Photometric binaries in 14 Magellanic Cloud star clusters

¹ Dipartimento di Fisica e Astronomia “Galileo Galilei”, Università Degli Studi di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
e-mail: anjana.mohandasan@studenti.unipd.it
² Istituto Nazionale di Astrofisica – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
³ Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia
⁴ South-Western Institute for Astronomy Research, Yunnan University, Kunming 650500, PR China
⁵ Center for Galaxy Evolution Research and Department of Astronomy, Yonsei University, Seoul 03722, Korea
⁶ Istituto Nazionale di Astrofisica – Osservatorio Astronomico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy
⁷ Department of Physics and Astronomy, Uppsala University, Box 516 751 20 Uppsala, Sweden

Received: 10 July 2023
Accepted: 17 October 2023

Abstract

Binary stars play a major role in determining the dynamic evolution of star clusters. We used images collected with the Hubble Space Telescope to study fourteen star clusters of the Magellanic Clouds that span an age interval between ∼0.6 and 2.1 Gyr and masses of 10⁴ − 10⁵ M_⊙. We estimated the fraction of binary systems composed of two main-sequence stars and the fraction of candidate blue-straggler stars (BSSs). Moreover, we derived the structural parameters of the cluster, including the core radius, central density, mass function, and total mass. We find that the fraction of binaries with a mass ratio larger than 0.7 ranges from ∼7% in NGC 1846 to ∼20% in NGC 2108. The radial and luminosity distribution can change from one cluster to another. However, when we combine the results from all the clusters, we find that binaries follow a flat radial trend and no significant correlation with the mass of the primary star. We find no evidence for a relation between the fractions of binaries and BSSs. We combined the results on binaries in the studied Magellanic Cloud clusters with those obtained for 67 Galactic globular clusters and 78 open clusters. We detect a significant anti-correlation between the binary fraction in the core and the mass of the host cluster. However, star clusters with similar masses exhibit a wide range of binary fractions. Conversely, there is no evidence of a correlation between the fraction of binaries and the cluster age or the dynamic age.