THE YOUNG LARGE MAGELLANIC CLOUD CLUSTERS NGC-2004 AND NGC-2100 AND THEIR SHORT-PERIOD VARIABLES

In this paper we present results of intensive CCD monitoring in the V-band of stars in two young LMC clusters: NGC2004 and 2100. Each star in these clusters was observed about 10- 1 5 times per night for about 1 2 nights, with the aim of detecting beta Cep stars in these metal-poor clusters and thereby testing the hypothesis that pulsation in these stars is driven by ionization of metals. Our results strongly support this idea, since we have failed to find any beta Cep variables. The probability that the difference between the relative numbers of beta Cep stars in the Galaxy and in these two clusters is due to chance is less than 0. 1 per cent. We have, however, found other types of short-period variable. We discuss the ages of these clusters and the strong differential reddening in NGC 2 1 00