Photographic photometry of star clusters in the small magellanic cloud

Photographic photometry of 20 star clusters and their adjoining fields has been carried out to determine the colour magnitude diagram for stellar systems in the Small Magellanic Cloud, using plates from the U.K. 1.2m Schmidt telescope. The W-N-E periphery of the Cloud has been examined.The main difficulty of the SMC star clusters is the contamination of cluster members by stars in the surrounding field.The evolutionary history of the star clusters seems to be similar to that of the surrounding field, implying that the background halo of the SMC is not well mixed.Old clusters have been found over the whole Cloud exhibiting differences in the morphology of the H-B which in most cases is very well populated at the red side of the RR Lyrae stars strip.Two more characteristics are i) the existence of very red stars (in three cases they are proved carbon stars) and ii) the large number of blue faint stars.The metallicity has been shown to be low in the SMC but the characteristics found in the old clusters are those normally found in intermediate age clusters of our Galaxy. Thus the age of the western halo clusters is ~10⁹ - 5 x 10⁹ yrs, whereas the northern halo clusters are even younger.The second group of clusters comprises young clusters which occupy the north part of the SMC or the north-east arm, since no young objects have been detected at the western part of this galaxy.The colour magnitude diagrams of the clusters and the adjoining field of the north-west arm give an age estimate of this feature of about 5 x 10⁷ yrs.The other small young clusters in the northern side of the Cloud are objects of the SMC disc and their ages are 10⁶ - 10⁷ years