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   51245
   The observation of very distant clusters(z>0.6) is a very powerful tool
   to constrain cosmological models, since different models predict very
   different number of massive clusters at high redshift. However the
   number of distant clusters for which spectroscopic X-ray measurements
   exist, and thus reliable mass estimate can be done, is still very
   small. We propose an very distant cluster, CL0107+31(z=0.69), for which
   we have detailed optical and infrared observations. This cluster have
   also or will be observed with ROSAT. Using the spectroscopic
   capabilities of ASCA, we will be able to measure the temperature and
   assess the total mass.
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