New insights into the formation of the blue main sequence in NGC 1850

TL;DR

This study investigates the origin of the blue main sequence in NGC 1850, suggesting it may consist of low-mass-ratio binary stars rather than solely rapidly rotating stars, based on spatial distribution analysis.

Contribution

It provides observational evidence linking blue main sequence stars to low-mass-ratio binaries, offering a new perspective on their formation in young clusters.

Findings

Blue-MS stars are likely low-mass-ratio binaries.

High-mass-ratio binaries are more centrally concentrated.

Blue-MS stars show a strong anti-correlation with high-mass-ratio binaries.

Abstract

Recent discoveries of bimodal main sequences (MSs) associated with young clusters (with ages $\lesssim 1$ Gyr) in the Magellanic Clouds have drawn a lot of attention. One of the prevailing formation scenarios attributes these split MSs to a bimodal distribution in stellar rotation rates, with most stars belonging to a rapidly rotating population. In this scenario, only a small fraction of stars populating a secondary blue sequence are slowly or non-rotating stars. Here, we focus on the blue MS in the young cluster NGC 1850. We compare the cumulative number fraction of the observed blue-MS stars to that of the high-mass-ratio binary systems at different radii. The cumulative distributions of both populations exhibit a clear anti-correlation, characterized by a highly significant Pearson coefficient of $-0.97$. Our observations are consistent with the possibility that blue-MS stars are low-mass-ratio binaries, and therefore their dynamical disruption is still ongoing. High-mass-ratio binaries, on the other hand, are more centrally concentrated.