Resolving Pleiades Binary Stars with Gaia and Speckle Interferometric Observations

Abstract

The Pleiades is the most prominent open star cluster visible from Earth and an important benchmark for simple stellar populations unified by common origin, age, and distance. Binary stars are its essential ingredient, yet their contribution remains uncertain due to heavy observational biases. A resolved multiplicity survey was conducted for a magnitude-limited G 4% are successfully resolved. We found that 10% of Pleiades stars have a companion with a mass ratio q > 0.5 within the projected separation of 27 300 au. An observed dearth of wide pairs with a large mass ratio ( q > 0.55) may imprint the transition from hard to soft binaries regime at the early stages of cluster evolution. The total binary fraction for q > 0.5 systems is extrapolated to be around 25%.

Keywords

• Open star clusters
• Speckle interferometry
• Visual binary stars