Coronal Activity and Variability in Stellar Clusters

Observations of X-ray emission from cool stars in nearby open cluster have proven to be crucial in our understanding of the prevalence, evolution, and variability of stellar coronae. More than two decades ago, the launch of the Einstein observatory and the subsequent discovery of X-ray emission from stars in the Hyades and Pleiades provided firm evidence for the coronal age-rotation-activity connection. Roughly a decade later, surveys of more than twenty open clusters with ROSAT greatly broadened our knowledge of these relationships. At the same time, these results raised important questions regarding coronal variability, ``saturation'', ``super-saturation'' in very rapid rotators, and differences in activity levels among clusters of similar age. In the EUV, open cluster studies have been much more limited. Yet this wavelength region is of prime importance to studies of both the solar corona (e.g. SOHO CDS/SUMER) and stellar coronae. In this context, I will discuss EUVE results for cluster stars, and address the potential for future observations. This work was supported in part by the Lockheed Martin Independent Research Program.