Blue straggler stars beyond the Milky Way. II. A binary origin for blue straggler stars in Magellanic Cloud clusters

TL;DR

This study investigates blue straggler stars in Magellanic Cloud clusters, finding that binary interactions are likely the main formation mechanism, with stellar collisions playing a minor role.

Contribution

It provides the first comprehensive analysis of BSS populations in Magellanic Cloud clusters, highlighting the dominance of binary interactions in BSS formation.

Findings

BSS numbers correlate sub-linearly with cluster core mass

Binary interactions likely dominate BSS formation

Stellar collisions contribute less than 20% to BSS population

Abstract

We have analyzed populations of blue straggler stars (BSSs) in 24 Magellanic Cloud star clusters using multi-passband Hubble Space Telescope images. We compiled a homogeneous BSS database, containing both traditional and evolved BSSs. We uncovered a sub-linear correlation between the number of BSSs in the cluster cores and the clusters' core masses, characterized by a power-law index of $0.51\pm 0.07$. For low stellar collision rates, the mass-normalized number of BSSs depends only weakly (or perhaps not at all) on the collision rate, implying that the binary-driven BSS formation channel dominates. Comparison with simulations suggests that stellar collisions contribute less than 20\% to the total number of BSSs formed. Further tests, including analysis of the BSS specific frequencies and their population numbers at larger cluster radii, suggest that binary interactions may be their main formation channel, hinting at an anti-correlation between a cluster's binary fraction and its core mass.