a G2-type star (somewhatmore evolved than the Sun, and with a less massive companion) with a pronounced8.2 yr chromospheric cycle, as evident from from the Mt. Wilson program data.We present here the results from the initial 2.5 years of XMM observations,showing that large amplitude (a factor of approx. 10) modulation is present inthe X-ray luminosity, with a clearly defined maximum in mid 2002 and a steadydecrease since then. The maximum of the chromospheric cycle took place in 2001;if the observed X-ray variability is the initial part of an X-ray cycle, thiscould imply a phase shift between chromospheric and coronal activity, althoughthe current descent into chromospheric cycle minimum is well reflected into thestar's X-ray luminosity. The observations presented here provide clear evidencefor the presence of large amplitude X-ray variability coherent with theactivity cycle in the chromosphere in a star other than the Sun.Comment: Accepted for publication in A&

High-amplitude, long-term X-ray variability in the solar-type star HD 81809: The beginning of an X-ray activity cycle?