The search for mass segregation in star clusters of the Magellanic Clouds

The goal of this thesis is to determine the amount of mass segregation in star clusters as a function of their age-to-(relaxation time) ratios. We obtained B and V CCD images of five star clusters in the Magellanic Clouds using the four meter telescope at Cerro Tololo Inter-American Observatory. The clusters are: NGC 458, NGC 2249, NGC 2097, IC 2146, and 121SCO3. These clusters are rich in stars and span a broad range in age (approximately 300 million to 10 billion years). Stellar positions and magnitudes are determined using the DAOPHOT computer package. The ages, metallicities, distant moduli, and reddenings of the clusters are determined by fitting theoretical isochrones to their color-magnitude diagrams. Individual stars cannot be detected within one core radius of the center because of crowding. We derive numerical correction factors to the star count densities as a function of magnitude and radius. We then present a model for the completeness correction factors. Structural parameters are determined by fitting King models to the surface brightness profiles. Using these, we estimate the cluster masses and the two-body relaxation timescales and find that three clusters are unrelaxed (NGC 458, NGC 2097, and IC 2146) and two are relaxed (NGC 2249 and 121SCO3). We search for mass segregation by two different methods. The first is a pairwise comparison of the luminosity functions in different regions using K-S tests. We find significant differences in NGC 2249 and IC 2146, but not in the other clusters. The second method fits both multimass and single-mass King models to the joint combination of stellar number density profiles and surface brightness profiles. We are unsuccessful in detecting mass segregation because the data is fitted equally well by both types of models. The lack of significant differences in the second test is probably due to the inclusion of systematic uncertainties associated with the correction factors. We find a color gradient in the cores of NGC 2249 and 121SCO3 (both are centrally blue), which is consistent with these clusters being relaxed. <We suggest that future studies should be conducted with the use of the Hubble Space Telescope.