X-ray observations of the young open cluster Blanco 1

We present results from two deep ROSAT HRI exposures on the Blanco 1 open cluster. Blanco 1 is one of the few open clusters at large distance from the Galactic Plane. This circumstance has suggested that it may have formed through a mechanism different from that responsible for the other nearby clusters. The age of Blanco 1 is rather uncertain since, depending on the adopted age indicator, it ranges between 30 and 90 Myr. Many cluster members show chromospheric emission typical of young stars. The X-ray observations presented here reveal a high number of X-ray sources, consistent with the young age of the cluster. The typical X-ray luminosity of the cluster members is consistent with that of the Pleiades and significantly lower than the alpha Per members. These results suggest than the age of Blanco 1 is more similar to the age of the Pleiades than to that of alpha Per. The time sampling of the X-ray observations allows us to study the variability of the sources on time scales from hours to 6 months - 1 year.