Photometric binaries in Magellanic Cloud star clusters

Binary stars, with their potential to promote evolutionary scenarios at odds with standard single stellar models, have long been recognised as an interesting and important object in stellar astrophysics. Star clusters host a substantial amount of binaries, many of them being primordial. In the dense environment of Globular Clusters (GCs), one of the oldest objects in the universe, the elastic scatterings of binaries carry great significance. Binaries play a crucial role in energy distribution and in calculating cluster parameters such as age, radius, and mass function. Many of the exotic objects that have been frequently detected in the vast expanse of GCs, such as Blue straggler stars (BSSs) or cataclysmic variables, have evolutionary links with binaries in cluster environments. However, most of the studies on binaries are restricted to Galactic clusters which limit the accessible ranges of cluster parameters such as masses, ages, and densities. To broaden the cluster parameter range and better understand their impact on binary formation and evolution, we must look beyond the galaxy. Magellanic Cloud (MC) dwarf galaxies offer an extragalactic environment with its GCs spanning a wide range of ages and a mass range that is not spanned by both Galactic open and globular clusters. They do so while being close enough to study resolved stellar populations. The images collected with the Hubble Space Telescope are used to study fourteen star clusters of the MC dwarf galaxies that span an age interval between ∼ 0.6 and 2.1 Gyr and masses of 10,000 − 100,000 M⊙. Photometry is used to estimate the fraction of binary systems composed of two main-sequence (MS) stars, as well as the fraction of candidate BSSs. The distribution of binary fractions in terms of cluster and stellar parameters is also investigated. Moreover, the structural parameters of the cluster, including the core radius, central density, mass function, and total mass are also estimated. The fraction of binaries with a mass ratio larger than 0.7 was found to range from ∼7% to ∼20% depending on the cluster. The radial and luminosity distribution was observed to change from one cluster to another. The binaries are found to follow a flat distribution with the mass of the primary star and show no significant correlation with the mass ratio of the companion stars. Dynamically younger clusters formed a flat radial distribution while dynamically older clusters demonstrated evidence of segregation of binaries towards the center. The results on binaries in the studied MC clusters are combined with those obtained from homogeneous studies on 67 Galactic GCs and 78 open clusters (OCs). We detect a significant anti-correlation between the binary fraction in the core and the mass of the cluster. Conversely, there is no evidence of a correlation between the fraction of binaries and the cluster age or the dynamic age. The potential relation between binary fraction and the occurrence of other stellar populations, notably that of the BSSs, is an interesting topic. The fraction of BSSs is explored as a function of various cluster parameters and MS binary fractions. The radial distribution of BSSs is explored for their dynamical significance. The obtained results are compared with homogeneous studies on Galactic GCs and Ocs. Another population of stars was found to appear above the Red Clump (RC) region of the cluster. Their fraction is explored for their potential relation with different physical parameters of the cluster. To shed light on their formation scenarios, several binary interaction scenarios were investigated. A novel method was devised to detect low mass-ratio binaries which are considered inaccessible for binary fraction analysis due to photometric errors and their vicinity in the CMD to the MS stars.