## Abstract

We use high-resolution *Hubble Space Telescope* imaging observations of the young (∼ 15-25 Myr old) star cluster NGC 1818 in the Large Magellanic Cloud to derive an estimate for the binary fraction of F stars (1.3 < *M* _{*}/*M*_{⊙} < 1.6). This study provides the strongest constraints yet on the binary fraction in a young star cluster in a low-metallicity environment ([Fe/H] ∼ -0.4 dex). Employing artificial-star tests, we develop a simple method that can efficiently measure the probabilities of stellar blends and superpositions from the observed stellar catalog. We create synthetic color-magnitude diagrams matching the fundamental parameters of NGC 1818, with different binary fractions and mass-ratio distributions. We find that this method is sensitive to binaries with mass ratios *q* ≳ 0.4. For binaries with F-star primaries and mass ratios* q* > 0.4, the binary fraction is ∼0.35. This suggests a total binary fraction for F stars of 0.55 to unity, depending on assumptions about the form of the mass-ratio distribution at low *q*.

Original language | English |
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Pages (from-to) | 649-656 |

Number of pages | 8 |

Journal | Astrophysical Journal |

Volume | 724 |

Issue number | 1 |

DOIs | |

Publication status | Published - 20 Nov 2010 |

Externally published | Yes |

## Keywords

- binaries: general
- galaxies: star clusters: general
- Magellanic Clouds
- methods: statistical