The structure and dynamics of young star clusters: King16, NGC1931, NGC637 and NGC189

In this paper, using 2MASS photometry, we study the structural and dynamical properties of four young star clusters viz. King16, NGC1931, NGC637 and NGC189. For the clusters King16, NGC1931, NGC637 and NGC189, we obtain the limiting radii of 7', 12', 6' and 5' which correspond to linear radii of 3.6pc, 8.85pc, 3.96pc and 2.8pc respectively. The reddening values E(B-V) obtained for the clusters are 0.85, 0.65-0.85, 0.6 and 0.53 and their true distances are 1786pc, 3062pc, 2270pc and 912pc respectively. Ages of the clusters are 6Myr, 4Myr, 4Myr and 10Myr respectively. We compare their structures, luminosity functions and mass functions ( phi (M)=dN/dM[/bo ld] M super(-(1+ chi ))) to the parameter tau =t sub( age )/t sub( relax ) to study the star formation process and the dynamical evolution of these clusters. We find that, for our sample, mass seggregation is observed in clusters or their cores only when the ages of the clusters are comparable to their relaxation times ( tau greater than or equal to 1). These results suggest mass seggregation due to dynamical effects. The values of chi , which characterize the overall mass functions for the clusters are 0.96 plus or minus 0.11, 1.16 plus or minus 0.18, 0.55 plus or minus 0.14 and 0.66 plus or minus 0.31 respectively. The change in chi as a function of radius is a good indicator of the dynamical state of clusters.