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   PR # 21519
    X-ray emission for hot gas has recently been observed in small       
    groups, like the well known case of the NGC2300 group (Mulchaey et al
    1993). Dynamical and photometric arguments however strongly suggest  
    that this should be considered a physical pair of galaxies rather    
    than a group. We propose to observe a set of physical galaxy pairs   
    morphologically and dynamically similar to NGC2300, to understand the
    role of mixed pairs in galaxy and group formation histories. We argue
    that mixed pairs are the nearly final stage of the coalescence of a  
    group. ASCA will therefore be crucial to measure the hot gas charac- 
    teristics, to determine the temperature and most important its       
    abundance, critical in distinguishing the primordial vs. interaction 
   origin of the intragalaxy gas.
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