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Description
We report the results of a complete X-ray survey of the Hyades cluster region using the ROSAT All-Sky Survey (RASS). Our survey covers over 900deg^2^ of the sky. Over 185 optically identified Hyades were detected down to a limiting X-ray luminosity of ~1-2x10^28^ergs/s (0.1-1.8keV); among solar-like stars, i.e., main-sequence stars of spectral type G, the RASS detection rate is ~90%. The presence of many binary systems in the cluster is a key factor influencing the X-ray luminosity function. Short-period (~ a few days or less) binaries are anomalously X-ray bright, as might be expected; however, the X-ray luminosity functions of K and possibly M binaries of all types are significantly different from their single counterparts, confirming the results of Pye et al. (1994MNRAS.266..798P) for a smaller K star sample drawn from deep ROSAT pointings. Comparison with Einstein Observatory studies of a subset of Hyades stars demonstrates a general lack of significant (> a factor of 2) long-term X-ray variability. This may be the result of the dominance of a small-scale, turbulent dynamo in the younger Hyades stars compared to the large-scale, cyclic dynamo observed in the Sun.
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