MASS SEGREGATION IN YOUNG LARGE-MAGELLANIC-CLOUD CLUSTERS - I - NGC-2157

We have carried out Wide Field Planetary Camera 2 V-and I-band imaging of the young LMC cluster NGC 2157. Construction of a color-magnitude diagram and isochrone fitting yield an age of tau = 10(8) yr, a redden ing E(B-V) = 0.1, and a distance modulus of 18.4 mag. Our data cover t he mass range 0.75 M. less than or equal to m less than or equal to 5. 1 M.. We find that the cluster mass function changes significantly fro m the inner regions to the outer regions, becoming steeper (larger num ber of low-mass stars relative to high-mass stars) at larger radii. Th e age of NGC 2157 is comparable to its two-body relaxation timescale o nly in the cluster core. The observed steepening of the mass function at larger radii is therefore most likely an initial condition of the c luster stars, Such initial conditions are predicted in models of clust er star formation in which dissipative processes act more strongly upo n more massive stars.