Resolving Pleiades binary stars with Gaia and speckle interferometric observations

TL;DR

This study combines Gaia data and speckle interferometry to resolve and analyze binary star systems in the Pleiades cluster, revealing new binaries, confirming known companions, and providing insights into binary fractions and distributions.

Contribution

It introduces a combined observational approach to identify and characterize binary stars in the Pleiades, including new discoveries and analysis of binary properties.

Findings

Identified 61 binary/multiple systems within 0.04-10 arcsec separation.

Discovered 21 new components in 20 systems.

Estimated a total binary fraction of around 25% for q > 0.5 systems.

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 < 15mag sample of 423 potential cluster members, including sources with poorly fitted astrometric solutions in Gaia DR3. Speckle interferometric observations at the 2.5 meter telescope of SAI MSU observatory were combined with Gaia data, enabling the identification of 61 resolved binary or multiple systems within the 0.04 - 10 arcsec (5 - 1350 au) separation range. With speckle observations, we discovered 21 components in 20 systems. The existence of a Merope (23 Tau) companion is confirmed after several previous unsuccessful attempts. We show that the Gaia multipeak fraction is a strong predictor of subarcsecond multiplicity, as all sources with ipd_frac_multi_peak > 4% are successfully resolved. We found that 10% of Pleiades stars have a companion with a mass ratio q > 0.5 within projected separation of 27 < s < 1350 au, and confirm a deficit of wide binaries with s > 300 au. An observed dearth of wide pairs with 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%.