******************************************************
   PR # 42190
   We propose to complete our program to measure the X-ray temperatures
   and iron abundances of the most distant, X-ray luminous clusters of
   galaxies known. The final cluster in our sample, MS1137+66 (z=0.78),
   is optically poorer than the other 3, and therefore probes a sparser
   galactic environment. We have observed clusters at z=0.55 and 0.83
   and find high Tx, consistent with Lx, but a low gas-to-total mass
   ratio (6%). The high redshift provides a long lever arm to test
   models for the evolution of the ICM and cluster formation. The
   cluster is bright and compact enough for ASCA spectra; the redshift
   moves the interesting part of the spectra to ~4 keV. It is chosen
   from a well-defined X-ray selected cluster sample. We have
   supplementary data from ROSAT, HST, CFHT and soon, Keck.
  ******************************************************