******************************************************                         
    PR # 32229                                                                   
     We propose to use the ASCA SIS to study the ubiquitous oxygen               
     absorption feature at unprecedented spectral resolution in Mrk 501.         
     We will also search for carbon K edge absorption, of which the SIS          
     should be capable of detecting if the ionization state is CIII or           
     higher.  This will enable us to distinguish ``warm'' (O IV + C IV) an       
     d ``hot'' (O VI + C VI) absorbing scenarios.  Mrk 501 is favorable, g       
     iven its low $N_H$, low $z$, and lack of cluster contamination, in  c       
     omparison to other BL Lacs studied with the SIS.  Indeed, a direct  c       
     omparison with Mrk 521 (which has simlilar variability properties)  s       
     hould be undertaken.  We will donate our data to help determine an  i       
     n-flight calibration for the SIS1 detector (which was apparently notc       
    alibrated below 1 keV on the g                                               
  ******************************************************