Evolution and X-ray activity of the four Hyades giants

The nearby Hyades cluster harbors four giants, which have almost identicaloptical appearances. However, the activity of these very similar stars differs,with two stars being active, while the stars HD28305 and HD27697 are inactive\\:The Xray luminosities of these stars differ by more than a facor of 100! Anevolutionary study shows the former two at the beginning of their helium burningphase, while the latter two have already developed a carbon/oxygen core.Detailed Xray spectroscopy is available for the two bright giants, yet none forthe two fainter giants, for which we propose deep XMMNewton EPIC spectroscopy.We want to perform a detailed analysis of the Xray spectra, search for spectraldifferences and relate them to the different states of activity and stellar evolution. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]