TESTING THE PHYSICAL REALITY OF BINARIES AND COMPACT-GROUPS - PROPERTIES OF EARLY-TYPE GALAXIES IN GROUPS WITH DIFFUSE-X-RAY EMISSION

We present data on the stellar kinematics of the brightest ellipticals in HCG 62, HCG 68, NGC 2300 groups. Moreover, we report on ASCA GIS a s well as optical observations of the early-type member of the pair K 416 (NGC 5480/5481) similar, in many respects, to the dominant pair in the NGC 2300 group. The kinematics of HCG 62a/b and HCG 68a/b indicat e that they are not interacting pairs. HCG 62a is instead possibly int eracting with HCG 62c, as suggested by their morphology (see Mendes de Oliveira and Hickson 1994). In contrast to the results for the NGC 23 00/2276 group, ASCA observations indicate a significant absence of hot gas in the K 416 system. Whether the NGC 2300 multiplet is viewed as a loose group or as a massive E+S pair, it is clear that similar morph ological entities do not always show similar X-ray properties. Under t he hypothesis that diffuse X-ray emission marks the group potential, w e consider the possibility that K 416 is an unbound encounter. In this scenario, morphological distortions are indicative of the ongoing int eraction, but are only circumstantially correlated with the physical r eality of a pair/multiplet as a bound system.