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   PR #   138
   The 1.98 day eclipsing RS CVn-type binary AR Lac is one of the
   brighteststellar coronal sources. The eclipses offer the best
   opportunity to measurethe spatial structure of one of the most active
   X-ray emitting coronalplasma. We propose to observe AR Lac using ASCA
   for one complete binarycycle. EXOSAT observations have suggested the
   30 million degree emissioncomes from a region comparable in size to
   the binary separation,whereas the 7 million degree emission comes from
   more compact solar typeloops. ROSAT observations have contradicted
   this result. The better0.5-10 keV sensitivity of ASCA will resolve
   this discrepancy.
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