The Spatial Distributions of Blue Main-sequence Stars in Magellanic Cloud Star Clusters

The color-magnitude diagrams of young star clusters show that, particularly at ultraviolet wavelengths, their upper main sequences (MSs) bifurcate into a sequence comprising the bulk population and a blue periphery. The spatial distribution of stars is crucial to understanding the reasons for these distinct stellar populations. This study uses high-resolution photometric data obtained with the Hubble Space Telescope to study the spatial distributions of the stellar populations in seven Magellanic Cloud star clusters. The cumulative radial number fractions of blue stars within four clusters are strongly anticorrelated with those of the high mass ratio binaries in the bifurcated region, with negative Pearson coefficients <-0.7. Those clusters are generally young or in an early dynamical evolutionary stage. In addition, a supporting N-body simulation suggests that the increasing percentage of blue MS stars from the cluster centers to their outskirts may be associated with the dissolution of soft binaries. This study provides a different perspective to explore the MS bimodalities in young clusters and adds extra puzzles. A more comprehensive study combined with detailed simulations is needed in the future.

Automated summary

The color-magnitude diagrams of young star clusters indicate a bifurcation of their upper main sequences at ultraviolet wavelengths. This study uses Hubble Space Telescope data to investigate the spatial distribution of stellar populations in seven Magellanic Cloud star clusters. The findings suggest a negative correlation between the radial number fractions of blue stars and high mass ratio binaries in certain clusters, which may be linked to the dissolution of soft binaries in young or early dynamical evolutionary stage clusters. Further comprehensive studies and simulations are needed to explore this phenomenon.