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   PR # 22106
    The relatively unstudied, evolved SNR PKS 1209-52 (G296.5+10.0) has  
    an X-ray morphology and spectrum remarkably similar to the comparably
    -aged Cygnus Loop. However, unlike the Cygnus Loop, PKS 1209-52 has  
    virtually no optical filaments, and might contain a central stellar  
    remnant.  The lack of optical filaments might be due to PKS 1209-52  
    being at an earlier stage of interaction with the boundary of the    
    cavity in which it exploded.  We propose SIS observations of 3 loca- 
    tions along the X-ray bright rim, where the PSPC clearly reveals     
    temperature variations, to characterize conditions in the X-ray emit-
    ting gas:temperature, relative abundances (hence possibly the progen-
    itor mass), degree of departure from ionization equilibrium,         
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