A photometric survey of the Small Magellanic Cloud
The initial mass function (IMF) is defined as the fraction or number of stars born per unit mass interval and is the one of key parameters in astronomy. Since Salpeter (1955)'s work, there have been many studies, and most of them show the universality of the IMF regardless of systems, mass ranges, and metallicity within observational errors, although recently there are some suggestions of its variation. The main aim of this thesis is to test the IMF universality, based on a photometric study of the SMC. In order to study the IMF of massive stars and the star formation history, we perform a BVR photometric survey of the Small Magellanic Cloud (SMC), chosen for its proximity and low metallicity. The observational data were acquired at Siding Spring Observatory, Australia during the 5 - 11 September and 26 - 31 October 2001 and 9-17 November 2002, covering essentially the whole SMC area. Details of the instruments, characteristics of each run, and the procedures of data reduction are presented. We catalogued 0.76 million SMC stars brighter than 18 magnitude in B from total 1.3 millions. Regarding to the accuracy, we found 0.1 arcsecond in astrometry and 0.1 magnitude at B and V and 0.2 at R in photometry. Together with spectroscopic data, we investigate the basic parameters of the SMC such as colour excess, reddening and distance modulus, and compare them with other studies. Based on these parameters, we study the IMF and star formation histories using population synthesis techniques. In contrast to other authors, we transform the theoretical quantities into observable ones, and use Bayesian inference in the comparison of the various IMF models. The procedures and background concepts for the generation of models incorporating the same constraints as observed samples, are also described. According to model calculations, a continuous star formation model with an IMF slope of 1.6 offers the best representation of the SMC stars. Therefore we suggest that our result is one of the implications for the variation of the IMF, at least for hot stars.