The recently completed X-ray all-sky survey carried out by the ROSAT satellite can provide a sample of clusters of galaxies which has both well established quantifiable selection criteria and is in a contiguous region of the sky. To obtain this sample it is necessary to identify the clusters from the more numerous other sources. The Principal Investigator is only one of a few US astronomers who were invited to participate in the ROSAT survey and has access to this X-ray data well in advance of publication. This grant will provide support for follow-up optical studies of the cluster sample with particular emphasis on the initial identification of the clusters and later investigations of evolution of X-ray and optical properties, large scale structure, and the classical magnitude-redshift relation. Analysis of the ROSAT data will enable significant improvements over previous studies to be made.
