Unresolved Binaries in the Intermediate Mass Range in the Pleiades Star Cluster

TL;DR

This study introduces a photometric method using pseudo-colors to estimate binary and multiple star ratios and their mass ratio distribution in the Pleiades cluster, focusing on intermediate-mass stars.

Contribution

The paper presents a novel photometric diagram approach to determine binary star ratios and mass ratio distributions in stellar populations.

Findings

Binary star ratio in Pleiades is between 0.54 and 0.70.

Multiple systems with more than two stars constitute about 10-14%.

Component mass ratio distribution follows a power law with exponent around -0.6.

Abstract

The identification of binary stars of different mass ratios in resolved stellar populations is a challenging task. We show how the photometric diagram constructed with the pseudo-colors (H-W2)-W1 vs W2-(BP-K) can be employed to estimate the binary and multiple star ratios and the distribution of their component mass ratio $q$ effectively. As an application, we investigate the Pleiades star cluster in the range of primary component mass between 0.5 and 1.8 $M_{\odot}$. The binary star ratio is found to be between 0.54$\pm$0.11 and 0.70$\pm$0.14. On the other hand, the ratio of systems with multiplicity more than 2 is between 0.10$\pm$0.00 and 0.14$\pm$0.01. The distribution of the component mass ratio $q$ has been approximated by a power law with the exponent between -0.53$\pm$0.10 and -0.63$\pm$0.22. Below 0.5 $M_{\odot}$, we expect a large number of brown dwarfs among secondary components.