25 NRIAG Journal of Astronomy and Astrophysics, Special Issue, PP.339361, (2006) ____________________________________________________________________ *National Research Institute of Astronomy and Geophysics, Helwan, Cairo, Egypt. GALAXY PAIRS AND STAR FORMATION ACTIVITY IN HICKSON COMPACT GROUPS Ibrahim Selim*, Gamal. Bakr*, Hamed Ismail*, Ahmed Essam*, Ali Haroon* ABSTRACT: The effect of galaxy interaction on star formation in dense environment through the far-infrared emission (FIR) of galaxies has been investigated using data of Hickson Compact Groups (HCGs). We have identified 470 galaxy pairs with proximity criterion cr 6 390, and 358 galaxy pairs with (rp) less than 100 Kpc and V 6 350 km/s. We identified 41 close galaxy pairs with projected separations (rp) less than 25Kpc and difference in velocity V 6 100 km/s. The star formation rate (SFR) of galaxies in galaxy pairs is found to be enhanced for close galaxy pairs. The large fraction of star formation activity is probably due to the activity in the exchange of matter between the companions. The catalogue of galaxy pairs in HCGs has been established. INTRODUCTION From the theoretical point of view, interactions between galaxies have been investigated using both analytical and computer models. The first numerical simulations of galaxy interactions, built by Toomre (1976) show that many observed characteristics, such as morphological type, could be explained by these processes. Toomre and Toomre et al. (1972) argued that collisions of galaxies in groups and clusters could lead to galaxy merging with the formation of elliptical galaxies. This conclusion was confirmed later in numerical simulations by Schweizer (1989). Barnes (1990), who found that the observations and numerical simulations of galaxies gave evidence of effective interactions, collisions and merging which continued to reshape and feed galaxies up to the present days. Barnes et al (1996) and Mihos et al (1996) concluded that the interactions between systems may induce gas inflows to the central region of the systems, triggering starburst. Different observations have shown that galaxy interactions and merging are powerful mechanisms to trigger star formation in galaxies (e.g. Larson et al. 1987; Donzelli et al 1997; Ellingson 1995; Pastoriza 1997 and Kennicutt et al 1998). The interactions during close encounters could be correlated with enha